Paleogene is a geologic period that spans 1 million years.
The Paleogene ( [ pronˈpæliːədʒiːn ] or [ ˈpeɪliːədʒiːn ] also spelled Palaeogene or Palæogene ; informally Lower Tertiary ) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya ) to the beginning of the Neogene Period Mya .