Eocene
Americanadjective
noun
adjective
noun
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The second epoch of the Tertiary Period, from about 58 to 37 million years ago. During the earliest part of this epoch, land connections existed between Antarctica and Australia, between Europe and North America, and between North America and Asia, and the climate was warm. The land connection between Antarctica and Australia disappeared in the mid-Eocene and early Oligocene, resulting in a change in the predominant oceanic currents and a cooler climate. With this change, the average size of mammals changed from less than 10 kg (22 lbs) to more than 10 kg. The Himalayas also formed during the Eocene, and most modern orders of mammals appeared.
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See Chart at geologic time
Other Word Forms
Etymology
Origin of Eocene
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
From there, these snakes could have spread through southern Europe and into Africa during the Eocene, a period spanning roughly 56 to 34 million years ago.
From Science Daily ● Apr. 29, 2026
Dr. Marc Jones, a curator of fossil reptiles and amphibians who co authored the research, notes that the Eocene was marked by major climate shifts worldwide.
From Science Daily ● Dec. 31, 2025
By contrast, the earlier Eocene, when C02 reached 1000 ppm and the global mean temperatures were 13º C warmer than today, could represent the worst case scenario.
From Salon ● Feb. 17, 2025
Indeed, from the larger perspective of Earth’s planetary history, Antarctica was green for a large chunk of time, specifically during the period prior to the Eocene Epoch 56 million years ago.
From Salon ● Oct. 19, 2024
Archie wanted to discuss the Eocene skull he was holding, but all the others could talk about was the game.
From "Stargirl" by Jerry Spinelli
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