Interval of geologic time, 65–1.
8 million years ago. It constitutes the first of the two periods of the Cenozoic Era , the second being the Quaternary . The Tertiary has five subdivisions: (from oldest to youngest) the Paleocene , Eocene , Oligocene , Miocene , and Pliocene epochs. During most of the Tertiary, the spatial distribution of the major continents was largely similar to that of today. Emergence and submergence of land bridges between continents critically affected the distribution of both terrestrial and marine animals and plants. Virtually all the existing major mountain ranges were formed either partly or wholly during the Tertiary.