According to some chronologies of Old Earth, the first period of the Cenozoic Era, sometimes called the age of mammals, lasting from 65 to 2.6 million years ago. It was preceded by the last epoch of the Cretaceous, and followed by the Quaternary period. This usage fell out of fashion in the Information Age and the epochs within the Quaternary were reassigned to the Paleogene and Neogene, but scholars in some times and places since have preferred the older usage.
The Tertiary saw the rise of the mammals and birds as dominant large life forms on land. From an initially mild, wet, and tropical condition, the planet's overall climate grew progressively cooler and drier, and the seasons grew more pronounced.
Elsewhere in the regions of the galaxy that are now within the Terragen Sphere a number of sophont species developed significant interplanetary or even interstellar civilizations. These included the Muuh, the Soft ones, the Tunnlers, the Iahi Daohn, the originators of the Cybyota, the builders of the Black Acropolis, the Doreens, the Thyresta, and the Auld Limners. Most are now extinct, a few remain as low technology civilizations, and the Muuh and Soft Ones are greatly reduced in extent. In most of these cases the causes of these changes are not well understood (see Fermi Paradox). None of these civilizations is known to have influenced the course of life on Old Earth.
K-T Extinction - Text by M. Alan Kazlev Terragen mass extinction that occurred 65 million years ago, at the boundary of the Cretaceous and Tertiary periods. Caused by an asteroid or comet impact on the Yucatan Peninsula, resulting in prolonged darkness and rapid global temperature change. It resulted in the extinction of a number of important groups of animal life, including dinosaurs, plesiosaurs, mosasaurs, pterosaurs, ammonites, and several groups of plankton. Plants, small invertebrates, small reptiles and amphibians, small birds, and nocturnal mammals were not unduly affected, and large scavenging reptiles (crocodiles) also were able to survive. The K-T extinction event was a Level IV Mass Extinction.
Quaternary Period - Text by Stephen Inniss On Old Earth the third period (or second according to some) of the Cenozoic Era on Old Earth beginning 2.8 million years ago. It follows the Neogene (or according to some divisions the Tertiary) period, and consists of the Pleistocene, Holocene, and Gaiacene epochs.