Geologic time scale

Geologic time scale - proposed by the International...

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Geologic time scale This clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga. [1] Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale. The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists , paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth . The table of geologic time spans presented here agrees with the dates and nomenclature
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Unformatted text preview: proposed by the International Commission on Stratigraphy , and uses the standard color codes of the United States Geological Survey . Evidence from radiometric dating indicates that the Earth is about 4.570 billion years old . The geological or deep time of Earth's past has been organized into various units according to events which took place in each period. Different spans of time on the time scale are usually delimited by major geological or paleontological events, such as mass extinctions . For example, the boundary between the Cretaceous period and the Paleogene period is defined by the CretaceousTertiary extinction event , which marked the demise of the dinosaurs and of many marine species. Older periods which predate the reliable fossil record are defined by absolute age. Each era on the scale is separated from the next by a major event or change....
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This note was uploaded on 12/21/2011 for the course AMH AMH2010 taught by Professor Pietrzak during the Fall '10 term at Broward College.

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Geologic time scale - proposed by the International...

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