Geological Time Scale

views updated May 11 2018

Geological Time Scale

Geologic Time Scale
EraPeriodEpochSignificant EventsMillion Years Before Present
CenozoicQuartenaryHolocenerecorded human history, rise and fall of civilizations, global warming, habitat destruction, pollution mass extinction0.01
PleistoceneHomo sapiens, ice ages1.6
TertiaryPlioceneglobal cooling, savannahs, grazing mammals5.3
Mioceneglobal warming, grasslands, Chalicotherium24
Oligocene37
Eocenemodern mammals flourish, ungulates58
Paleocene66
MesozoicCretaceouslast of age of dinosaurs, modern mammals appear, flowering plants, insects144
Jurassichuge plant-eating dinosaurs, carnivorous dinosaurs, first birds, breakup of Pangea208
Triassiclycophytes, glossopterids, and dicynodonts, and the dinosaurs245
PaleozoicPermianPermian ends with largest mass extinction in history of Earth, most marine inverterbrates extinct286
Pennsylvanianvast coal swamps, evolution of amniote egg allowing exploitation of land320
Missipianshallow seas cover most of Earth360
Devonianvascular plants, the first tetrapods, wingless insects, arachnids, brachiopods, corals, and ammonite were also common, many new kinds of fish appeared408
SilurianCoral reefs, rapid spread of jawless fish, first freshwater fish, first fish with jaws, first good evidence of life on land, including relatives of spiders and centipedes438
Ordovicianmost dry land collected into Gondwana, many marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates), red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods, possibly first land plants505
Cambrianmost major groups of animals first appear, Cambrian explosion570
Proterozoicstable continents first appear, first abundant fossils of living organisms, mostly bacteria and archeobacteria, first eukaryotes, first evidence of oxygen build-up2500
Archeanatmosphere of methane, ammonia, rocks and continental plates began to form, oldest fossils consist of bacteria microfossils stromatolites, colonies of photosynthetic bacteria3800
Hadeanpre-geologic time, Earth in formation4500

Bibliography

Foster, Robert. Geology. 3rd ed. Columbus, OH: Charles E. Merrill, 1976.

Stanley, Stephen. Earth and Life Through Time. New York: W. H. Freeman, 1989.

Toulmin, Stephen and June Goodfield. The Discovery of Time. New York: Harper & Row, 1965.

Internet Resources

United States Geological Survey. <http://pubs.usgs.gov/gip/fossils/contents.html>.

geologic time-scale

views updated May 08 2018

geologic time-scale A two-fold scale that subdivides all the time since the Earth first came into being into named units of abstract time, and subdivides all the rocks formed since the Earth came into being, into the successions of rock formed during each particular interval of time. The branch of geology that deals with the age relations of rocks is known as chronostratigraphy. The concept of a geologic time-scale has been evolving for the last century and a half, commencing with a relative time-scale (mainly achieved through biostratigraphy), to which it has gradually become possible to assign dates (see DATING METHODS) which are, nonetheless, subject to constant revision and refinement. Since the first International Geological Congress in Paris in 1878, one of the main objectives of stratigraphers has been the production of a complete and globally accepted stratigraphic scale to provide a historical framework into which all rocks, anywhere in the world, can be fitted (see STANDARD STRATIGRAPHIC SCALE; CHRONOSTRATIGRAPHIC SCALE; UNIFIED STRATIGRAPHIC SCALE). Such a standard scale is still a long way off, but the names for geologic-time units and chronostratigraphic units down to the rank of period/system are in common use; many epoch/series and age/stage names are still regionally variable. See Time Scales gives an outline geologic time-scale employing currently common names and dates (though they are not necessarily universally accepted).

geologic time-scale

views updated May 29 2018

geologic time-scale A twofold scale that subdivides all the time since the Earth first came into being into named units of abstract time, and subdivides all the rocks formed since the Earth came into being into the successions of rock formed during each particular interval of time. The branch of geology that deals with the age relations of rocks is known as chronostratigraphy. The concept of a geologic time-scale has been evolving for the last century and a half, commencing with a relative time-scale (mainly achieved through biostratigraphy), to which it has gradually become possible to assign dates which are, nonetheless, subject to constant revision and refinement. Since the first International Geological Congress in Paris in 1878, one of the main objectives of stratigraphers has been the production of a complete and globally accepted stratigraphic scale to provide a historical framework into which all rocks, anywhere in the world, can be fitted. Such a standard scale is still a long way off, but the names for geologic-time units and chronostratigraphic units down to the rank of period/system are in common use; many epoch/series and age/stage names are still regionally variable.

geological time

views updated May 29 2018

geological time Time scale of the history of Earth. Until recently, only methods of relative dating were possible, by studying the correlation of rock formations and fossils. The largest divisions of geologic time are called eras, each of which is broken down into periods, which, in turn, are subdivided into series or epochs.

geological time scale

views updated May 18 2018

geological time scale A time scale that covers the earth's history from its origin, estimated to be about 4600 million years ago, to the present. The chronology is divided into a hierarchy of time intervals: eons, eras, periods, epochs, ages, and chrons.

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