Cretaceous Extinction

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The Cenozoic era-coming just after the Cretaceous Extinction, and extending as it does to the latest tick of time-was subdivided in the eighteen-thirties according to percentages of molluscan species that have survived into the present. From the Eocene, for example, which ended some thirty-five million years ago, roughly three and a half per cent have survived. Eocene means “dawn of the recent.” The first horse appeared in the Eocene. Looking something like a toy collie, it stood three hands high. From the Miocene (“moderately recent”), some fifteen per cent of molluscan species survive; from the Pliocene (“more recent”), the number approaches half. As creatures go, mollusks have been zakelijke energie particularly hardy. Many species of mammals fell in the Pliocene as prairie grassland turned to tundra and ice advanced from the north. From the Pleistocene (“most recent”), more than ninety per cent of molluscan species live on. The Pleistocene has also been traditionally defined by four great glacial pulsations, spread across a million years-the Nebraskan ice sheet, the Kansan ice sheet, the Illinoian and Wisconsinan ice sheets. It now appears that these were the last of many glacial pulsations that have occurred in relatively recent epochs, beginning probably in the Miocene and reaching a climax in the ice sheets of Pleistocene time. The names of the Cenozoic epochs were proposed by Charles Lyell, whose Principles of Geology was the standard text through much of the nineteenth century. To settle problems here and there, the Oligocene (“but a little recent”) was inserted in the list, and the Paleocene (“old recent”) was zakelijke energie vergelijken sliced off the beginning. Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene-sixty-five million to ten thousand years before the present. Divisions grew shorter in the Cenozoic-the epochs range from twenty-one million years to less than two million-because so much remains on earth of Cenozoic worlds.