geologic timescale

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Geological Time Scale

Geologic Time Scale
Era Period Epoch Significant Events Million Years Before Present
Cenozoic Quartenary Holocene recorded human history, rise and fall of civilizations, global warming, habitat destruction, pollution mass extinction 0.01
Pleistocene Homo sapiens, ice ages 1.6
Tertiary Pliocene global cooling, savannahs, grazing mammals 5.3
Miocene global warming, grasslands, Chalicotherium 24
Oligocene 37
Eocene modern mammals flourish, ungulates 58
Paleocene 66
Mesozoic Cretaceous last of age of dinosaurs, modern mammals appear, flowering plants, insects 144
Jurassic huge plant-eating dinosaurs, carnivorous dinosaurs, first birds, breakup of Pangea 208
Triassic lycophytes, glossopterids, and dicynodonts, and the dinosaurs 245
Paleozoic Permian Permian ends with largest mass extinction in history of Earth, most marine inverterbrates extinct 286
Pennsylvanian vast coal swamps, evolution of amniote egg allowing exploitation of land 320
Missipian shallow seas cover most of Earth 360
Devonian vascular plants, the first tetrapods, wingless insects, arachnids, brachiopods, corals, and ammonite were also common, many new kinds of fish appeared 408
Silurian Coral 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 centipedes 438
Ordovician most 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 plants 505
Cambrian most major groups of animals first appear, Cambrian explosion 570
Proterozoic stable continents first appear, first abundant fossils of living organisms, mostly bacteria and archeobacteria, first eukaryotes, first evidence of oxygen build-up 2500
Archean atmosphere of methane, ammonia, rocks and continental plates began to form, oldest fossils consist of bacteria microfossils stromatolites, colonies of photosynthetic bacteria 3800
Hadean pre-geologic time, Earth in formation 4500

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>.

Animal Sciences
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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).

A Dictionary of Earth Sciences AILSA ALLABY and MICHAEL ALLABY
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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.

A Dictionary of Ecology MICHAEL ALLABY
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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.

World Encyclopedia
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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.

A Dictionary of Biology