The first period of the * Cenozoic era from about 65 to 2 million years ago. It began with the Palaeocene epoch, which was followed by the Eocene, Oligocene, Miocene, and Pliocene (Pleiocene) epochs. The climate was tropical to the end of the Oligocene, becoming cooler and drier towards the end of the period as the oceans contracted and the present mountain ranges were formed. Abundant plant fossils have been found, many showing similarity to modern-day plants. Changes in the distribution of the flora can be related to changes in climate throughout the era. Siliceous remains of diatoms, the diatomaceous earths (Kieselguhr) are widespread, blue-green algae contributed to the formation of oil shales, green and red algae contributed to marine limestone deposits, and the fossil stoneworts contributed to the formation of freshwater limestone beds. The Gnetales appeared and modern genera of the Coniferales are represented. By the end of the period, the angiosperms were firmly established with about 260 families. This was accompanied by the evolution of insects. Grasses became more abundant in the Miocene, possibly because of the change to a drier climate. See geological time scale. |
