ENVR 201 Lecture Notes - Pleistocene, Ape, Pteridospermatophyta
16 Feb 2013
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Document Summary
In contrast to this largely unidirectional change in atmospheric o2 concentration, most physical conditions on earth have oscillated in response to the planet"s internal processes. For earth to be in a cold, dry state, atmospheric co2 levels had to have been unusually low. Extraterrestrial events have triggered changes on earth: a meteorite caused or contributed to a mass extinction at the end of the. Cretaceous period (65 mya): the first clue came from abnormally high concentrations of the element iridium in a thin layer separating rocks deposited during the. Cretaceous from those deposited during the tertiary: iridium is abundant in some meteorites; rare on earth"s surfaces. Life was confined to oceans and all organisms were small: over the precambrian the shallow seas slowly began to teem with life. The modern biota evolved during the cenozoic era: by early cenozoic ear (65 mya), the positions of the continents resembled those of today, cenozoic was characterized by extensive radiation of mammals.
