The Paleocene Epoch is a time period in Earth’s history that lasted from approximately 65 million years ago to 56 million years ago. It is sometimes called the “old recent” period, as it followed the late-Cretaceous Period but precedes the Eocene Epoch. The Paleocene Epoch is the oldest time period of the Paleogene Period, which persisted until about 28 million years ago.
The beginning of the Paleocene Epoch occurred shortly after Earth was hit by an asteroid or meteor approximately 65 million years ago. This asteroid impact is thought to be at least partially responsible for the demise of the dinosaurs and the large marine reptiles of the time. Once the Paleocene Epoch began, Earth's climate became slightly cooler and less humid; however, at the beginning of the period, Earth’s climate was very warm. The polar ice caps did not exist during the beginning of the epoch, and subtropical temperatures nearly extended to the Arctic and Antarctic circles. Because little of the world’s water was frozen, the sea levels were higher and the coastal regions of many continents were covered by shallow seas.
Mammals began to replace most niches that were previously occupied by dinosaurs once the epoch began. At the end of the Paleocene, large quantities of methane were released, which caused the extinction of many deep-sea species.