What Was the Earth Like During the Miocene Epoch?

The Miocene epoch encompasses the time between 23 and 5 million years ago on Earth. It means "less recent" in Greek, a reference to the fact that that the type and distribution of marine invertebrates during the period varied substantially from that of the most recent period, from 5 million years ago to the present. Otherwise, there are many similarities between the Miocene epoch and the present day (the Holocene). The Miocene epoch is the first epoch of the Neogene period, which began 23 million years ago and continues to the present. The Neogene period was preceded by the Paleogene.

The Miocene epoch marked the beginning of the world's great grasslands, which aggressively covered land left behind by dying forests. The first significant planetary event that occurred during the Miocene epoch was the separation of Antarctica from South America, creating the Drake Passage and enabling the frigid Antarctic Circumpolar Current. This caused Antarctica, which had been a temperate forest climate during the previous Paleogene period, to become covered in mile-thick glaciers. The climactic influence of Antarctica cooled down the entire planet to an extent.

Many modern mammalian groups were evolving significantly during the Miocene epoch, including felids, which emerged shortly before the start of the period, and modern-looking dogs, though canids had evolved over 16 million years before. Ursids (bears) and canids existed about 39 million years ago, but only in the early Miocene did they migrate from North America to Eurasia and Africa. Echolocation evolved during the Miocene, enabling whales and dolphins to observe their aquatic surroundings with a tool beyond sight. Primates began the epoch in a relatively primitive state. Apes diverged from Old World monkeys about 23 million years ago. By 18 million years ago they had evolved into great apes, and by 5 million years ago, intelligent precursors to the genus Homo existed. Australopithecus afarensis, one of the first major steps away from the great apes and towards humanity, didn't evolve until about 3.7 million years ago.

Broadleaf forests, which had previously existed up to 45 degrees away from the equator (including most of present-day Eurasia and the United States), receded back to only about 20 degrees from the equator during the Miocene epoch. This caused an evolutionary shift from arboreal species to grass-eating species. Many of the key mammals grew significantly in size, eventually giving rise to megafauna like elephants. In general, the Miocene can be thought of as the Age of Grasses, a circumstance which had never occurred before in the history of the Earth. Grasses evolved only about 80 million years ago and did not dominate the planet until the Miocene.