The Cainozoic (Cenozoic) is the current geological era. It began 66 million years ago and continues today. Before it was the Mesozoic.
During the Cainozoic the continents moved into their present positions. The climate started warm, but cooling continued steadily. Finally ice ages occurred.
The word Cainozoic is derived from Greek kainos = "new", and zoe = "life". 'Cainozoic' may be spelled 'Cenozoic'. It has three periods, and the periods are split into stages.
Previously, what is now the Cainozoic was divided into two periods, the Tertiary and the Quaternary. The Tertiary corresponded to the Palaeogene+Neogene. Now, the term 'Tertiary' is not used. Officially, it is 'deprecated'.