The Paleocene epoch was a geologic period lasting from about 66 to 56 million years ago, immediately following the Cretaceous-Paleogene (K-Pg) extinction event that wiped out the non-avian dinosaurs. It's the first epoch of the Paleogene Period. It is characterized by a warming climate and the diversification of mammals as they filled the ecological niches left vacant by the extinct dinosaurs.
The most widely accepted theory for the extinction of the dinosaurs is that the impact of a large asteroid or comet roughly 10 kilometers (6 miles) in diameter is generally considered significant enough to cause a mass extinction event on Earth. Such an impact could trigger global environmental catastrophes, potentially leading to widespread loss of life and drastic changes in the biosphere. This event, known as the Cretaceous-Paleogene (K-Pg) extinction event, triggered a cascade of environmental changes that led to widespread extinction, including the dinosaurs approximately 66 million years ago.