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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.
- Fall '10