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Earth

Earth

Imagine that you are describing planet Earth to someone who has never seen it. How would you describe its appearance? What would you say about it? What things about Earth are typical of all planets? What things are unique?

To describe Earth, you might say that it is the third planet from the Sun in this solar system, and that it is 12,756 kilometers (7,909 miles) in diameter. Someone else might say that Earth is a fragile-looking blue, brown, and white sphere. A third person might say that Earth is the only planet in our system, as far as we know, with life. All of these descriptions are true; they are very different, however, from the descriptions of Earth that someone living in the 1950s or earlier would have given. Before we began to travel into space and to send spacecraft to observe other planets, we did not realize how different, or how similar, our planet was from other planets. And we were so busy examining the details and small regional differences of our world that we did not think about the planet as a whole.

Planet Earth

Our knowledge of Earth has been fundamentally changed by the knowledge we have gained about the other planets in the solar system. We have come to realize that, in some ways, Earth is very similar to its nearest neighbors in space. Like all of the other planets in our system, Earth orbits around our star (the Sun). It is the largest of the inner planets, just slightly larger than Venus; and it experiences seasons (as does Mars) due to the tilt of its rotation axis.

Like many other planets in our system, Earth has a natural satellite. We call our single satellite the "Moon" and have used that term to describe all of the other moons in our system, although Earth and its Moon are unusually closer in size than is common. One of the ways in which Earth is similar to its nearest neighbors is that all of the "rocky" planets have been affected by four fundamental geological processes: volcanism, tectonism , erosion, and impact cratering.

The surface of our planet is a battleground between the processes of volcanism and tectonism that create landforms and the process of erosion that attempts to wear away these landforms. Geologically speaking, Earth is a "water-damaged" planet, because water is the dominant agent of erosion on the surface of our world. On planets with little or no atmosphere, erosion of the surface may occur due to other processes, such as impact cratering. On the rocky planets the dominant mechanism of erosion may differ, and the styles or details of the volcanic or tectonic landscape may differ, but the fundamental geological processes remain the same.

Of the four fundamental processes, the one that may be unexpected is impact cratering. In fact, prior to our exploration of the Moon, impact cratering was not considered important to Earth. Those few impact craters identified on Earth were treated as curiosities. Now, after studying the other planets, we realize that impact cratering is an important and continuing process on all planets, including Earth. Impacts from meteorites , comets, and occasionally large asteroids have occurred throughout the history of Earth and have been erased by Earth's dynamic and continuing geology. The formation of an impact crater can significantly affect the geology, atmosphere, and even the biology of our world. For example, scientists believe that an impact that occurred about 65 million years ago on the margin of the Yucatan Peninsula was a possible cause of the extinction of the dinosaurs and many other species.

A Uniquely Different Planet

Although Earth is in some ways a typical rocky planet, several of its most interesting features appear to be unique. For example, a global map of Earth with the ocean water removed shows a very different planet from our neighboring rocky planets. The patterns made by continents, oceans, aligned volcanoes, and linear mountains are the result of the process geologists call plate tectonics.

We know from the study of earthquake waves moving through Earth that our planet is made up of three main layers: the crust, mantle, and core. The upper layer of Earth (consisting of the crust and the upper mantle) is broken into rigid plates that move and interact in various ways. Where plates are moving together or one plate is moving beneath another, mountains such as the Himalayas or explosive volcanoes such as the Cascades are formed. Where plates are moving apart, such as along the mid-oceanic ridges, new crust is formed by the slow eruption of lava. Where two plates slide along each other, such as the San Andreas Fault zone in California, major earthquakes occur. The movement of the plates is caused by the convection of the mantle beneath them; that convection is driven by the planet's internal heat, derived from radioactive decay of certain elements. Similarly, rotation and convection in the fluid metallic outer core is responsible for Earth's uniquely strong magnetic field. Plate tectonics can be thought of as a giant recycling mechanism for Earth's crust.

The concept of plate tectonics is a relatively new idea, and it is central to our understanding of Earth's dynamic geology. Nevertheless, planetary geologists have found no clear evidence of past or present Earth-style plate tectonics on any of the other rocky planets; Earth seems to be unique in this regard.

Earth is also unique in that no other planet in the solar system currently has the proper temperature and atmospheric pressure to maintain liquid water on its surface. Water exists on Earth as gas (water vapor), liquid, and solid (ice), and all three forms are stable at Earth's surface temperature and pressure. Water may be the single most important criteria for life as it has developed on Earth. And the presence of life, in turn, has changed and affected the composition of the atmosphere and the surface of Earth. For example, the rock type limestone would not be possible without marine life, and limestone formation may have significantly altered the distribution of carbon dioxide on Earth.

Mars and Venus also have atmospheres, but they are primarily composed of carbon dioxide. Earth's atmosphere is approximately 76 percent nitrogen and 20 percent oxygen with traces of water vapor, carbon dioxide, and ozone. Although water is not a major component by percent, it is a very important part of Earth's atmosphere. Earth's surface water and atmosphere are linked to form a single system. Water evaporates from the oceans, moves through the atmosphere as vapor or cloud droplets, precipitates onto the surface as rain or snow, and returns to the oceans by way of rivers. Clouds cover approximately 50 percent of Earth's surface at any one time, and they play an important role in maintaining the balance of atmospheric and surface temperatures on our planet.

Our atmosphere and water work together to form a general category of rocks on Earth that is not known to exist on any neighboring planets. On Earth's surface, sedimentary rocks, such as quartz-rich sandstone or marine limestone, are very common; they cover approximately 70 percent of the surface of our planet in a very thin veneer. Although Mars may surprise us, initial studies of our nearest neighbors indicate that the volcanic rock basalt is the basic building block of planetary crust (including most of Earth's subsurface crust) and the most common rock type on the surface of the other rocky planets. Once again, Earth is unique. And as we explore other planets around other suns, typical Earth sandstone might be as exotic and rare as gold.

see also Close Encounters (volume 2); Earthwhy Leave? (volume 4); Mars (volume 2); Moon (volume 2); NASA (volume 3); Solar Wind (volume 2).

Jayne Aubele

Bibliography

Cloud, Preston. Oasis in Space: Earth History from the Beginning. New York: W. W.Norton and Company, 1988.

Hamblin, W. Kenneth, and Eric H. Christiansen. Exploring the Planets. New York:Macmillan Publishing Company, 1990.

Harris, Stephen L. Agents of Chaos. Missoula, MT: Mountain Press Publishing Company, 1990.

Moore, Patrick, and Garry Hunt, eds. Atlas of the Solar System. New York: Crescent Books, 1990.

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Earth

Earth

Earth, the third planet from the Sun, is our home planet. Its surface is mostly water (about 70 percent) and it has a moderately dense nitrogen-and-oxygen atmosphere that supports lifethe only known life in the universe. From space, Earth appears as a shining blue ball with white swirling clouds covering vast oceans and irregular-shaped landmasses that are varying shades of green, yellow, brown, and white.

Earth orbits the Sun at a distance of about 93,000,000 miles (150,000,000 kilometers), taking 365.25 days to complete one elliptical (oval-shaped) revolution. The planet rotates once about its axis almost every 24 hours. It is not truly spherical, but bulges slightly at its equator. Earth's diameter at the equator is roughly 7,926 miles (12,760 kilometers), while its diameter at the poles is 7,900 miles (12,720 kilometers). The circumference of Earth at its equator is about 24,830 miles (40,000 kilometers).

Earth's only natural satellite, the Moon, orbits the planet at an average distance of about 240,000 miles (385,000 kilometers). Some scientists believe that Earth and the Moon should properly be considered a double planet, since the Moon is larger relative to our planet than the moons of most other planets.

Unlike the outer planets, which are composed mainly of light gases, Earth is made of heavy elements such as iron and nickel, and is therefore much denser. Hot at first due to the collisions that formed it about 4.5 million years ago, Earth began to cool. Its components began to separate themselves according to their density. Heavy abundant elements, iron and nickel, formed Earth's core. Outside the core numerous elements were compressed into a dense but pliable (bendable) substance called the mantle. Finally, a thin shell of cool, silicon-rich rock formed at Earth's surface, called the crust or lithosphere. Formation of the crust from the initial molten blob took half a billion years.

Earth's atmosphere

Earth's atmosphere is the only planetary atmosphere in the solar system capable of sustaining life. It is made of 78 percent nitrogen, 21 percent oxygen, and a 1 percent mixture of gases dominated by argon.

Various theories have been proposed as to the origin of these gases. One theory states that when Earth was formed, the gases were trapped in layers of rock beneath the surface. They eventually escaped, primarily through volcanic eruptions, to form the atmosphere. Water vapor was the most plentiful substance spewed out, and condensed (change from a gas to a liquid) to form the oceans. Carbon dioxide was second in terms of quantity, but most of it dissolved in the ocean waters or was altered chemically through reactions with other substances in the rocks. Nitrogen came out in smaller amounts, but always remained in its present form because it never underwent reactions or condensation. It is believed that for that reason, nitrogen is the most abundant gas in the atmosphere today.

Oxygen only became a part of Earth's atmosphere when green plants came into being. Through the process called photosynthesis, green plants convert carbon dioxide into oxygen. Oxygen is also removed from the atmosphere when green plants, as well as animals, die. As they decay, they oxidize, a process that uses up oxygen.

Another more recent theory regarding the development of Earth's atmosphere states that the elements found in it were deposited there by comets. Debris from comets has been shown to have carbon and nitrogen in roughly the same proportion as the atmosphere. During its early development, Earth was the site of repeated comet collisions.

Ninety-nine percent of the atmosphere's mass is contained in the first 40 to 50 miles (65 to 80 kilometers) above Earth's surface. This relatively thin atmosphere insulates the planet by allowing the Sun's visible light to pass through the atmosphere and warm the surface. The resulting

heat (infrared radiation) is reradiated from the surface, but is prevented from totally escaping back into space by carbon dioxide, methane, and water vapor in the atmosphere. These so-called greenhouse gases absorb most of this energy and re-emit back to the surface, keeping the planet at relatively stable, warm temperatures. The average surface temperature is 59°F (15°C).

While keeping in necessary heat radiation, components in the atmosphere block dangerous forms of radiation from reaching the surface. These include X rays and ultraviolet radiation, which is absorbed by the ozone layer located at about 15 miles (24 kilometers) above Earth's surface.

Earth's surface

The surface of Earth is divided into dry landmasses and oceans. Landmasses occupy roughly 57.5 million square miles (148.9 million square kilometers) of the planet's surface, while oceans cover roughly 139.5 million square miles (361.3 square kilometers).

Landmasses are in a constant, though slow, state of change. They move, collide, and break apart according to a process called plate tectonics. The lithosphere is not one huge shell of rock; it is composed of several large pieces called plates. These pieces are constantly in motion, because Earth's interior is dynamic, with its core still molten (liquid) and with large-scale convective (circulating) currents in the upper mantle. This resulting giant furnace beneath the surface moves land no more than a few centimeters a year, but this is enough to have profound consequences. The unending cycle of mountain building (caused by movement of the crustal plates) and erosion (by wind and water) has formed every part of Earth's surface today.

Earth is mostly covered with water. The mighty Pacific Ocean covers nearly half of the globe. The existence of oceans implies that there are large areas of the lithosphere that are lower than others, which form huge basins. Early in the planet's history these basins filled with water condensing (raining) out of the primordial (primitive) atmosphere. Additional water was brought to Earth by impacting comets, whose nuclei were made of water and ice.

The atmosphere has large circulation patterns, and so do the oceans. Massive streams of warm and cold water flow through them. Circulation patterns in the oceans and in the atmosphere are driven by temperature differences between adjacent areas and by the rotation of Earth, which helps create circular flows. Oceans play a critical role in the overall weather patterns of our planet. Storms are ultimately generated by moisture in the atmosphere, and evaporation from the oceans is the prime source of such moisture. Oceans respond less dramatically to changes in solar energy than land does, so the temperature over a given patch of ocean is far more stable than one on land.

Life

The presence of life on Earth is, as far as we know, unique. The origin of life on Earth is not fully understood, but scientists believe amino acids, the essential building blocks of life, formed in the primordial oceans billions of years ago. Over eons, these building blocks combined and evolved into higher and higher life-forms.

Life has existed on dry land only for the most recent 10 percent of Earth's history, since about 385 million years ago. Once life got a foothold beyond the oceans, however, it spread rapidly. Within 200 million years, forests spread across the continents and the first amphibians evolved into dinosaurs. Mammals became dominant after the demise of the dinosaurs 65 million years ago. Only in the last 2 million years, that is, 0.05 percent of Earth's history, have humans appeared.

[See also Africa; Asia; Antarctica; Atmosphere, composition and structure; Australia; Cartography; Earthquake; Earth science; Earth's interior; Europe; Geologic time; Geology; Hydrologic cycle; Moon; North America; Ocean; Paleontology; Plate tectonics; South America; Solar system; Sun; Volcano; Weather ]

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earth (in geology and astronomy)

earth, in geology and astronomy, 3rd planet of the solar system and the 5th largest, the only planet definitely known to support life. Gravitational forces have molded the earth, like all celestial bodies, into a spherical shape. However, the earth is not an exact sphere, being slightly flattened at the poles and bulging at the equator. The equatorial diameter is c.7,926 mi (12,760 km) and the polar diameter 7,900 mi (12,720 km); the circumference at the equator is c.24,830 mi (40,000 km). The surface of the earth is divided into dry land and oceans, the dry land occupying c.57.5 million sq mi (148.9 million sq km), and the oceans c.139.5 million sq mi (361.3 million sq km). The earth is surrounded by an envelope of gases called the atmosphere, of which the greater part is nitrogen and oxygen.

The Geologic Earth

Knowledge of the earth's interior has been gathered by three methods: by the analysis of earthquake waves passing through the earth (see seismology), by analogy with the composition of meteorites, and by consideration of the earth's size, shape, and density. Research by these methods indicates that the earth has a zoned interior, consisting of concentric shells differing from one another by size, chemical makeup, and density. The earth is undoubtedly much denser near the center than it is at the surface, because the average density of rocks near the surface is c.2.8 g/cc, while the average density of the entire earth is c.5.5 g/cc.

The Earth's Crust and the Moho

The outer shell, or crust, varies from 5 to 25 mi (8 to 40 km) in thickness, and consists of the continents and ocean basins at the surface. The continents are composed of rock types collectively called sial, a classification based on their densities and composition. Beneath the ocean basins and the sial of continents lie denser rock types called sima. The sial and sima together form the crust, beneath which lies a shell called the mantle. The boundary between the crust and the mantle is marked by a sharp alteration in the velocity of earthquake waves passing through that region. This boundary layer is called the Mohorovičić discontinuity, or Moho.

The Earth's Mantle

Extending to a depth of c.1,800 mi (2,900 km), the mantle probably consists of very dense (average c.3.9 g/cc) rock rich in iron and magnesium minerals. Although temperatures increase with depth, the melting point of the rock is not reached because the melting temperature is raised by the great confining pressure. At depths between c.60 mi and c.125 mi (100 and 200 km) in the mantle, a plastic zone, called the asthenosphere, is found to occur. Presumably the rocks in this region are very close to melting, and the zone represents a fundamental boundary between the moving crustal plates of the earth's surface and the interior regions. The molten magma that intrudes upward into crustal rocks or issues from a volcano in the form of lava may owe its origin to radioactive heating or to the relief of pressure in the lower crust and upper mantle caused by earthquake faulting of the overlying crustal rock. Similarly, it is thought that the heat energy released in the upper part of the mantle has broken the earth's crust into vast plates that slide around on the plastic zone, setting up stresses along the plate margins that result in the formation of folds and faults (see plate tectonics). The lower mantle, between c.410 and 1,800 mi (660 to 2,900 km), consists largely (70%) of high-density magnesium iron silicate called bridgmanite, believed to be the most abundant mineral on earth.

The Earth's Core

Thought to be composed mainly of iron and nickel, the dense (c.11.0 g/cc) core of the earth lies below the mantle. The abrupt disappearance of direct compressional earthquake waves, which cannot travel through liquids, at depths below c.1,800 mi (2,900 km) indicates that the outer 1,380 mi (2,200 km) of the core are molten. The inner 780 mi (1,260 km) of the core are solid, and the innermost 190 mi (300 km) of that may be almost pure iron; the crystals of the innermost portion appear to be aligned along the plane of the equator, but those of the rest of the inner core appear to be aligned along the plane of the axis. The outer core is thought to be the source of the earth's magnetic field: In the "dynamo theory" advanced by W. M. Elasser and E. Bullard, tidal energy or heat is converted to mechanical energy in the form of currents in the liquid core; this mechanical energy is then converted to electromagnetic energy, which we see as the magnetic field. The magnetic field undergoes periodic reversals of its polarity on a timescale that ranges from a few thousand years to 35 million years. The last reversal occurred some 780,000 years ago.

The Astronomical Earth

Of the planets, only Mercury and Venus are nearer to the sun; the mean distance from the earth to the sun is c.93 million mi (150 million km).

Rotation and Revolution

The earth rotates from west to east about a line (its axis) that is perpendicular to the plane of the equator and passes through the center of the earth, terminating at the north and south geographical poles. The period of one complete rotation is a day; the rotation of the earth is responsible for the alternate periods of light and darkness (day and night). The earth revolves about the sun once in a period of a little more than 3651/4 days (a year). The path of this revolution, the earth's orbit, is an ellipse rather than a circle, and the earth is consequently nearer to the sun in January than it is in July; the difference between its maximum and minimum distances from the sun is c.3 million mi (4.8 million km). This difference is not great enough to affect climate on the earth.

The Change in Seasons

The change in seasons is caused by the tilt of the earth's axis to the plane of its orbit, making an angle of c.66.5°. When the northern end of the earth's axis is tilted toward the sun, the most direct rays of sunlight fall in the Northern Hemisphere. This causes its summer season. At the same time the Southern Hemisphere experiences winter since it is then receiving indirect rays. Halfway between, in spring and in autumn, there is a time (see equinox) when all parts of the earth have equal day and night. When the northern end of the earth's axis is tilted away from the sun, the least direct sunlight falls on the Northern Hemisphere. This causes its winter season.

The Origin of the Earth

The earth is estimated to be about 4.54 billion years old, based on radioactive dating of lunar rocks and meteorites, which are thought to have formed at the same time. The origin of the earth continues to be controversial. Among the theories as to its origin, the most prominent are gravitational condensation hypotheses, which suggest that the entire solar system was formed at one time in a single series of processes resulting in the accumulation of diffuse interstellar gases and dust into a solar system of discrete bodies. The generally accepted theory of the moon's formation hypothesizes that the early earth was impacted by a Mars-sized object, and that the collision ejected material that later formed the moon. Older and now generally discredited theories of the earth's formation invoked extraordinary events, such as the gravitational disruption of a star passing close to the sun or the explosion of a companion star to the sun.

Bibliography

See R. F. Flint, The Earth and Its History (1973); H. Jeffreys, The Earth (6th ed. 1976); F. Delobeau, The Environment of the Earth (1976); W. R. Brown and N. D. Anderson, Earth Science (rev. ed. 1977); D. Attenborough, The Living Planet (1985); R. Fortey, Earth (2004).

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Earth

133. Earth

See also 85. CLIMATE ; 134. EARTHQUAKES ; 142. ENVIRONMENT ; 143. EQUATOR ; 178. GEOGRAPHY ; 179. GEOLOGY ; 235. LAND ; 318. PLANETS ; 377. SOIL .

biosphere
that part of the earths surface where most forms of life exist, specifically those parts where there is water or atmosphere.
chthonic, chthonian
having to do with the underworld.
cosmosphere
a hollow glass globe for depicting the position of the earth in relation to the fixed stars at a given time.
diastrophism
the process of movement that causes the earths crust to form continents, mountains, oceans, etc. diastrophe , n. diastrophic , adj.
epeirogeny, epeirogenesis
the vertical movement or tilting of the earths crust, affecting broad expanses of continents. epeirogenic , epeirogenetic , adj.
geochronology
the branch of geology that describes the past in terms of geologic rather than human time. geochronologist , n. geochronologic , geochronological , adj.
geodynamics
the science of the forces at work within the earth. geodynamic , adj.
geogony
a theory or science about the formation of the earth. geogonic , adj.
geolatry
Rare. worship of the things of the earth or of the earth itself.
geology
the science that studies the physical history of the earth, the rocks of which it is composed, and the changes the earth has undergone and is undergoing. geologist . n. geologic , geological , adj.
geomalism
the tendency of organisms, under the influence of gravity, to be symmetrical. geomalic , adj.
geomancy
a form of divination that analyzes the pattern of a handful of earth thrown down at random or dots made at random on paper. geomancer , n.
geomorphology
the branch of geology that studies the form of the earths surface. geomorphologist , n. geomorphologic , geomorphological , adj.
geophagism, geophagy, geophagia
the eating of earthy matter, especially clay or chalk. geophagist , n. geophagous , adj.
georama
a large globe or sphere in which a spectator can stand and view a representation of the earths surface.
inclinometer
an instrument for measuring the inclination or dip of the earths magnetic force.
lithogenesy
the science of explaining the minerals of which the earth is composed, their origins, and the cause of their form and arrangement.
lithosphere
the solid part of the earth, as contrasted with the atmosphere and hydrosphere.
nutation
the periodic oscillation that can be observed in the precession of the earths axis and the precession of the equinoxes. See also 196. HEAD . nutational , adj.
obliquity
the inclination of the earths equator or the angle between the plane of the earths orbit and the plane of the equator (23°27). See also 25. ASTRONOMY . Also called obliquity of the ecliptic . obliquitous , adj.
planation
the formation of a flat or level surface by the process of erosion.
sphericist.
Rare a person who believes that the earth is round.
tellurist
a dweller on the earth. Also tellurian .

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Earth

Earth Third major planet from the Sun, and the largest of the four inner, or terrestrial planets. Water covers c.70% of the Earth's surface. This fact, and the Earth's average surface temperature of 13°C (55°F), makes it suitable for life. Continental land masses make up the other 30%. Earth has one natural satellite, the Moon. Like all the terrestrial planets, there is a dense core, rich in iron and nickel, surrounded by a mantle of silicate rocks. The thin, outermost layer of lighter rock is the crust, which can vary in depth from between 50km (30mi) – the thickest continental crust – to 5km (3mi) – the thinnest oceanic crust. The boundary between the crust and the mantle is called the Moho (Mohorovičić) discontinuity. The solid, inner core rotates at a different rate from the molten outer layers, and this, together with currents in the outer core, gives rise to the Earth's magnetic field. The crust and the uppermost mantle together form the lithosphere, which consists of tightly fitting slabs called plates. The plates, which float on a semi-molten layer of mantle called the asthenosphere, move with respect to one another in interactions called plate tectonics. See also atmosphere

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Earth

203. Earth

  1. Bona Dea goddess of earthly creatures. [Rom. Myth.: Parrinder, 48]
  2. Bona Mater Fauna, goddess of wildlife. [Rom. Myth.: Kravitz, 24]
  3. Demogorgon tyrant-genius of soil and life of plants. [Medieval Eur. Myth.: LLEI, I: 326]
  4. Dyava-Matar Hindu earthmother, equivalent of Demeter. [Hindu Myth.: Jobes, 480]
  5. Frigga Odins wife; symbolizes the earth. [Norse Myth.: LLEI, I: 328]
  6. Gaea goddess of the earth; mother of the mountains. [Gk. Myth.: Howe, 104]
  7. gnome ground-dwelling spirit in Rosicrucian philosophy. [Medieval Hist.: Brewer Dictionary, 468]
  8. Midgard region between heaven and hell where men live. [Norse Myth.: Wheeler, 242]
  9. Mother Nature epitome of the earth, especially its more benevolent phenomena. [Pop. Cult.: Misc.]
  10. Tapio Finnish woodland god; realm described in Sibelius Tapiola. [Music Hist.: Thompson, 2239]
  11. Tellus Mater in allegories of elements, personification of earth. [Art: Hall, 128]
  12. two circles linked symbol of earth as bride of heaven. [Christian Tradition: Jobes, 343]
  13. Vertumnus god of changing seasons. [Rom. Myth.: Kravitz, 58]

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earth

earth / ər[unvoicedth]/ • n. 1. (also Earth) the planet on which we live; the world: the diversity of life on earth. ∎  the surface of the world as distinct from the sky or the sea: it plummeted back to earth at 60 mph. ∎  the present abode of humankind, as distinct from heaven or hell: God's will be done on earth as it is in heaven. 2. the substance of the land surface; soil: a layer of earth. ∎  one of the four elements in ancient and medieval philosophy and in astrology (considered essential to certain signs of the zodiac). ∎  a stable, dense, nonvolatile inorganic substance found in the ground. 3. the underground lair or habitation of a badger or fox. PHRASES: come (or bring) back (down) to earth return or cause to return to reality after a period of daydreaming or excitement. like nothing on earth inf. very strange: they looked like nothing on earth. on earth used for emphasis: who on earth would venture out in weather like this?

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Earth

Earth The third planet in the solar system, outwards from the Sun. The mean distance of the Earth from the Sun is 149.6 × 106 km. This distance provides the standard ‘astronomical unit’ (AU) of measurement. The Earth has a mean radius of 6371 km, density of 5517 kg/m3, and a mass of 5.99 × 1027 g. The oceanic (5–7 km thick) and continental (40 km thick) crusts are separated by the Mohorovičić discontinuity from the silicate mantle, which extends to the Gutenberg discontinuity at 2900 km depth, and overlies a molten, iron-rich core. The oldest rocks are about 3980 million years old, and the Earth formed about 4600 million years ago.

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earth

earth OE eorðe = OS. ertha (Du. aarde), OHG. erda (G. erde), ON. jǫrð, Goth. airþa :- Gmc. *erþō, f. base *er-, appearing also in OHG. ero earth. ON. jǫrfi gravel, Gr. éraze on the ground, W. erw field.
Hence earth vb. †bury XIV; cover up with earth XVII. earthen XIII (see -EN3), whence earthenware XVII. earthly. OE. eorðliċ. earthquake XIV. earthy XVI; see -Y1.

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earth

earth earth mother (in mythology and primitive religion) a goddess symbolizing fertility and the source of life; in extended usage, an archetypally nurturing and maternal woman.
earth-shattering (in hyperbolic use) very important, shocking, or traumatic.

See also move heaven and earth, Mother Earth at mother, salt of the earth.

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Earth

Earth

all people on the globe, 1549; a group of foxes, 1575.

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Earth

EARTH

SeeZEMLYA

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earth

earthberth, birth, dearth, earth, firth, girth, mirth, Perth, worth •stillbirth • childbirth • afterbirth •Edgeworth • Hepworth • Ellsworth •Whitworth • halfpennyworth •Bosworth • jobsworth • Iorwerth

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Earth

EARTH

EARTH . "May the rain-maker water the Earth-Mother that she may be made beautiful to look upon." Thus opens a prayer to Awitelin Tsita, the earth divinity of the Zuni of New Mexico. The chant continues, "May the rain-makers water the Earth-Mother that she may become fruitful and give to her children and to all the world the fruits of her being that they may have food in abundance. May the Sun-Father embrace our Earth-Mother that she may become fruitful, that food may be bountiful, and that our children may live the span of life, not die, but sleep to awake with their gods" (Matilda Coxe Stevenson, "Ethnobotany of the Zuñi Indians," in Annual Report of the Bureau of Ethnology, Washington, D. C. 1915, p. 37). Many North American peoples revered the earth and remained deeply impressed by its sacredness. In the first years of the twentieth century, a Cheyenne explained to a visitor, "It is by the earth that we live. Without it we could not exist. It nourishes and supports us. From it grow the fruits that we eat, and the grass that sustains the animals whose flesh we live on; from it come forth, and over its surface run, the waters which we drink. We walk on it and unless it is firm and steadfast we cannot live" (George Bird Grinnell, "Tenure of Land among the Indians," American Anthropologist 9, 1907, p. 3).

Native Americans are not the only people to speak of the earth with intimacy and emotion. Throughout history and across cultures, people have clung to their images of the sacred earth. It is worthwhile and necessary to come to grips with these images. In the first place, they reveal a reality that remains veiled in any other terms. Furthermore, the study of the images of the earth bears directly on our understanding of the human condition as it has been plumbed by so much of the human family. In this article we review several important aspects of the earth, seen as a religious condition: earth as the source of life, earth as it appears at the beginning of time, the image of earth as the primal mother, and earth as the locus of regenerative life.

Source of Life

The cosmos is a reservoir of sacred forces. From a religious perspective, the earth is the clearest epiphany of an ensemble of sacred apparitions: soil, stones, trees, water, shadows, vegetation, and the jumbled landscape of the world. These form a single, living, cosmic unity. The soil, the earth, signifies this tangle of concrete vitalities. The earth is the foundation, the generative source, of every expression of existence. From the earliest records we possess of religious history, the earth, united with everything else that is, supports and contains all the life forms that reveal themselves to human beings. Earth is a tireless fount of existence. The lesson that the Cheyenne man taught his visitor is that the religious meaning of the earth remains indistinguishable from all the life that takes manifest form through the powers of the earth: mountains, forests, water, vegetation, and so on.

The Creative Role of Earth in the Beginning

A great number of myths describe a distant time when the earth produced or helped create life in the world. Among the many mythic themes, we call attention to five: androgyny, parthenogenesis, hierogamy, sacrifice, and emergence.

Androgyny: fullness of being

Androgyny is an ancient and widespread image of wholeness. Myths make clear that the meaning of androgyny goes beyond its overtly sexual manifestation to symbolize the perfection of a primordial, nonconditioned state of being. In fact, every beginning must start in the wholeness of being. Gods who manifested powerful aspects of the earth, especially divinities of vegetation and fertility, reveal traces of androgyny (cf. Nyberg, 1931, pp. 230ff., for bisexual earth divinities). These sources of holiness and power, such as Attis, Adonis, and Cybele in the Mediterranean world, portray the overfullness from which life springs. In cosmogonic myths, chaos often represents the perfect totality, the undifferentiated unity, on which all subsequent existence bases itself. In such circumstances, the creative role of the earth is obscure but discernible. The earth exists "in germ."

Such is the case in the Japanese texts recorded in the Kojiki and Nihongi. In the beginning, heaven and earth were inseparably mingled together. These male and female principles formed a perfect and androgynous totality within an egglike chaos. Eventually a tiny, amorphous island was precipitated out of the chaos. In this island was a reed, a development of the germ that first existed in the center of the cosmic egg. The reed was the first articulate transformation undertaken by the earth; it generated a number of gods. Later, when heaven and earth separated definitively from one another, they took on the human forms of a man and a woman, Izanagi and Izanami. The union of the two separate principles generated the world. When the woman died giving birth to the fire god, the deities of local places, hearths, and vegetation arose from her body. For the moment we focus our attention on the first stage of creation and on the incipient, androgynous being that embraces the sacred powers of the earth. These are not yet clearly defined, but they include all possibilities of life. As such, the divine androgyny in which the earth shares at the most primordial stage of creation is the ultimate ground of the realities that follow.

Parthenogenesis

According to Hesiod, "Earth [Gaia] herself first of all gave birth to a being equal to herself who could overspread her completely, the starry heaven [Ouranos] who was to present the blessed gods a secure throne forever" (Theogony 5126f.). This divine couple procreated the gods, the cyclopes, and a slew of mythical monsters, arrogant children with a hundred arms and fifty heads. Although Gaia finds no prominent place in the Homeric Hymns, one of them is addressed to her: "It is the earth I sing, securely enthroned, the mother of all things, venerable ancestress feeding upon her soil all that exists. To thee it belongs to give life to mortals and to take it from them" (Hymn to Earth 1ff.).

Ancient Greek traditions affirm that the earth existed before heaven, to whom the earth gave birth by parthenogenesis (i.e., without any male assistance or insemination; for treatment of parthenogenesis among Greek and other Mediterranean goddesses, see Uberto Pestalozza, Pagine di religione mediterranea, Milan, 1942, vol. 1, pp. 191ff.). Through such myths the power of the creative possibilities of the earth are portrayed as limitless. The motif of parthenogenesis by the primordial earth reappears in myths that account for all the species of animals and plants as having been born from the body of a primordial being, as well as in myths of virgin birth such as the Greek accounts of Hera who, alone and unaided by men, gave birth to Typhon, Hephaistos, and Ares. Izanami, the Japanese goddess of the earth, gave birth to a number of gods who issued from her own substance.

Hierogamy

Perhaps the most lavish and numerous myths depicting the role of the earth in creation are those that describe a marriage between heaven and earth, a hierogamy. Myths of this sort are reported from Oceania, Indonesia, Micronesia, Asia, Africa, Europe, and the Americas. When heaven encounters earth, life flows forth in innumerable forms. The union of heaven and earth is a fundamental act of creation; it generates life on a cosmic and biological scale. The Greek accounts about Gaia and the Japanese myths concerning Izanami show that the views of androgyny, parthenogenesis, and hierogamy are related and, on occasion, even overlap one another. All of these images, which are expressions of a coincidence of opposites, struggle to express the notion of creativity and of the cosmic fecundity of the earth. In the beginning of time, according to the Maori tradition, the sky, Rangi, and the earth, Papa, were locked together in a sexual union. Their children longed for the light of day. In the eternal darkness of their earthen womb, they plotted a way to separate their parents. Eventually, the children severed the bonds that tied heaven to earth and shoved their father into the air until light appeared.

According to Zuni accounts, the creator, Awonawilona, contained all being within himself. At first he existed alone in the universe, but then changed himself into the sun and produced two seeds from his own substance. With these he inseminated the waters. Under his warmth, the sea turned green and grew in size until it became the earth mother (Awatelin Tsita, the "fourfold-containing mother earth"), on the one hand, and the sky father (Apoyan Táchu, "all-covering father sky"), on the other. These cosmic twins embraced in union to produce the countless numbers of creatures. After many complications, the sun and the first ancestors he created managed to free the creatures germinating in the dark womb of the earth. Previously they had crawled over one another like reptiles, hissing and spitting out indecent words. Eventually, when the sky was lifted off the earth, these children escaped along a ladder to freedom and light (Frank Hamilton Cushing, "Outlines of Zuñi Creation Myths," in Annual Report of the Bureau of American Ethnology, Washington, D. C., l896, pp. 379384).

In myths of hierogamy, a sacred union with heaven, often symbolized by lightning, hail, or rain, is indispensable to the fruitfulness of the earth. It also serves as the model of fruitful human marriage. Hierogamy explains creation from some primordial whole that precedes it. The separation of heaven from earth is the first cosmogonic act, a fundamental shearing of primordial unity. In this widely known mythic drama, the fecundity of the earth with heaven is noticeably absent or sparsely distributed among the peoples of Australia, the Arctic, Tierra del Fuego, and the hunters and herders of North and Central Asia.

Sacrifice

In some myths of creation, the earth appears as a primordial victim of destruction (e.g., through conflagration, deluge, earthquake, petrification), especially through sacrifice, or even self-sacrifice. In such circumstances the fertility of the earth is never suppressed, for from the immolated or dismembered remains spring the species of plants, animals, linguistic groups, or races of humankind. The mystery of the creation of edible plants through the sacrifice of a goddess of the soil or earth was reenacted through agrarian rituals.

Most often, ritual sacrifices associated with the fertility of the soil were symbolic. In some cases, however, we possess reports of the actual sacrifice of living human victims. Such was the case, for example, among the Khonds of early nineteenth-century India. The Khond community, a Dravidian tribe inhabiting the hills of Orissa, a province of southern Bengal, bought a meriah, a voluntary victim who lived in the community for years, married, and fathered children. In the days preceding his sacrifice the meriah was ritually identified with the sacrificed divinity. The community danced in reverence around him. The victim was led in procession from the village to the virgin forest, the location of sacrifice. Participants anointed him and decorated him with flowers. They called upon the earth god, Tari Pennu (or Bera Pennu): "O God! We offer the sacrifice to you. Give us good crops, seasons, and health" (Frazer, 1926, p. 389). In front of representatives from every village in the vicinity, the meriah was slain, and a priest distributed fragments of the sacrificed body. These pieces were brought to the villages and ceremonially buried in the fields. The remains were burned so that the ashes could be spread over plowed fields to guarantee a good harvest.

In connection with the sacredness of the earth, the Aztec of central Mexico also performed acts of ritual sacrifice and dismemberment. When plants first sprouted, people sought the "god of the maize," a new shoot that was brought home, revered, and furnished with food offerings. That evening the new sprout was carried to a temple. The goddess of maize was honored by three different female age-groups. When the crop was ripe, the community celebrated a sacrifice in which a young girl represented Xilonen, the goddess of the new maize. After the young woman was sacrificed, the new crop could be consumed as food. Two months later, at the end of the harvest, another woman, representing the goddess Toci, was beheaded in sacrifice. A priest wore the flayed skin of the victim; another ritual specialist fashioned a mask from the victim's thigh. The masked participant played the role of a woman in childbirth in the harvest ritual.

These sacrifices ritually repeat the creation scenario in which the violent death of a primordial earth (e.g., through flood, fire, or violent self-sacrifice) gave rise to new forms, especially plants. Cut to pieces, the victim's body is identified with the mythic being whose death gave life to the cereal grain.

Emergence

We have seen how the earth figures largely in the creation of cosmic structures, as well as plant and animal life. A large number of myths emphasize the role of the earth in the origins of human life. As mentioned above in the opening scenes of the Zuni creation account reported by Cushing, the solitary creator became the sun and impregnated the great waters with two seeds from his own substance. These germs of men and of other creatures eventually hatched in the darkness. Pośhayank'ya, the great sage (who perhaps represents the nocturnal sun), then emerged from the foamy body of the earth mother, who possessed four wombs, one on top of another. It was in the deepest of these womb-caverns that all creatures dwelled in the beginning. For the first time, Pośhayank'ya pleaded with the sun father to liberate humanity from the dank and crowded bowels of the earth. In order to deliver the forms of life from the obscure and indistinct conditions of its fertile matrix, the sun father began another round of creation, but this time he aimed to produce intelligent beings who could find their way out of the dark, uterine hold of life-engendering earth. These beings would have the freedom that comes from the knowledge of magical power and ritual.

For a second time the sun father inseminated the foamy earth mother to produce twins. The twins sliced open the mountains and slipped into the subterranean darkness. With their warm breath they hastened the growth of a climbing plant, enabling it to break through to the light above. They then fashioned a ladder from its stalk, thus permitting the creatures to ascend from the lowest cavern into the second chamber. The beings who stayed behind or fell along the way became terrible monsters, creatures of the deep. Step by step, the twins provided the plant-ladder to grow and led the earthly pilgrims toward open space and heavenly light. At each stage, the people grew in wisdom, and humanity multiplied along the way, filling up whatever space was made available in the earth by the twins. Eventually, the twins led out, one after another, six distinct groups of people, the ancestors of the six human races. They emerged on the surface of the earth still bearing signs of their fetal existence in the ground: their toes were webbed and their ears, like those of bats and other creatures of the night, were attached to their heads by large membranes. They could not yet stand erect but crawled on their bellies like lizards or hopped like frogs.

The Caniengas Mohawk, an Iroquois group, also reported that humans once dwelled in the dark womb of the earth, without sunlight and in strange form. One day, during a hunt, one of the intraterrestrials accidentally discovered a hole that led to the surface of the earth. On the surface, this huntsman captured a deer. Drawn by the good-tasting game and the fine countryside, the subterranean creatures decided to emerge into the light of day. Only the groundhog remained in the earth.

Similarly, referring to the Lenni Lenape or Delaware Indians, the nineteenth-century scholar John Hockewelder remarked that "Indian mythologists are not agreed as to the form in which they existed while in the bowels of the earth. Some assert that they lived there in a human shape, while others, with greater consistency, maintain that their existence was in the form of certain terrestrial animals, such as the groundhog, the rabbit, and the tortoise" (cited in Frazer, 1926, p. 427).

These myths of emergence from the earth illustrate to what extent the earth is seen as a mother. In fact, the gestation of the fetus and the act of parturition are viewed as recapitulations of the cosmic birth of humankind and the creation of life in general, when humans emerged from the deepest chambers of the earth. Within the earth humanity lived an embryonic existence; for that matter, all the forms of creation existed as embryos within the earth. All living beings passed through the various stages of development in a "ripening" process that has not yet come to completion. For that reason the fruits of the earth reflect many different degrees of transmutation. Some Indian minerological tracts, for example, describe the diamond as "ripe" (pakka ), whereas crystal is "unripe" (kacca ), and the emerald, still wrapped in its stone womb, is only an embryo. In the same way, base metals and unrefined ores are not yet fully "ripe," but human smiths and alchemists may imitate, hasten, and complete the powerful functions of the earth mother.

This passage from the darkness of unconscious and preformal life to articulate form through emergence becomes a model for many human activities. When cultures wish to create something new, restore something worn, or regenerate a being, they reenact the pattern that was powerful enough to produce life in the first place. The act of procreation and birth of individual human beings in a culture is considered a reenactment of the primordial drama of emergence. The condition of the unborn child parallels the preexistence of humanity in the womb of the earth. Every fetal child relives the primal experience of humanity though its signs (darkness, water, enclosure, larval form, etc.). In other words, because the emergence myth is known, cultures recognize that every individual possesses a firsthand experience of the entire significant history of humanity. The human mother and her fertile powers are brought completely within the compass and sacredness of the great earth mother.

Mother Earth

Across the face of the globe, people cling to the belief that human beings were born from the earth. In some cases, human maternity is believed to result from the direct insertion of a child, an earthling, into a human woman's womb (whether in the form of a seed, an ancestral soul, or a miniature fetus). Up until the moment of its translocation into the human womb, the child had lived an embryological existence in the earthin a cave, well, fissure, or tree. In Lithuania, for example, children were said to come from springs, lakes, or hills intimately associated with Zemyna, the earth mother, for she alone was responsible for the creation of new beings (Haralds Biezais, Die Hauptgöttinnen der alten Letten, Uppsala, 1955, pp. 338342).

In many societies, the presence of a child in a mother's womb is attribued to her contact with some animal, stone, or other object. Whatever role the father and his sexual union with the mother might play, the fertility of the earth as the primordial mother is directly responsible for human motherhood and offspring. In such a setting of beliefs, human beings are, in a profound sense, people of their native land. Like the first humans in the earth, each new generation of children first lives among the rocks or in chasms. Aquatic animals such as frogs, crocodiles, fish, swans, or storks then bring them and place them magically in their mothers' wombs. Here again, fecund earth, the fertility of cosmic being, is represented by specific fruits or forms that take life from her (e.g., mountains, fertility stones, the waters of grottoes or springs, animals). A human mother simply receives children in their embryonic state. She is a container that helps the larval life of the earth attain a specifically human form. The belief is that the subterranean womb is the true fons et origo of embryological life, and once that is understood, the religious beliefs and practices described below make sense.

Memories of life in the womb

The experiences of mystics and shamans may be compared with prenatal existence in the womb of the earth. The primordial dark night of the soul portrays the opacity of subterranean life before emergence onto the surface of the earth. The power of North American shamans, for example, sometimes depends on their extraordinary abilities to remember their prenatal life. The images they recall from life in the womb bear striking similarity to the chambers, fixtures, sounds, and sensations of the subterranean world. The Guayaki of Paraguay often consult pregnant women as diviners, since their unborn children reveal secrets and truths to them. Fetal children possess the power to know obscure facts because they relive the primordial experience of the divine twins. These, in the first utter darkness of chaos, knew the germinal possibilities of all subsequent life forms and experienced them at first hand, in the darkness, before they pursued their diverse historical destinies.

At times the cultural community longs to return to the womb of the earth mother. The Yaruro people of Venezuela revered their great mother, who lived in the remote area of Kuma in the east, where the dead go. In the late 1930s, the Yaruro expressed the desire to reenter the realm of their mother in order to be reborn into the paradisal existence that preceded life and the arrival of colonial invaders (Vicenco Petrullo, The Yaruros of the Capanaparo River, Venezuela, Bureau of American Ethnology Bulletin 123, Washington, D. C., 1939, pp. 226ff.).

Labyrinths

The image of the earth as mother (with openings to the world in the form of galleries, mines, grottoes, and caves) and the desire to return to the embryonic stage of existence in the womb explain why the labyrinth can be an image of the body of the earth mother. The labyrinth, or meandering underground cavern, was an initiatory arena as well as a place to bury the dead. Entering a labyrinth (among other religious motivations for doing so) amounted to a ritual return to the womb of the mother. Labyrinthine caves were the sites of initiation, funerals, and marriages. It is in the fruitful womb of the earth that new forms of life first quicken. The labyrinth dramatizes the difficulty of discovering the past back to the sources of limitless creativity.

Malekula funeral symbolism, for example, describes Tenes (or Le-he-he), a frightening female being who lies in wait for dead men's souls. She stands at the entrance to a cavern; in front of her, outlined on the ground, is the sketch of a labyrinth. As the dead soul approaches, she rubs out half of the design. If the deceased has been properly initiated, he will know the entire outline of the labyrinth and find his road easily to the afterlife; otherwise the woman will swallow him. The labyrinths that one finds drawn on the earth in Malekula teach the living the road to the land of the dead. That is, they provide the living with the initiatory key that enables them to return into the bowels of the earth mother (A. Bernard Deacon, "Geometrical Drawings from Malekula and the Other Islands of the New Hebrides," Journal of the Royal Anthropological Institute 64, 1934, pp. 132ff.; John Layard, "Totenfahrt auf Malekula," Eranos-Jahrbuch 5, 1937, pp. 242292).

Agrarian rites

Rites that mark significant moments in the agricultural calendar repeat what happened to the earth in mythical times. The mysteries of how life emerged from a germ hidden in an undifferentiated chaos, or was engendered in the sacred union between heaven and earth, or resulted from the violent death of divinities associated with the soil are reenacted in the rituals of the earth. Agricultural operations in the Andes, for example, are scheduled around the menstrual periods of Pachamama, Mother Earth. Special restrictions are observed at the times when Pachamama is "open," for the life of the community and the cosmos depend on her fertility.

Women usually play crucial roles in the rites associated with earthly fecundity. Insofar as women are symbolically assimilated with the land and insofar as agricultural work is homologous with the sexual act (so that the plow or spade is an emblem of the phallus, for example), women become epiphanies of the sacred power of the earth. The acts of women have worldly significance, for they channel the effects of the earth's ability to bear fruit and modulate its intensity. The Qurʾān declares, "Your wives are to you as fields" (2:223). The Śatapatha Brāhmaa (7.2.2.5) identifies the furrows of a plowed field with a vulva and the seeds sown in the furrow with semen. These ideas are widespread; they account for the prominent ritual role of women in agriculture. Many communities consider it auspicious if a pregnant woman sows the new seed; it augurs a good harvest, for the crops will grow apace with the fetus. Often women put the seed in the ground cleared by men, or women choose and store reservoirs of the fertile powers of the earth. Agricultural labor keeps one cognizant of the sacred origins of gardening; labor is the vehicle of meaning as well as the vehicle of its transmission from one generation to another.

For example, after the Canelos Quechua women of Ecuador have set a new field, they remain in it with their children and recount episodes from ancient myths about Nungui, the goddess of garden soil, whose power underlies all fertility. The neighboring women of the Jivaroan community also sing to Nungui at the time of planting. Nungui is short, fat, and black (characteristic features of many "dark virgins" or black madonnas associated with the soil). She forces crops to break through the surface of the earth by making them grow. Nungui dances at night in gardens that are well maintained; the new shoots of manioc are her dancing partners. Since plants tend to shrink during the daylight hours, Jivaroan women harvest them in the morning.

In a related ritual Jivaroan women ask Nungui for "babies," three red jasper stones (nantara ) whose hidden location in the earth is revealed to them by the goddess in dreams. The nantara contain the female souls of manioc plants. Women hide the stones in the earth and keep them dark with an overturned food bowl placed in the center of the garden. The stones carry out the role of Nungui's mystical child who, in the primordial past, helped women accomplish all the tasks of farming with a single magical word. The prescribed layout of the contemporary Jivaroan garden and the red "children-stones" hidden there remain as signs of the perfect garden that existed at the beginning of time. When the time arrives to plant manioc seedlings, Jivaroan women gather to sing to Nungui while squatting over the new slips. The woman gardener places the first manioc cutting against her vaginal opening and paints the plant red before placing it in the ground. The identification of the fertility of women with the fertility of the soil is thus complete and direct. When they finish planting the fields, women dance for five nights in a row in honor of Nungui and request that her presence spur on the growth of the plants (Michael J. Harner, The Jívaro: People of the Sacred Waterfalls, Garden City, N.Y., 1973, pp. 7076; Julian H. Steward and Alfred Métraux, "Tribes of the Peruvian and Ecuadorian Montaña," in Handbook of South American Indians, vol. 3, New York, 1948, p. 620).

The religious role of women, who are identified with the land, appears dramatically in ritual sexual unions performed in fields or in orgies with which the entire community punctuates the agricultural calendar. With these sacred acts, women and their partners commemorate the union of heaven and earth in order to stimulate the fruitfulness of the virgin soil. Communal sexual frenzy evokes the image of the divine couple during the confusion of the long cosmic night in the period before creation, or in their primal state within the cosmogonic egg. During orgies, the whole community celebrates this return to the undifferentiated state of the earth at the beginning of time. The custom of streaking naked across the earth to provoke the virility of the sky or of the fertilizing rains shows how rites associated with the earth break down the barriers between individuals, society, cosmic nature, and divine forms. The experience of society during orgy is that of seeds and primordial embryos. The community as a whole loses its articulate shape during the period of subterranean merging and disintegration that is an integral part of the process of germination. Individuality dissolves in the orgy, for neither law nor social form is maintained in the total fusion of sexes and emotions. As in the ritual of immersion in water, orgy undoes the structures of the community and identifies human life with the formless, precosmic chaos in the bowels of the earth before creation. Even when orgies are not literally carried out but are only staged as performances (e.g., phallic dances or parades, dancing between series of unmarried partners), the fruitfulness of life derived from the earth depends on the symbolic dissolution of norms through carousing, obscenity, debauchery, insult, or choreographic and choral union of bodies and voices normally held separate from one another. For example, it is in connection with the fertility of the earth that many of the so-called hadaka matsuri (literally, "naked festivals") celebrated throughout Japan find their meaning.

Lying on the soil

We have already seen that the conception and birth of human individuals are scaled-down versions of the creative process performed by the earth since the beginning of time. Human mothers repeat that sucessful first act by which life first appeared in the womb of the earth mother. For that reason, at the moment of birth, women from many cultures put themselves directly in touch with the earth and mimic her actions. In this way they partake as fully as possible of her powers and remain under her protection. In numerous societies women give birth in such a way as to deposit the child onto the earth, or else place the child on the soil immediately after birth. In some cases women in childbirth lie prostrate on the ground or move into the forest or fields. "To sit on the ground" was a common expression in ancient Egypt meaning to give birth (Nyberg, 1931, p. 133). Every authentic birth of an Aché of Paraguay repeats the first act of standing upright upon the primordial earth. The Aché birth rites include two moments: waa, a "falling" from the womb onto the soil, and upi, a "lifting up." The act of touching the earth introduces the child to the biotic condition shared by all animals and plants. By lifting him up from the earth, the mother repeats his transition from amorphous biological form to fully human staturejust as it was obtained by the primordial ancestors when they first emerged from the earth and stood upright upon it (Pierre Clastres, Chronique des Indiens Guayaki, Paris, 1972, pp. 1416). The earth must be the mother who gives birth to every true human being.

Placement on the soil was also an integral part of healing rites. Sick persons were restored to health when they were created anew, remade in the image of the ancestral beings in their primordial situation within the earth. The Huichol of Mexico, for example, when on pilgrimage to Wirikuta, their place of mythic origins, stop by pools of water that open into the creative depths of the earth. The healer asks his patients, especially barren women, to stretch out full-length on the ground, which is the powerful body of the primal mother. The rite of placing a newborn child on the earth existed in ancient China, where a dying person was also set on the soil. The earth represents the powers both of birth and of rebirth to a new existence. The powers of the earth determine whether the transitions of birth and death are valid and well accomplished (Granet, 1953, pp. 192198).

Death and Regeneration

As a form of regenerative darkness, the earth, in its sacredness and fertility, includes the reality of death. This was clear already in the myths of the sacrifice of a primordial divinity associated with the soil. The death of the god gives rise to life in new forms, especially that of plants. Life and death are simply two phases in the career of Mother Earth. In fact, "life" in the light of day consists of a hiatus, a brief period of detachment from the earth's womb. It is death that returns one to the primordial or eternal condition that existed before the cycle of life began.

Many of the terrifying aspects of the earth mother, in the form of the goddess of death or the recipient of violent sacrifices, are rooted in her status as the universal womb, the source of all life. Death itself is not annihilation, but rather the state of the seed in the bosom of the earth. This helps explain why the bodies of the dead are buried in fetal positions in so many cultures. These "embryos" are expected to come back to life. In some cases, as stated above, the dead reenact the experience of the earth mother herself, who was the first person to die (e.g., Izanami of Japanese mythology, who died giving birth to fire). In such circumstances, the negative depictions of the earth mother as the goddess of death portray her role in the sacrificial mode of existence that makes passage from one form to another possible. The ubiquitous sacrificial dimension of symbolic existence guarantees the unending circulation of life. "Crawl to the earth, your mother," proclaims the gveda (10.18.10). "You, who are earth I place you in the earth," is a funerary formula from the Atharvaveda (12.1.11, 12.1.14). The Kraho of Brazil make every attempt to transport a dying man back to the soil of his maternal village. The inscriptions on ancient Roman tombs illustrate the same desire to rest in one's native earth. The vitality and fecundity of the earth, its sacred power to generate life without end, assures the reappearance of the dead in a new living form.

The rich symbolism of the earth is not exhausted by the cosmogonies, agricultural feasts, or burial practices of archaic peoples or tribal societies. The earth remains a powerful image of the possibility of new life and radically new social existence. In contemporary religious movements of rebellion or revolution prompted by desperate and oppressive circumstances, the earth becomes a focal image of renewal (Bruce Lincoln, "'The Earth Becomes Flat': A Study of Apocalyptic Imagery," Comparative Studies in Society and History 25, 1983, pp. 136153; see also Werner Müller, Geliebte Erde: Naturfrömmigkeit und Naturhass im indianischen und europäischen Nordamerika, Bonn, 1972). In the eschatological or utopian visions of new regimes or revolutionary kingdoms the face of the earth will be renewed or the end of the world will intervene to impose a new and just order, symbolized by the leveling of mountains and the filling of valleys. All forms of life, without discrimination, will obtain easy and equal access to the plenteous vitality of the earth.

Cosmic Solidarity of Life

The religious imagery of the earth engenders a kinship among all forms of life, for they are all generated in the same matrix. The intimate relationship between earth and the human, animal, and vegetal life forms inheres in the religious realization that the life force is the same in all of them. They are united on the biological plane; their fates, consequently, are intertwined. Pollution or sterility on one level of existence affects all other modes of life. Because of their common origin, all life-forms constitute a whole. Unlike the sacredness of the sky, which appears vividly in the myths of the separation of the sky from the creaturely forms dependent on it, there is no rupture between the earth and the forms it engenders.

Furthermore, earth protects the existence of life in myriad forms, and safeguards against abuses (e.g., incest or murder) that threaten the good order of reproductive life. Ritual union between sexual partners and orgies celebrated in ceremony are restricted to decisive moments of the agricultural calendar. During the rest of the time, the earth mother is often a patroness of morality and a guardian of the norms conducive to fruitful existence. The earth punishes certain categories of criminals, especially adulterers, murderers, and sexual miscreants. In some cases, as in ancient Greece, the shedding of blood on the earth and incest could render the earth barren, with catastrophic consequences. Thus, in the opening of Sophocles' Oedipus Rex, a priest bewails the fate of Thebes because women suffer birth pangs without living issue and the fruits of the earth and the oxen in the fields are dying, as is the city itself.

Conclusion

The earth reveals the meaning and sacredness of life's ceaseless ability to bear fruit. This point comes home strongly in all the images we have examined. There is a tendency for agricultural divinities, active and dramatic, to draw attention from the primordial divinities of the soil. But in all the great goddesses who represent the capacities of agriculture and the fruitfulness of the tilled soil there exists the underlying presence of the earth as a whole, the sacredness of the physical place of life. It is true that the earth often appears in cosmogonic myths as a figure vaguer in outline than the more clearly delineated goddesses of specific crops or particular rites in the agricultural cycle. However, the role of the earth in the earliest stages of mythic history testifies to the abiding sacredness of life itself, regardless of the distinct forms that it may include. The myths of parthenogenesis, of the androgyny of the earth, of hierogamy, of the sacrifice of the primordial earth, and of emergence from the dark womb of the first times affirm the sacredness of the soil. That is, they disclose the meaning of its tireless creativity. That manifestation of the sacred in the form of the soil, whether as a general presence or divine figure, helps make sense of rituals and symbolic forms linked to the earth.

Descents into caves and grottoes, the imagery of subterranean embryos, scenarios of return to a prenatal existence, labyrinths, rites of swearing by the earth, deposition of the newborn on the earth or interment of the dead in earthen graves, the iconographic tradition of black madonnas, and the terrifying figures of great goddesses, as well as the stylized sexual orgies of agricultural feasts return the attention of the religious imagination to one of its most important sources: the inexhaustible powers of the universal procreator of life. Few images have generated such power within the religious imagination or held such a command over it throughout the course of human history. It is possible that the rise of the earth to primacy as a sacred form in the religious imagination was stunted by her sacred marriage with the sky and other male divinities (e.g., storm gods) who are important in agriculture. Nevertheless, the earth, especially in the image of the great mother, has never forfeited her role as the locus of life, the source of all forms, the guardian of children, and the womb where the dead await their rebirth.

See Also

Alchemy; Androgynes; Caves; Dismemberment; Hieros Gamos; Labyrinth; Nature.

Bibliography

Several fundamental works recommend themselves for their comprehensive coverage of the phenomenon, as well as for their insight. Although dated, these studies are still important and valuable: Albrecht Dieterich's Mutter Erde (Berlin, 1905); Theodor Nöldeke's "Mutter-Erde und Verwandtes bei den Semiten," Archiv für Religionswissenschaft 8 (1905): 161166; Ernst Samter's Geburt, Hochzeit und Tod (Berlin, 1911), pp. 120; Wolf Wilhelm Baudissin's Adonis und Esmun (Leipzig, 1911), esp. pp. 443ff. and 505ff.; James G. Frazer's The Worship of Nature (London, 1926), pp. 316440; Marcel Granet's "Le dépôt de l'enfant sur le sol," in his Études sociologiques sur la Chine (Paris, 1953), pp. 159202; Henri Théodore Fischer's Het heilig huwelik van hemel en aarde (Utrecht, 1929); Bertel Nyberg's Kind und Erde (Helsinki, 1931); Willibald Staudacher's Die Trennung von Himmel und Erde (Tübingen, 1942); Vittore Pisani's "La donna e la terra," Anthropos 3740 (19421945); 241253; Uberto Pestalozza's Religione mediterranea: Vecchi e nuovi studi (Milan, 1951), esp. pp. 191ff.; and Gerardus van der Leeuw's "Das sogenannte Hockerbegräbnis und der ägyptische Tjknw," Studi e materiali di storia delle religioni 14 (1938): 151167.

Mircea Eliade's Myths, Dreams, and Mysteries: The Encounter between Contemporary Faiths and Archaic Realities (New York, 1960), pp. 155189, and Patterns in Comparative Religion (New York, 1958), chaps. 7 and 9, deal with earth and agriculture and offer ample bibliograpies. For a discussion of the images of the goddess in relation to the sacredness of the earth, see Andrew Fleming's article "The Myth of the Mother-Goddess," World Archaeology 1 (October 1969): 247261, and The Book of the Goddess: Past and Present, edited by Carl Olson (New York, 1983), which deals with the role of the goddess in prehistory, Mesopotamia, Egypt, Greece, Rome, Canaanite-Hebrew culture, in Christianity, gnosticism, Hinduism, Buddhism, Japanese religion, Afro-American culture, Amerindian religions, and in contemporary thought and practice. Bibliographies for these topics are included on pages 251259. Mother Worship: Theme and Variations, edited by James J. Preston (Chapel Hill, N. C., 1982), presents several cases from the New World, Europe, South Asia, and Africa.

Jürgen Zwernemann's Die Erde in der Vorstellungswelt und Kultpraktiken der sudanischen Völker (Berlin, 1968) is an example of a study of the full range of earth symbolism in a single culture. A most thorough and penetrating study of the earth is Ana Maria Mariscotti de Görlitz's Pachamama Santa Tierra (Berlin, 1978), which examines the history of belief and practice surrounding the earth mother in the South American Andes. Olof Pettersson's Mother Earth: An Analysis of the Mother Earth Concepts according to Albert Dieterich (Lund, 1967) redresses some of the hasty generalizations of Dieterich.

New Sources

Berthrong, John, and Mary Evelyn Tucker, eds. Confucianism and Ecology: The Interrelation of Heaven, Earth, and Human. Cambridge, Mass., 1998.

Chapple, Christopher Key, and Mary Evelyn Tucker, eds. Hinduism and Ecology: The Intersection of Earth, Sky, and Water. Cambridge, Mass., 2000.

Cloud, Preston. Oasis in Space: Earth History from the Beginning. New York, 1988.

Cooper, David E., and Joy A. Palmer, eds. Spirit of the Environment: Religion, Value, and Environmental Concern. New York, 1998.

Elvin, Mark and Liu Ts'ui-jung. Sediments of Time: Environment and Society in Chinese History. Cambridge, Mass. 1998.

Emiliani, Cesare. Planet Earth: Cosmology, Geology, and the Evolution of Life and Environment. New York, 1992.

Girardot, N.J., James Miller, and Liu Xiaogan, eds. Daoism and Ecology: Ways within a Cosmic Landscape. Cambridge, Mass., 2001.

Gottlieb, Roger S., ed. This Sacred Earth: Religion, Nature, Environment. New York, 1996.

Hessel, Dieter T., and Rosemary Radford Reuther, eds. Christianity and Ecology: Seeking the Well-Being of Earth and Humans. Cambridge, Mass., 2000.

Wright, M. R. Cosmology in Antiquity. New York, 1995.

Mircea Eliade (1987)

Lawrence E. Sullivan (1987)

Revised Bibliography

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Earth

EARTH

In Biblical Literature

The earth is portrayed in the Bible as a flat strip (Isa. 42:5; 44:24) suspended across the cosmic ocean (Ps. 24:2; 136:6). It is supported on pillars (Ps. 75:4; Job 9:6) or props (Isa. 24:18; Prov. 8:29) and is evidently surrounded by a mountain range like the qār of Arabic folklore, to keep it from being flooded (Prov. 8:29; Job 26:10). The ultimate bounds of the earth known to the ancient Hebrews were India and Nubia (Esth. 1:1; cf. Zeph. 3:10). A similar conception of the earth was held by Herodotus (3:114) and is found in the Persian inscriptions of Darius. Sometimes, too, its furthermost inhabitants were thought to be the peoples who resided in remote lands north of Palestine – *Gog and Magog – a concept which finds a parallel among the Greeks. It was believed that the fertility of the earth could be affected by the misconduct of men. It was then said to be "polluted" (Heb. ḥanefah; Isa. 24:5). As a result of Adam's sin, the earth yields grain only when man puts heavy labor into it (Gen. 3:17–19), and for receiving the blood of Abel it was forbidden to "yield its strength" to Cain under any circumstances (Gen. 4:11–13). The idea that the land could be rendered infertile by having innocent blood shed upon it is widespread in other cultures, and probably stems from the notion that "the blood is the life" and, therefore, represents the outraged spirit of the murdered man who exacts vengeance until the crime is redressed or expiated. Bloodshed could likewise cause lack of rainfall (ii Sam. 1:21). Since it is usually a particular land, especially the Land of Israel, that is affected by misdeeds committed in it, such misconduct includes not only moral turpitude but also disobedience to divine commandments. For example, a famine ensued for several years as a result of David's taking a census, against the orders of God. According to Exodus 23:10–12, the land of Israel had to lie fallow every seventh year; according to Leviticus 25, every 50th year as well. This may be explained as a survival of the ancient belief that life is vouchsafed in seven-year cycles. Deuteronomy, which speaks of the seventh year only as one of debt remission (Deut. 15) and enjoins a public reading of the Torah to the pilgrims assembled in Jerusalem on the festival of Tabernacles of that year (Deut. 31:10–13), is believed to represent a late development. Among the gentiles particular lands were regarded as the estates, or inheritances, of their tutelary gods; in the Bible yhwh is the Lord of what would later be known as the universe, yet the land of Israel is the object of His special care (Deut. 11:12; 32:8–9; ii Sam. 20:19; Jer. 2:7; Ps. 79:1). In the apocryphal book of Ben Sira (17:17), the Lord parcels out the earth among "rulers," i.e., celestial princes, as an emperor might apportion his dominion among satraps. Conversely, waste places were deemed the natural habitat of demons (Isa. 34:13–14), and the winds which sweep the wilderness were depicted as howling monsters, just as in Arabic folklore the desert is called "howl-place" (yabāb; cf. Deut. 32:10). Earth, like sky, was sometimes called to serve as a witness in prophetic denunciations of the people (Deut. 4:26; 30:19; 31:28). This reflects a common ancient Near Eastern practice of invoking the earth and sky, along with the national and local gods, to witness covenants and treaties. There is no clear evidence in the Bible of any worship of the earth, even by apostate Israelites. However, a goddess named Arṣay, i.e., Ms. Earth, is mentioned in the Canaanite texts from Ras Shamra (Ugarit) as one of the brides of Baal, and the Phoenician mythographer Sanchuniathon (second quarter of the sixth cent. b.c.e.) speaks of a primordial woman, called Omorka, who was cut asunder by Belus (Baal) to make earth and heaven respectively. In the six-day scheme of creation described in the first chapter of Genesis, earth is said to have emerged on the third day (Gen. 1:9–11). It was originally watered not by rain but by a subterranean upsurge (Heb. ed; Gen. 2:5–6). It is not impossible that this picture was inspired by conditions that actually obtain in parts of Palestine where, before the onset of the early rains and the beginning of the agricultural cycle in autumn, the soil is moistened only by springs which burst forth at the foot of the hills. It is possible – though this must be received with caution-that the Hebrews shared with the Babylonians the notion that the geography of the earth had its counterpart aloft and that the portions of the heavens corresponded to terrestrial domains, for it is in terms of such a view that it may perhaps be possible to interpret the words of Balaam (Num. 24:17) about the star which is stepping out of Jacob (i.e., the region of the sky answering to the Land of Israel) and which is destined to smite the borders of Moab. It was held that at the end of the present era of the world, when a new dispensation was to be ushered in, the soil of the Land of Israel would undergo a miraculous renewal of fertility. A stream, like that which flowed through Eden, would issue forth (Zech. 14:8), and there would be a prodigious increase in vegetation and livestock.

Post-Biblical Literature

Ideas about the earth are elaborated in post-biblical literature. The earth is represented as resting on a primal foundation stone, which also forms the bedrock of the Temple. The navel, or center, of the earth is located at Zion, just as among the Samaritans it is located at the sacred Mt. Gerizim, and among the Greeks, at Delphi. Earth, like heaven, consists of seven layers superimposed upon one another. Its extent is reckoned in one passage of the Talmud (Ta'an. 10a) as equivalent to (roughly) 190 million square miles, and it is 1,000 cubits thick. In iv Ezra 6:42 it is said that six parts of it are habitable, and the seventh is covered by water. According to post-biblical sources, the earth is sheltered from the blasts of the south wind by the gigantic bird ziz, and, as in the Bible, it will become miraculously fertile in the messianic age (Ginzberg, Legends, s.v.). Earth's pristine fertility, it is said, was diminished through the sin of Adam, and its smooth surface was made rugged by mountains as a punishment for its having received the blood of Abel. When the new age dawns, it will again become level. Just as in the Greek myth the earth opened to rescue Amphiaraus, so in Jewish legend it hid the tender babes of Israel hunted by Pharaoh. It likewise swallowed up the vessels of the Temple, to conceal them when that edifice was destroyed. On the other hand, it engulfed the four generations of the offspring of Cain as an act of punishment; it also swallowed up the army massed against Jacob, the unfinished part of the Tower of Babel, and the city of Nineveh. However, it refused to receive the body of Jephthah who, as the result of a rash vow, had sacrificed his own daughter (ibid., s.v.).

bibliography:

A.J. Wensinck, Ideas of the Western Semites Concerning Navel of the Earth (1916); R. Patai, Adam ve-Adamah (1943); T.H. Gaster, Myth, Legend and Custom in the Old Testament (1969), 5, 6, 98(d), 103(c), 144, 188, 294.

[Theodor H. Gaster]

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Earth

Earth

Physical parameters of earth

The formation of Earth

Earths surface

Earths atmosphere and weather

Beyond the atmosphere

Life

Resources

Earth is a rocky ball orbiting the sun with its large natural satellite, the moon. Most of the Earths surface, about 70%, is covered with water. It has an atmosphere that consists mostly of nitrogen and oxygen with trace levels of water vapor, and supports lifethe only place in the universe known, so far, to do so. A complete revolution of Earth around the sun takes about one year, while a complete rotation on its axis takes one day. The surface of Earth is constantly changing, as the continents slowly drift about on the turbulent mass of partially molten rock beneath them, the mantle. Collisions between landmasses build mountains, and erosion (the movement of material by water and air) wears them down.

Physical parameters of earth

Earth is the third of eight planets in our solar system. It orbits the sun at a distance of about 93, 000, 000 mi (150, 000, 000 km), taking 365.25 days to complete one revolution. Earth is fairly small by planetary standards; its diameter of 7, 921 mi (12, 756 km) is only about one-tenth that of Jupiter. Its mass is 2.108× 1026 oz (about six trillion kg), and it maintains a stable elliptical orbit around the sun by moving at about 19 mi (30 km) per second. Its mean density is 5.5 grams per cubic centimeter (compared to 1 g/cm3for water). Unlike the major outer planets Saturn, Jupiter, Uranus, and Neptune, which are composed mainly of light gases, Earth is made of heavy elements such as iron and nickel, and is therefore much more dense. These characteristicssmall and denseare typical of the inner four rocky or terrestrial planets, Mercury, Venus, Earth, and Mars.

The formation of Earth

About 4.5 billion years ago, the sun was born from a contracting cloud of interstellar gas. The cloud heated as it shrank, until its central part blazed forth as the mature, stable star that exists today. As the sun formed, the surrounding gas cloud flattened into a disk. In this disk the first solid particles formed and then grew as they accreted additional matter from the surrounding gas. Soon sub-planetary bodies, called planetesimals, built up, and then they collided and merged, forming the planets. The high temperatures in the inner solar system ensured that only the heavy elements, those that form rock and metal, could survive in solid form.

Thus were formed the small, dense terrestrial planets. Hot at first due to the collisions that formed it, Earth began to cool. Its components began to differentiate, or separate themselves according to their density, much as the ingredients in a bottle of salad dressing will separate if allowed to sit undisturbed. To Earths core went the heavy abundant elements, iron and nickel. Outside the core were numerous elements compressed into a dense but pliable substance called the mantle. Finally, a thin shell of cool, silicon-rich rock formed at Earths surface: the crust, or litho-sphere. Formation of the crust from the initial molten blob took half a billion years.

Earths atmosphere formed as a result of outgas-sing of carbon dioxide from its interior, and accretion of gases from space, including elements brought to Earth by comets. The lightest elements, such as helium and most of the hydrogen, escaped to space, leaving behind an early atmosphere consisting of hydrogen compounds such as methane and ammonia as well as water vapor and nitrogen- and sulfur-bearing compounds released by volcanoes. Carbon dioxide was also plentiful, but was soon dissolved in ocean waters and deposited in carbonate rocks. As the gases cooled, they condensed, and rains inundated the planet. The lithosphere was uneven, containing highlands made of buoyant rock such as granite, and basins of heavy, denser basalt. Into these giant basins the rains flowed, forming the oceans. Eventually life forms appeared, and over the course of a billion years, plants enriched the atmosphere with oxygen, finally producing the nitrogen-oxygen atmosphere we have today.

Earths surface

Land

The lands of our planet are in a constant, though slow, state of change. Landmasses move, collide, and break apart according to a process called plate tectonics. The lithosphere is not one huge shell of rock, but is composed of several large pieces called plates. These pieces are constantly in motion, because Earths interior is dynamic, with its core still molten and with large-scale convective currents in the upper mantle. The continents move about like scum islands floating on boiling soup, bumping into each other and separating again. Between them, sheets of relatively short-lived oceanic crust arise from the mantle and sink again (or are pushed under by subduction) after at most about 200 million years. The giant furnace beneath all of us moves our land no more than a few centimeters a year, but this is enough to have profound consequences.

Consider North America. The center of the continent is the magnificent expanse of the Great Plains and the Canadian Prairies. Flat and wide is the land around Winnipeg, Topeka, and Amarillo. On the eastern edge, the rolling folds of the Appalachian Mountains grace western North Carolina, Virginia, and Pennsylvania. In the west, the jagged, crumpled Rockies thrust skyward, tall, stark, and snow-capped.

These two great ranges represent one of the two basic land-altering processes: mountain building. Two hundred million years ago, North America was moving east, driven by the restless engine beneath it. In a shattering, slow-motion collision, it rammed into what is now Europe and North Africa. The land crumpled, and the ancient Appalachians rose. At that time, they were the mightiest mountains on Earth. A hundred million years later, North America was driven back west. Now the western edge of the continent rumbled along over the Pacific plate, and about 80 million years ago, a massive spate of mountain building formed the Rockies.

During the time since the Appalachians rose, the other land-altering process, erosion, has been hard at work on them. Battered by wind and water, their once sheer flanks have been worn into the low, rolling hills of today. Eventually they will be goneand sometime long after that, so will the Rockies.

Mountain building can be seen today in the Himalayas, which are still rising as India moves northward into the underbelly of Asia, crumpling parts of Nepal and Tibet nearly into the stratosphere. Erosion rules in Arizonas Grand Canyon, which gradually is deepening and widening as the Colorado river slices now into ancient granite two billion years old. In time, the Canyon too will be gone.

This unending cycle of mountain building (caused by movement of the crustal plates) and erosion (by wind and water) has formed every part of Earths surface today. Where there are mountains, as in the long ranks of the Andes or the Urals, there is subterranean conflict. Where a crustal plate rides over another one, burying and melting it in the hot regions below the lithosphere, volcanoes rise, dramatically illustrated by Mt. St. Helens in Washington and the other sleeping giants that loom near Seattle and Portland. Where lands lie wide and arid, they are sculpted into long, scalloped cliffs, as one sees in the deserts of New Mexico, Arizona, and Utah. Without ever being aware of it, we humans spend our lives on the ultimate roller coaster.

Water

Earth is mostly covered with water. The mighty Pacific Ocean covers nearly half Earth; from the proper vantage point in space one would see nothing but water, dotted here and there with tiny islands, with only Australia and the coasts of Asia and the Americas rimming the edge of the globe.

The existence of oceans implies that there are large areas of the lithosphere that are lower than others. This is because the entire lithosphere rides on a pliable layer of rock in the upper mantle called the astheno-sphere. Parts of the lithosphere are made of relatively light rocks, while others are made of heavier, denser rocks. Just as corks float mostly above water while ice cubes float nearly submerged, the less dense parts of the lithosphere ride higher on the asthenosphere than the more dense ones. Earth therefore has huge basins, and early in the planets history these basins filled with water condensing and raining out of the primordial atmosphere. Additional water was brought to Earth by the impacts of comets, whose nuclei are made of water ice.

The atmosphere has large circulation patterns, and so do the oceans. Massive streams of warm and cold water flow through them. One of the most familiar is the Gulf Stream, which brings warm water up the eastern coast of the United States.

Circulation patterns in the oceans and in the atmosphere are driven by temperature differences between adjacent areas and by the rotation of Earth, which helps create circular, or rotary, flows. Oceans play a critical role in the overall energy balance and weather patterns of our planet. Storms are ultimately generated by moisture in the atmosphere, and evaporation from the oceans is the prime source of such moisture. Oceans respond less dramatically to changes in energy input than land does, so the temperature over a given patch of ocean is far more stable than one on land.

Earths atmosphere and weather

Structure of the atmosphere

Earths atmosphere is composed of nitrogen (78% oxygen (21%), and other gases (1%). It is only about 50 mi (80 km) from the ground to space: on a typical, 12 in (30 cm) globe the atmosphere would be less than 2 mm thick. The atmosphere has several layers. The most dense and significant of these is the troposphere; all weather occurs in this layer, and commercial jets cruise near its upper boundary, 6 mi (10 km) above Earths surface. The stratosphere lies between 6 and 31 mi (10 and 50 km) above, and it is here that the ozone layer lies. In the mesosphere and the thermosphere one finds aurorae occurring after eruptions on the sun; radio communications bounce off the ionosphere back to Earth, which is why you can sometimes pick up a Memphis AM radio station while you are driving through Montana.

The atmosphere is an insulator of almost miraculous stability. Only 50 mi (80 km) away is the cold of outer space, but the surface remains temperate. Heat is stored by the land and the atmosphere during the day, but the resulting heat radiation (infrared) from the surface is prevented from radiating away by gases in the atmosphere that trap infrared radiation. This is the well-known greenhouse effect, and it plays an important role in the atmospheric energy budget. It is fortunate for us that Earths climate is this stable. A global temperature decrease of two degrees could trigger the next advance of the current ice age, while an increase of three degrees could melt the polar ice caps, submerging every coastal city in the world.

Weather

Despite this overall stability, the troposphere is nevertheless a turbulent place. It is in a state of constant circulation, driven by Earths rotation as well as the constant heating and cooling that occurs during each 24-hour period.

The largest circulation patterns in the troposphere are the Hadley cells. There are three of them in each hemisphere, with the middle, or Ferrel cell, lying over the latitudes spanned by the continental United States. Northward-flowing surface air in the Ferrel cell is deflected toward the east by the Coriolis force, with the result that windsand weather systemsmove from west to east in the middle latitudes of the northern hemisphere.

Near the top of the troposphere are the jet streams, fast-flowing currents of air that circle Earth in sinuous paths. If you have ever taken a commercial plane flight, you have experienced the jet stream: eastbound flights get where they are going much faster than westbound flights.

Circulation on a smaller scale appears in the cyclones and anticyclones, commonly called low and high pressure cells. Lows typically bring unsettled or stormy weather, while highs mean sunny skies. Weather in most areas follows a basic pattern of alternating pleasant weather and storms, as the endless progression of highs and lows, generated by Earths rotation and temperature variation, passes by. This is a great simplification, however, and weather in any given place may be affected, or even dominated, by local features. The climate in Los Angeles is entirely different from that in Las Vegas, though the two cities are not very far apart. Here, local featuresspecifically, the mountains between themare as important as the larger circulation patterns.

Beyond the atmosphere

Earth has a magnetic field that extends tens of thousands of kilometers into space and shields Earth from most of the solar wind, a stream of particles emitted by the sun. Sudden enhancements in the solar wind, such as a surge of particles ejected by an eruption in the suns atmosphere, may disrupt the magnetic field, temporarily interrupting long-range radio communications and creating brilliant displays of aurorae near the poles, where the magnetic field lines bring the charged particles close to Earths surface.

Farther out, at a mean distance of about 248, 400 mi (400, 000 km), is Earths only natural satellite, the moon. Some scientists feel that Earth and the moon should properly be considered a double planet, since the moon is larger relative to our planet than the satellites of most other planets.

Life

The presence of life on Earth is unique, as far as we have yet been able to detect (although most of the universe has not been examined due to its remoteness). Uncrewed spacecraft have landed on Venus, Mars, and Saturns giant moon Titan, have parachuted into the atmosphere of Jupiter, and have orbited or flown close to every other planet in the solar system except the dwarf planet Pluto. The most promising possibility, Mars, yielded no unambiguous life signs to the automated experiments performed by the Viking spacecraft that landed there in 1976. Subsequent landings, as of 2006, have not been equipped to look for life chemistry or to examine Marss soils at high enough magnification to detect microscopic life. Nevertheless, most scientists believe that life is unlikely to be found on Mars. More promising, in some ways, are several moons of the outer planets, such as Europa. Europa and several other moons of Jupiter are now known to harbor subsurface oceans of warm water. Where liquid water exists, the chances for life are thought to be much higherperhaps low, but better than zero.

The origin of life on Earth is not understood, but a promising experiment was performed in 1952 that may hold the secret. Stanley Miller and Harold Urey simulated conditions in Earths early oceans, reproducing the surface and atmospheric conditions thought to have existed more than three billion years ago. A critical element of this experiment was simulated lightning in the form of an electric arc. Miller and Urey found that under these conditions, amino acids, the essential building blocks of life, had formed in their primitive sludge. Certainly this was a long way from humansor even an amoebabut the experiment

KEY TERMS

Core The innermost layer of Earths interior. The core is composed of molten iron and nickel, and it is the source of Earths magnetic field.

Erosion One of the two main processes that alter Earths surface. Erosion, caused by water and wind, tends to wear down surface features such as mountains.

Lithosphere The outermost layer of Earths interior, commonly called the crust. The lithosphere is broken into several large plates that move slowly about. Collisions between the plates produce mountain ranges and volcanism.

Mantle The thick layer of Earths interior between the core and the crust.

Mountain-building One of the two main processes that alter Earths surface. Mountain-building occurs where two crustal plates collide and crumple, resulting in land forms thrust high above the surrounding terrain.

Terrestrial planets Planets with Earthlike characteristics relatively close to the sun. The terrestrial planets are Mercury, Venus, Earth, and Mars.

Troposphere The layer of air up to 15 mi (24 km) above the surface of the Earth, also known as the lower atmosphere.

proved that the early Earth may have been a place where organic compounds, the compounds found in living creatures, could form.

Life first appeared on Earth soon after it cooled enough to support liquid water, about 4.6 billion years ago. For the first 4 billion years, life consisted only of single-celled organisms. For the last 600 million years, multicellular plants and animals have existed. Life has existed on dry land only for the most recent 10% of Earths history, since about 400 million years ago. Once life got a foothold beyond the oceans, however, it spread rapidly. Within 200 million years forests spread across the continents and the first amphibians evolved into dinosaurs. Mammals became dominant after the demise of the dinosaurs about 65 million years ago, and only in the last two million years have humans come onto the scene.

See also Antarctica; Cartography; Continental drift; Earth science; Earths magnetic field; Earthquake; Geologic time; Geology; Hydrologic cycle; Paleontology; South America; Volcano.

Resources

BOOKS

Botkin, Daniel B. and Edward A. Keller. Environmental Science: Earth as a Living Planet. New York: John Wiley & Sons, 2004.

Brownlee, Donald and Peter Ward. The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World. New York: Owl Books, 2004.

Knoll, Andrew H. Life on a Young Planet: The First Three Billion Years of Evolution on Earth. Princeton, NJ: Princeton University Press, 2004.

Seeds, Michael A. The Solar System. Belmont, CA: Brooks Cole, 2006.

Tarbuck, Edward J., et al. Earth Science. 11th ed. Upper Saddle River, NJ: Prentice Hall, 2005.

Jeffrey C. Hall

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Earth

Earth

Earth is our home planet . Its surface is mostly water (about 70%), and it has a moderately dense nitrogen-and-oxygen atmosphere that supports life—the only known life in the Universe. Rich in iron and nickel, Earth is a dense, rocky ball orbiting the Sun with its only natural satellite , the Moon . A complete revolution of the earth around the Sun takes about one year, while a rotation on its axis takes one day. The surface of Earth is constantly changing, as the continents slowly drift about on the turbulent foundation of partially molten rock beneath them. Collisions between landmasses build mountains ; erosion wears them down. Slow changes in the climate cause equally slow changes in the vegetation and animals inhabiting a place.

Physical parameters of Earth

Earth is the third of nine planets in our solar system . It orbits the Sun at a distance of about 93,000,000 mi (150,000,000 km), taking 365.25 days to complete one revolution. Earth is small by planetary standards; with a diameter of 7,921 mi (12,756 km), it is only one-tenth the size of Jupiter . Its mass is 2.108 × 1026 oz (about six trillion kg), and it must speed this huge bulk along at nearly 19 mi (30 km) per second to remain in a stable orbit . The mean density of our planet is 5.5 grams per cubic centimeter. Unlike the outer planets, which are composed mainly of light gases, Earth is made of heavy elements such as iron and nickel, and is therefore much more dense. These characteristics—small and dense—are typical of the inner four planets, or terrestrial planets.

It was not until 1957, when the first man-made satellite was launched, that humans could see Earth as a beautiful whole. It seemingly floats in empty space , a world distinguished first by its vast oceans and only secondarily by its landmasses, everywhere draped in white swirls of clouds . This is a planet in the most fragile ecological balance, yet resilient to repeated catastrophe. It is our home, and it bears close examination.


The formation of Earth

About 4.5 billion years ago, our Sun was born from a contracting cloud of interstellar gas. The cloud heated as it shrank, until its central part blazed forth as the mature, stable star that exists today. As the Sun formed, the surrounding gas cloud flattened into a disk. In this disk the first solid particles formed and then grew as they accreted additional matter from the surrounding gas. Soon sub-planetary bodies, called planetesimals, built up, and then they collided and merged, forming the planets. The high temperatures in the inner solar system ensured that only the heavy elements, those that form rock and metal , could survive in solid form.

Thus were formed the small, dense terrestrial planets. Hot at first due to the collisions that formed it, Earth began to cool. Its components began to differentiate, or separate themselves according to their density, much as the ingredients in a bottle of salad dressing will separate if allowed to sit undisturbed. To Earth's core went the heavy abundant elements, iron and nickel. Outside the core were numerous elements compressed into a dense but pliable substance called the mantle. Finally, a thin shell of cool, silicon-rich rock formed at Earth's surface: the crust, or lithosphere . Formation of the crust from the initial molten blob took half a billion years.

Earth's atmosphere formed as a result of outgassing of carbon dioxide from its interior, and accretion of gases from space, including elements brought to Earth by comets . The lightest elements, such as helium and most of the hydrogen , escaped to space, leaving behind an early atmosphere consisting of hydrogen compounds such as methane and ammonia as well as water vapor and nitrogen- and sulfur-bearing compounds released by volcanoes. Carbon dioxide was also plentiful, but was soon dissolved in ocean waters and deposited in carbonate rocks . As the gases cooled, they condensed, and rains inundated the planet. The lithosphere was uneven, containing highlands made of buoyant rock such as granite, and basins of heavy, denser basalt. Into these giant basins the rains flowed, forming the oceans. Eventually life forms appeared, and over the course of a billion years, plants enriched the atmosphere with oxygen , finally producing the nitrogen-oxygen atmosphere we have today.

Earth's surface

Land

The lands of our planet are in a constant, though slow, state of change. Landmasses move, collide, and break apart according to a process called plate tectonics . The lithosphere is not one huge shell of rock; it is composed of several large pieces called plates. These pieces are constantly in motion , because Earth's interior is dynamic, with its core still molten and with large-scale convective currents in the upper mantle. The giant furnace beneath all of us moves our land no more than a few centimeters a year, but this is enough to have profound consequences.

Consider North America . The center of the continent is the magnificent expanse of the Great Plains and the Canadian Prairies. Flat and wide is the land around Winnipeg, Topeka, and Amarillo. On the eastern edge, the rolling folds of the Appalachian Mountains grace western North Carolina, Virginia, and Pennsylvania. In the west, the jagged, crumpled Rockies thrust skyward, tall, stark, and snow-capped.

These two great ranges represent one of the two basic land-altering processes: mountain building. Two hundred million years ago, North America was moving east, driven by the restless engine beneath it. In a shattering, slow-motion collision, it rammed into what is now Europe and North Africa . The land crumpled, and the ancient Appalachians rose. At that time, they were the mightiest mountains on Earth. A hundred million years later, North America was driven back west. Now the western edge of the continent rumbled along over the Pacific plate, and about 80 million years ago, a massive spate of mountain building formed the Rockies.

During the time since the Appalachians rose, the other land-altering process, erosion, has been hard at work on them. Battered by wind and water, their once sheer flanks have been worn into the low, rolling hills of today. Eventually they will be gone—and sometime long after that, so will the Rockies.

Mountain building can be seen today in the Himalayas, which are still rising as India moves northward into the underbelly of Asia , crumpling parts of Nepal and Tibet nearly into the stratosphere. Erosion rules in Arizona's Grand Canyon, which gradually is deepening and widening as the Colorado river slices now into ancient granite two billion years old. In time, the Canyon too will be gone.

This unending cycle of mountain building (caused by movement of the crustal plates) and erosion (by wind and water) has formed every part of Earth's surface today. Where there are mountains, as in the long ranks of the Andes or the Urals, there is subterranean conflict. Where a crustal plate rides over another one, burying and melting it in the hot regions below the lithosphere, volcanoes rise, dramatically illustrated by Mt. St. Helens in Washington and the other sleeping giants that loom near Seattle and Portland. Where lands lie wide and arid, they are sculpted into long, scalloped cliffs, as one sees in the deserts of New Mexico, Arizona, and Utah. Without ever being aware of it, we humans spend our lives on the ultimate roller coaster.

Water

Earth is mostly covered with water. The mighty Pacific Ocean covers nearly half the earth; from the proper vantage point in space one would see nothing but water, dotted here and there with tiny islands, with only Australia and the coasts of Asia and the Americas rimming the edge of the globe.

The existence of oceans implies that there are large areas of the lithosphere that are lower than others. This is because the entire lithosphere rides on a pliable layer of rock in the upper mantle called the asthenosphere . Parts of the lithosphere are made of relatively light rocks, while others are made of heavier, denser rocks. Just as corks float mostly above water while ice cubes float nearly submerged, the less dense parts of the lithosphere ride higher on the asthenosphere than the more dense ones. Earth therefore has huge basins, and early in the planet's history these basins filled with water condensing and raining out of the primordial atmosphere. Additional water was brought to Earth by the impacts of comets, whose nuclei are made of water ice.

The atmosphere has large circulation patterns, and so do the oceans. Massive streams of warm and cold water flow through them. One of the most familiar is the Gulf Stream, which brings warm water up the eastern coast of the United States.

Circulation patterns in the oceans and in the atmosphere are driven by temperature differences between adjacent areas and by the rotation of Earth, which helps create circular, or rotary, flows. Oceans play a critical role in the overall energy balance and weather patterns of our planet. Storms are ultimately generated by moisture in the atmosphere, and evaporation from the oceans is the prime source of such moisture. Oceans respond less dramatically to changes in energy input than land does, so the temperature over a given patch of ocean is far more stable than one on land.


Earth's atmosphere and weather

Structure of the atmosphere

Earth's atmosphere is the gaseous region above its lithosphere, composed of nitrogen (78% by number), oxygen (21%), and other gases (1%). It is only about 50 mi (80 km) from the ground to space: on a typical, 12-in (30 cm) globe the atmosphere would be less than 2 mm thick. The atmosphere has several layers. The most dense and significant of these is the troposphere; all weather occurs in this layer, and commercial jets cruise near its upper boundary, 6 mi (10 km) above Earth's surface. The stratosphere lies between 6 and 31 mi (10 and 50 km) above, and it is here that the ozone layer lies. In the mesosphere and the thermosphere one finds aurorae occurring after eruptions on the Sun; radio communications "bounce" off the ionosphere back to Earth, which is why you can sometimes pick up a Memphis AM radio station while you are driving through Montana.

The atmosphere is an insulator of almost miraculous stability. Only 50 mi (80 km) away is the cold of outer space, but the surface remains temperate. Heat is stored by the land and the atmosphere during the day, but the resulting heat radiation (infrared) from the surface is prevented from radiating away by gases in the atmosphere that trap infrared radiation. This is the well-known greenhouse effect , and it plays an important role in the atmospheric energy budget. It is well for us that Earth's climate is this stable. A global temperature decrease of two degrees could trigger the next advance of the current ice age, while an increase of three degrees could melt the polar ice caps , submerging every coastal city in the world.


Weather

Despite this overall stability, the troposphere is nevertheless a turbulent place. It is in a state of constant circulation, driven by Earth's rotation as well as the constant heating and cooling that occurs during each 24-hour period.

The largest circulation patterns in the troposphere are the Hadley cells. There are three of them in each hemisphere, with the middle, or Ferrel cell, lying over the latitudes spanned by the continental United States. Northward-flowing surface air in the Ferrel cell is deflected toward the east by the Coriolis force , with the result that winds—and weather systems—move from west to east in the middle latitudes of the northern hemisphere.

Near the top of the troposphere are the jet streams, fast-flowing currents of air that circle Earth in sinuous paths. If you have ever taken a commercial plane flight, you have experienced the jet stream : eastbound flights get where they are going much faster than westbound flights.

Circulation on a smaller scale appears in the cyclones and anticyclones, commonly called low and high pressure cells. Lows typically bring unsettled or stormy weather, while highs mean sunny skies. Weather in most areas follows a basic pattern of alternating pleasant weather and storms, as the endless progression of highs and lows, generated by Earth's rotation and temperature variation, passes by. This is a great simplification, however, and weather in any given place may be affected, or even dominated, by local features. The climate in Los Angeles is entirely different from that in Las Vegas, though the two cities are not very far apart. Here, local features—specifically, the mountains between them—are as important as the larger circulation patterns.

Beyond the atmosphere

Earth has a magnetic field that extends tens of thousands of kilometers into space and shields Earth from most of the solar wind , a stream of particles emitted by the Sun. Sudden enhancements in the solar wind, such as a surge of particles ejected by an eruption in the Sun's atmosphere, may disrupt the magnetic field, temporarily interrupting long-range radio communications and creating brilliant displays of aurorae near the poles, where the magnetic field lines bring the charged particles close to the earth's surface.

Farther out, at a mean distance of about 248,400 mi (400,000 km), is Earth's only natural satellite, the Moon. Some scientists feel that the earth and the Moon should properly be considered a "double planet," since the Moon is larger relative to our planet than the satellites of most other planets.


Life

The presence of life on Earth is, as far as we know, unique. Men have walked on the Moon, and it seems certain there is no life on our barren, airless satellite. Unmanned spacecraft have landed on Venus and Mars and have flown close to every other planet in the solar system except Pluto . The most promising possibility, Mars, yielded nothing to the automated experiments performed by the Viking spacecraft that touched down there.

The origin of life on Earth is not understood, but a promising experiment was performed in 1952 that may hold the secret. Stanley Miller and Harold Urey simulated conditions in Earth's early oceans, reproducing the surface and atmospheric conditions thought to have existed more than three billion years ago. A critical element of this experiment was simulated lightning in the form of an electric arc . Miller and Urey found that under these conditions, amino acids, the essential building blocks of life, had formed in their primitive "sludge." Certainly this was a long way from humans—or even an amoeba—but the experiment proved that the early Earth may have been a place where organic compounds, the compounds found in living creatures, could form.

Life has existed on dry land only for the most recent 10% of Earth's history, since about 400 million years ago. Once life got a foothold beyond the oceans, however, it spread rapidly. Within 200 million years forests spread across the continents and the first amphibians evolved into dinosaurs. Mammals became dominant after the demise of the dinosaurs 65 million years ago, and only in the last two million years have humans come onto the scene.

See also Antarctica; Cartography; Continental drift; Earth science; Earth's magnetic field; Earthquake; Geologic time; Geology; Hydrologic cycle; Paleontology; South America; Volcano.


Resources

books

Beatty, J., and A. Chaikin. The New Solar System. Cambridge: Cambridge University Press, 1991.

Cater, John. Key to the Future: The History of Earth Science. New York: Routledge, 2002.

Hamblin, W. K., and E.H. Christiansen. Earth's Dynamic Systems. 9th ed. Upper Saddle River: Prentice Hall, 2001.

Hancock, P. L. and B. J. Skinner, eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Press, F., and R. Siever. Understanding Earth. 3rd ed. New York: W. H Freeman and Company, 2001.

periodicals

"The Dynamic Earth." Scientific American 249 (special issue, September 1983): 46–78+.

Haneberg, William C. "Determistic and Probabilistic Approaches to Geologic Hazard Assessment." Environmental & Engineering Geoscience 6, no. 3 (August 2000): 209–226.

Hoehler, T. M., B. M. Bebout, and D. J. Des Marais. "The Role of Microbial Mats in the Production of Reduced Gases on the Early Earth." Nature 412 (July 2001): 324–327.


Jeffrey C. Hall

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Core

—The innermost layer of Earth's interior. The core is composed of molten iron and nickel, and it is the source of Earth's magnetic field.

Erosion

—One of the two main processes that alter Earth's surface. Erosion, caused by water and wind, tends to wear down surface features such as mountains.

Lithosphere

—The outermost layer of Earth's interior, commonly called the crust. The lithosphere is broken into several large plates that move slowly about. Collisions between the plates produce mountain ranges and volcanism.

Mantle

—The thick layer of Earth's interior between the core and the crust.

Mountain-building

—One of the two main processes that alter Earth's surface. Mountain-building occurs where two crustal plates collide and crumple, resulting in land forms thrust high above the surrounding terrain.

Terrestrial planets

—Planets with Earth-like characteristics relatively close to the Sun. The terrestrial planets are Mercury, Venus, Earth, and Mars.

Troposphere

—The layer of air up to 15 mi (24 km) above the surface of the Earth, also known as the lower atmosphere.

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Earth

EARTH

In science and philosophy earth (German Erde, Greek ge) can refer to one in a set of primordial material elements (earth, air, fire, and water, for the Greeks; wood, fire, earth, metal, water, for the Chinese) and to the physical body on which humankind lives. As physical home, the Earth serves as the reflective horizon or framework for human self-awareness and as a contingent unity among the array of individual entities they encounter. The Earth, defined by an elemental earthiness of rock and soil, is that which grounds the identity of humans in both physical and psychological senses, independent of wherever they may venture in information networks or outer space, while serving as a fund of resources available for exploitation. The tensions between these various approaches are imaged in the diagrammatic icon of the atom and the photo of the blue planet taken from space: matter that is mostly space and a life-giving sphere that appears more water than rock and calls perhaps for technological management.

Earth Science and Engineering

As soil and matter, earth has become a distinctive object for science and technology. The material out of which all things are made has itself become subject to chemical processing, synthesis, and nuclear engineering. The scientific study of matter existing independent of humans has expanded to examining those new forms of matter intentionally and unintentionally designed by humans and the interactions between the two, especially insofar as they may impact on humans themselves. As a planet the Earth is a body in space with a stable orbit at a distance from the sun suitable for the origin and evolution of life. During its 4.56 billion years the Earth has given rise to an abundance of organisms, first in the sea, and then diversifying and evolving to occupy land and air. As recipient of heat energy from both the sun and its own core, the Earth is a site of dynamic terrestrial behavior. The seven major tectonic plates comprising its rocky outer crust diverge and then compensate through convergence; its land masses, ocean basins, islands, and other prominent features such as volcanoes, mountains, plains, and valleys have gone through continual development—producing new materials essential of life and humans. Hominids appeared on the Earth 7 million years ago and Homo sapiens about 200,000 years ago. Humans began to till the Earth about 10,000 years ago.

This early-twenty-first-century perspective on earth and the Earth sees them as dynamic complexities inviting examination and provoking manipulation. Especially with regard to the Earth, it is now perceived as a nexus of interactions between the solar system and its own atomic and subatomic foundations, as well as of exchanges between its own landmasses, oceans, atmosphere, and living organisms. Through earth system science these have in turn become, because of human technological powers and their commercial development, also subject to speculative engineering management. Earth system science is complemented by the possibilities of earth systems engineering and thus challenged to reflect ethically on both ends and means.

Philosophies of the Earth

The Earth has throughout human history been a focus of philosophizing, central to ethics, and a framework for self-understanding. For the Greeks, the Earth was implicated in their cosmology not only as planet and home of humanity, as focus of the gods who lived above its plane, and in relation to the heavens; its core constituent, earth, was also one of the four elements, earth, water, air, and fire. The Earth itself was a compound of the four elements. For the Chinese, the earth and heaven are the two forces responsible for engineering and completing nature and all its aspects. Earth and heaven also work together to create the five Chinese elements: wood, fire, earth, metal, and water. As an element, the Earth is located at the center and is the cauldron, with the other four elements located in the four outer directions, east, west, north and south. Earth is also the element of the "naked" animal, the human, of the actions is representative of "thought." The element earth is also associated with the sense of touch, the sound of singing, the organ of the spleen, and the virtue of good faith. There have been two related controversies about the place of the Earth within cosmological, metaphysical, and ethical visions: whether the Earth is the center of a given scheme of existence or is only an element in a vaster cosmos, and whether the earth is a site of corruption at a distance from a purer realm or is a unique locus of corporeal and spiritual development.

Plato approaches both issues in his atypical dialogue, the Timaeus. He describes an original Demiurge who takes the elements of earth, fire, air, and water and "out of such elements which are four in number, the body of the world was created, and it was harmonized by proportion, and therefore has the spirit of friendship; and having been reconciled to itself, it was indissoluble by the hand of any other than the framer" (33, c). This picture of the Earth as a model of balance, harmony, and fairness is complemented by a world soul infusing the world with a vitality and rationality of fair proportion: "The world became a living creature truly endowed with soul and intelligence by the providence of god" (30, c). The Earth as an entity in the cosmos is described as located at the center and surrounded by the moon, the sun, and five planets in circular orbits. This picture from the Timaeus is opposed by another from the Phaedo. There Plato writes of the "earth and the stones and all the places [as] corrupted and corroded, as things in the sea are by brine so that nothing worth mention grows in the sea, and there is nothing perfect there, one might say, but caves and sand and infinite mud and slime wherever there is any earth, things worth nothing" (110, b). He condemns the passions and senses for "nailing" people to the Earth that, by its attractive power, can "drunkenly" estrange human souls from their true home in the aether beyond (83, d). His emphasis on the immaterial nature of the soul and its kinship with the intelligible structure underlying reality leads to a condemnation of the earthly as tempting snare.

Aristotle, by contrast, observes the Earth and catalogues its differences in beings—animate and inanimate—embracing "the delight we take in our senses," especially the sense of sight as indicating that "this, most of all the senses, makes us know and brings to light many differences between things" (980, a). His vision of the Earth as a nexus of beings defined by their for sake of which—their purpose as fully actualized—working in concert with other beings' drive to actualization, renders a grandeur to the dynamism and wholeness of the Earth and the totality of its excellences fully realized. His cosmological vision in On the Heavens further emphasizes this foundation status because "the earth does not move and does not lie elsewhere than at the center." Aristotle's placing of the Earth at the center of the cosmos around which the sphere of the fixed stars daily rotates, carrying with it the spheres of the sun, moon, and planets, is the authority cited by Ptolemy (85–165 c.e.) in working out his plan of the Earth in relation to the heavens.

The shift in perspective known as the Copernican Revolution began when the Polish astronomer Nicolaus Copernicus (1473–1543) wrote his Little Commentary (1514). He argued that there was no one center to the universe, the Earth's center is not the center of the universe, the rotation of the Earth accounts for the apparent daily rotation of the stars, and the Earth revolves in a vast space. These ideas helped inaugurate the thinking that Galileo Galilei (1564–1642) would confirm a century later. This philosophy not only displaced the Earth from its central position in religious cosmologies, but made the planet itself into a composite of more basic materials to be analyzed and manipulated.

The Cartesian method of analysis led several European scientists in the 1860s to articulate how the basic constituents of all chemical compounds could be broken down into their simplest components. These elements, as measured and compared by their atomic weight, were arrayed in a chart, the periodic table, that both presented them sequentially (giving them an atomic number based on their atomic mass) and grouped them according to their electron configuration, which gives them similar chemical behavior such as the group of inert gases or that of alkali metals, for example. The table as presented in 1869 by the Russian chemist Dmitrii I. Mendeleev is still used with little revision other than filling in spaces left blank for predicted new elements.

Earths and Ethics

The approach to earth as a composite or collection of discrete units has informed one dominant modern philosophical perspective. Seen in terms of external relations among material constituents, this perspective tends toward a utilitarian approach to ethical problems. If the greatest number of people benefit from some alteration or use of an environment, or if some part of the environment which occurs naturally can be functionally replaced through technological advance, then utilitarianism allows for these alterations of the earth, even if they might involve a diminution in its diversity or degradations in its ecological viability. This approach has nevertheless promoted the rights of excluded social groups in arguments for environmental justice, as well as suggested that animals have rights as part of the earth (Singer 1990).

A contrasting philosophical perspective contends that the Earth has a distinct holistic identity, perhaps inseparably intertwined with the collective identity of humanity. Explorations of this option often rely on James Lovelock's Gaia: A New Look at Life on Earth (1979), in which he posited the Earth is an evolving, self-regulating organism. In this view, the planet through its temperature, gaseous constituents, minerals, acidity, and many other factors maintains a homeostasis by active feedback processes operating in the biota. Other philosophical views, while not seeing the planet itself as a living being, do envision human identity as internally related to aspects of the earth in such a way that these relationships themselves constitute the identity of both, such as in the work of Arne Ness, Dave Abram, Glen Mazis, or Freya Matthews. From such a perspective a utilitarian ethics fails to adequately safeguard either the Earth or humanity and all those parts of the biosphere due respect for their intrinsic work.

Returning to the question of the Earth as the horizon for humanity's sense of meaning and purpose, one path in philosophy is that first proposed by Friedrich Nietzsche in Thus Spoke Zarathustra (1883) and its claim that the nihilism of modern culture can only be undercut by a reevaluation of values and a reidentification of humanity as no disembodied spirit but as an animal of passion, body, sensuality, and reason—whose greatest challenge is to create value and meaning while obeying the injunction to "remain faithful to the earth." Edmund Husserl called the Earth the foundation [Boden] of the sense of being human and likened the planet to an ark that would always be with humanity as its abiding sense of identity no matter where humanity ventured.

For Martin Heidegger, humans open up a horizon for meaning and purpose through the way that art and other institutions open "the strife between earth and world," as he articulated in "the Origin of the Work of Art." The artist, like other creators, must initiate a dynamic struggle between the context of meaning and value, which makes up the "world" of various epochs and cultures with the opacity and resistance of the sheer materiality of the earth. The earth both anchors and occludes this birth of meaning, so it is literally "grounded" and yet never fully fathomable, but suggestive. In his analysis of the elements fire, water, air, and earth, Gaston Bachelard saw the Earth as the dimension which gives humanity a rootedness, and a sense of infinite depth, as well as a resistance against which meaning is forged in action. The resistance of the earth is the "partner of the will." Humans are motivated to create and shape in response to the earth. Differing visions and temperaments respond to the continuum of earth in its span from hardness to softness. Humanity is motivated to forge the earth into creations as well as struggle against earth's gravity towards flight.

Increasingly, too, there is a growing interchange of Western philosophy with global philosophical perspectives that suggests the inseparability of humanity and earth. These ideas include the Buddhist emphasis on the ontological interdependence of all living and nonliving beings expressed through the concept of "emptiness," which might be better evoked as the relativity among all beings, as well as the depiction of the Buddha's original inspiration to seek enlightenment after shedding tears at seeing the worms and insects cut up by the plows making furrows in the fields with the same grief he would have had for the death of his family. There is the Daoist sense of nonacting [Wu wei] in which the beings of the Earth act through humans or as the Way [Dao] itself is the dynamic interplay of the entities of the Earth—"the ten thousand things"—as well as the Earth itself as a larger field of energy. Within North America, there is the Native American sense that all beings are part of Mother Earth or the Great Spirit, living on turtle island, the community of two-legged, four-legged, and all other beings of the four directions.

A challenge ahead is whether these philosophical perspectives can integrated with earth system science and engineering at the micro and macro scales in which they are now being practiced in order to give some basis for ethical decision making and a coherent perspective.

GLEN A. MAZIS

SEE ALSO Air; Earth Systems Engineering and Management; Environmental Ethics; Fire; Gaia; Green Ideology; Nature; Water; Wilderness.

BIBLIOGRAPHY

Abram, Dave. (1996). The Spell of the Sensuous. New York: Random House.

Aristotle. (1941). The Basic Works of Aristotle. New York: Random House.

Bachelard, Gaston (2002). Earth and Reveries of Will. Dallas: Dallas Institute.

Connelly, Dianne M. (1994). Traditional Acupuncture: The Law of the Five Elements. Columbia: Traditional Acupuncture Institute.

Feng, Gia-Fu, and Jane English. (1972). Tao Te Ching. New York: Alfred A. Knopf.

Heidegger, Martin. (1971). Poetry, Language, Thought. New York: Harper and Row.

Luhr, James F. (2003). Earth. New York: DK Publishing.

Matthews, Freya. (2005). Rehabilitating Reality. Albany: State University of New York Press.

Mazis, Glen A. (2002). Earthbodies. Albany: State University of New York Press.

Naess, Arne. (1989). Ecology, Community and Lifestyle. Cambridge: Cambridge University Press.

Plato. (1961). The Collected Dialogues of Plato, ed. Edith Hamilton and Huntington Cairns. Princeton: Princeton University Press.

Singer, Peter. (1990 [1975]). Animal Liberation: A New Ethics for Our Treatment of Animals, 2nd edition. New York: New York Review.

Ward, Peter, and Donald Brownlee. (2003). Rare Earth: Why Complex Life is Uncommon in the Universe. New York: Copernicus Books.

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"Earth." Encyclopedia of Science, Technology, and Ethics. . Encyclopedia.com. 17 Aug. 2018 <http://www.encyclopedia.com>.

"Earth." Encyclopedia of Science, Technology, and Ethics. . Encyclopedia.com. (August 17, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/earth-1

"Earth." Encyclopedia of Science, Technology, and Ethics. . Retrieved August 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/earth-1

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http://www.chicagomanualofstyle.org/tools_citationguide.html

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