A geological epoch lasting from about 56 to 34 million years ago, characterized by warm climates and the rise of early mammals.
From Greek eo- (early, dawn) plus kainos (new). Means 'early new' because it marked the early period of the modern mammalian fauna.
The Eocene is when the first horses, whales, and primates appeared—it's like watching the beginning of the modern world, with the ancestors of every mammal you know today showing up in the fossil record.
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