Geological Time Scale

views updated May 11 2018

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

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).

A Dictionary of Earth Sciences AILSA ALLABY and MICHAEL ALLABY

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.

A Dictionary of Ecology MICHAEL ALLABY

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.

World Encyclopedia

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.

A Dictionary of Biology