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( Paleocene)
The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65.5 ± 0.3 Ma to 55.8 ± 0.2 Ma (million years ago). It is the first epoch of the Palaeogene Period in the modern Cenozoic era. As with most other older geologic periods, the strata that define the epoch's beginning and end are well identified but the exact date of the end is uncertain. The Paleocene epoch immediately followed the mass extinction event at the end of the Cretaceous, known as the K-T boundary (Cretaceous - Tertiary), which marks the demise of the dinosaurs. The die-off of the dinosaurs left unfilled ecological niches worldwide, and the name "Paleocene" comes from Greek and refers to the "old(er)" (pa?a???, palaios) – "new" (?a????, kainos) fauna that arose during the epoch, before modern mammalian orders emerged in the Eocene. The K-T boundary that marks the separation between Cretaceous and Paleocene is visible in the geological record of much of the Earth by a discontinuity in the fossil fauna, with high iridium levels. There is also fossil evidence of abrupt changes in flora and fauna. There is some evidence that a substantial but very short-lived climatic change may have happened in the very early decades of the Paleocene. There are several theories about the cause of the K-T extinction event, with most evidence supporting the impact of a 10&_160;km diameter asteroid forming the buried Chicxulub Crater on the coast of Yucatan, Mexico. The end of the Paleocene (55.5/54.8&_160;Ma) was marked by one of the most significant periods of global change during the Cenozoic. The Paleocene-Eocene Thermal Maximum upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and a major turnover in mammals on land.
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