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); Earth—why 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.

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 life—the 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 ]

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) 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 Earth's Core

Thought to be composed mainly of iron and nickel, the dense (c.11.0) 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. It is thought, however, that the inner 780 mi (1,260 km) of the core are solid. 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 365 1/4 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 4.5 billion to 5 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).

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 earth’s 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 earth’s crust to form continents, mountains, oceans, etc. —diastrophe , n. —diastrophic , adj.

epeirogeny, epeirogenesis

the vertical movement or tilting of the earth’s 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 earth’s 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 earth’s surface.

inclinometer

an instrument for measuring the inclination or dip of the earth’s 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 earth’s axis and the precession of the equinoxes. See also 196. HEAD . —nutational , adj.

obliquity

the inclination of the earth’s equator or the angle between the plane of the earth’s 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 .

Earth (symbol ⨁ or ♁) The third planet from the Sun. At perihelion each January it is 147 099 590 km from the Sun, as against 152 096 150 km at aphelion in July. Seen from far off in space it has a strong blue coloration, caused by its atmosphere. The Earth is slightly ellipsoidal in shape (equatorial diameter 12 756 km, polar diameter 12 714 km). Its age is 4.57 × 10⁹ years.

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

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 Odin’s 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]

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?

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.

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.

earth Sometimes the created world (Matt. 6: 10) in contrast to heaven; or else the firm ground in contrast to the sea (Acts 4: 24); or it may designate the whole inhabited area and its population (Rev. 13: 3). In the OT the same word is sometimes to be translated ‘earth’, sometimes ‘world’, and it is not always clear which is more appropriate.

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.

Earth

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

EARTH

SeeZEMLYA

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