The Paleocene was the ten million years when mammals inherited an emptied planet
An asteroid ended the age of dinosaurs about 66 million years ago, and a vast burst of carbon closed the next chapter ten million years later. Between those two catastrophes lay the Paleocene, a hot, ice-free world of dense forests, even at the poles, where small, fast-evolving mammals spread into the gaps.
The epoch opened with the K–Pg extinction. A space rock 10 to 15 kilometres wide gouged out the Chicxulub crater in the Yucatán, and together with eruptions of the Deccan Traps it wiped out about three quarters of all species. Around the world the boundary shows up as a thin band rich in iridium, with sudden breaks in the fossil plants and animals above and below it. Species that had been rare took over from those that had dominated.
The recovering world was warm, averaging around 24 to 25 °C against roughly 14 °C recently, with no permanent polar ice. Forests covered much of the land and grew thick in the near absence of large plant-eaters, though they held relatively few plant species. The first placental and marsupial mammals appear in rocks of this age, and in the oceans ray-finned fish came to rule open water and rebuilding reefs. The map looked unfamiliar: the Americas were still separate, the Rockies were rising, India had begun pushing into Asia, and ocean currents sank in the North Pacific rather than the North Atlantic.
The ending was just as dramatic. During the Paleocene–Eocene Thermal Maximum, around 55.8 million years ago, between 2,500 and 4,500 gigatons of carbon poured into the air and sea, sending temperatures soaring and acidifying the oceans. Somewhere between 30 and 50 percent of seafloor foraminifera, tiny shelled organisms used to gauge marine health, disappeared.
The geologist Wilhelm Philipp Schimper coined the name in 1874 while describing rocks near Paris. It combines Greek words for old and new and means the old part of the Eocene, though it saw little use until about 1920. Geologists split the epoch into three ages, the Danian, Selandian and Thanetian.
Source: Paleocene
