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The Earth is thought by geologists to be 4.6 billion years old. The geologic or "deep" time of Earth's past has been organized into various periods according to events which took place in each period.
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| Years Ago3,6 | Epoch | Period/Age4,5 | Era | Eon | Major Events | |
|---|---|---|---|---|---|---|
| Present day | Holocene | Quaternary | Cenozoic | Phanerozoic | End of ice age and rise of modern civilizationFor alternative meanings see Civilization (disambiguation Teotihuacan, Mexico. Building projects of this size require the social organization found in civilizations. A civilization or civilisation has a variety of meanings related to human society. The te | |
| 11430 | PleistoceneThe Pleistocene epoch is part of the geologic timescale, usually dated as 1. 6 million to 10,000 years before present, with the end date expressed in radiocarbon years. It covers most of the latest period of repeated glaciation, up to and including the Yo | Extinction of many large mammalSubclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorps. Evolution of fully modern humanHuman beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. Biologically, they are classified as Homo sapiens ( Latin for knowing man , a primate species of mammal with a highly developed brain. In spirituas | ||||
| 1.81 million | PlioceneThe Pliocene epoch is the period in the geologic timescale that extends from about 5 million to 1. 6 million years before present. The Pliocene follows the Miocene epoch and is followed by the Pleistocene epoch. The Pliocene is the fifth and last epoch of | TertiaryThe Tertiary period is one of the major divisions of the geologic timescale, from the end of the Cretaceous period about 64 million years ago to the start of the Quaternary period about 1. 6 million years ago. The Tertiary includes five geologic epochs th | NeogeneNeogene Period A unit of geologic time consisting of the Miocene and Pliocene Epochs. The Neogene Period follows the Paleogene Period and is followed by the Quaternary Era. The terms 'Neogene System' and 'Upper Tertiary System' have also been used to desc | |||
| 5.33 million | MioceneThe Miocene Epoch is a period of time that extends from about 5 million to 24 million years before the present. As with other older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the start and end | |||||
| 23.0 million | Oligocene | Paleogene | ||||
| 37.2 million | Eocene | Appearance of first "modern" mammals | ||||
| 55.8 million | Paleocene | |||||
| 65.5 million* | Cretaceous | Mesozoic | Dinosaurs reach peak, become extinct. Primitive placental mammals | |||
| 146 million | Jurassic | Marsupial mammals, first birds, first flowering plants | ||||
| 200 million | Triassic | First dinosaurs, Egg-laying mammals, breakup of Pangea into Gondwana and Laurasia | ||||
| 251 million* | Permian | Paleozoic | Permian extinction event- 95% of life on Earth becomes extinct | |||
| 299 million | Carboniferous1 | Pennsylvanian | Abundant insects, first reptiles, coal forests | |||
| 318 million | Mississippian | Large primitive trees, first land vertebrates | ||||
| 359 million | Devonian | First amphibians, clubmosses and horsetails appear, progymnosperms (first seed bearing plants) appear | ||||
| 416 million* | Silurian | First vascular land plants, first jawed fish | ||||
| 443 million* | Ordovician | Invertebrates dominant; first land plants | ||||
| 488 million* | Cambrian | Major diversification of life in the Cambrian explosion | ||||
| 542 million* | Ediacaran | Neoproterozoic | Proterozoic2 | First multi-celled animals | ||
| 630 million*,8 | Cryogenian | Possible snowball Earth period, Rodinia begins to break up | ||||
| 850 million | Tonian | First acritarch radiation | ||||
| 1.0 billion | Stennian | Mesoproterozoic | Formation of Rodinia | |||
| 1.2×109 | Ectasian | |||||
| 1.4×109 | Calymmian | |||||
| 1.6×109 | Statherian | Paleoproterozoic | First complex single-celled life | |||
| 1.8×109 | Orosirian | Transition to oxygen atmosphere | ||||
| 2.05×109 | Rhyacian | |||||
| 2.3×109 | Siderian | |||||
| 2.5×109 | Neoarchean | Archaean2 | ||||
| 2.8×109 | Mesoarchean | |||||
| 3.2×109 | Paleoarchean | |||||
| 3.6×109 | Eoarchean | Simple single-celled life | ||||
| 3.8×109 | Hadean2,7 | 4.1×109 - Oldest known rock; 4.4×109 - Oldest known mineral; 4.57×109 - Formation of Earth | ||||
1) In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods.
2) The Proterozoic, Archean and Hadean are often collectively referred to as Precambrian Time, and sometimes also as the Cryptozoic.
3) Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where we would most like to have them. Dates with an * are radiometrically determined based on internationally agreed to GSSPs. The dates quoted above are according to the International Commission on Stratigraphy 2004 time scale. All dates given are for the end of the interval in question.
4) Paleontologists often refer to faunal stages rather than geologic Periods. The Stage Nomenclature is quite complex. See Harland for an excellent time ordered list of faunal stages. Also see the article on GSSPs.
5) In common usage the Tertiary- Quaternary and Paleogene- Neogene- Quaternary Periods are treated as equivalents to the Mesozoic and Paleozoic Periods. The term 'Period|Age' (e.g. ' Neogene Period|Age') is sometimes used instead of 'Period'.
6) The time shown in the "Years Ago" column is that of the end of the interval named beside it.
7) Hadean was sometimes called Priscoan.
8) The GSSP for the base of the Ediacaran, ratified in 2004, is a climatic/geochemical marker rather than biostratigraphic. It represents the end of a widespread glaciation event.
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