At the onset of the Paleocene Epoch, Earth was recovering from the end-Cretaceous asteroid impact. The climate was subtropical almost to the polar circles, ocean temperatures were high, and polar ice caps were absent. The Paleocene Epoch brackets two major events in Earth’s history. It started with the mass extinction event at the end of the Cretaceous, known as the Cretaceous–Paleogene boundary. This was a time marked by the demise of non-avian dinosaurs, giant marine reptiles, and much other fauna and flora.