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The Cenozoic The Cenozoic is Earth's current geologic era. It started approximately sixty-five million years before the present. The name means "recent life" and it is during this era that most mammalian species evolved. The Cenozoic is divided into two periods, the Tertiary and Quaternary. The boundary between the two periods was thought to mark the onset of glaciation, although it's now known that glaciation took place both before and after the start of the Quaternary. Scientists have divided the Tertiary Period into two main parts -- the Paleogene (ancient born) and Neogene (new born), based on a major change in fauna. You may be more familiar with a different way of dividing the Tertiary, into five epochs: the Paleocene, Eocene, Oligocene, Miocene and Pliocene. The Quarternary is divided into two epochs; the Pleistocene and Holocene. The start of the era is marked by a catastrophic event that caused global mass extinction. This event was partly the consequence of a meteorite crashing into Earth, in combination with massive volcanic eruptions. Although this brought about the extinction of the dinosaurs and many marine species, new species eventually evolved and repopulated the planet. It was around the start of the Cenozoic that the first primates and other mammals evolved, hence the era's nickname, the Age of Mammals. During the Cenozoic the breakup of the Pangea supercontinent was completed, bringing the continents into their present relative positions. Continental drift and plate tectonics influenced Earth's oceans, climate, and atmosphere, and affected the migration of animals and the spread of plants. By studying fossil plant and animal remains, researchers have an idea of what Earth looked like throughout the Cenozoic. Near the start of the era - that is, during the Paleocene and early Eocene -- mammalian life diversified into an amazing array of species. With the extinction of dinosaurs, mammalian species that had spent approximately 150 million years subordinate to the reptiles were exposed to new ecological opportunities, primarily in warm, subtropical conditions that emerged after the extinction event. Yet one of the most influential events occurred around the middle of the Eocene, when Earth underwent a dramatic climate change. During that time of global cooling, dense forests were replaced with open forests and grasslands and the polar icecaps began their formation. If you wish to learn more about the evolutionary history of the Cenozoic, look to the left where you will see the names of each epoch. Click on the name and you'll find a page that gives details about that epoch. This will help you put human evolution, which occurred near the end of the Cenozoic, into the framework of Earth's geologic time. Look at the Holocene to see the most recent epoch, which started about 11,000 years ago. |