The Tethys is composed of several smaller regions. The western region, often simply referred to as the Tethys Sea or the Western Tethys Ocean, was positioned between the continents of Laurasia and Gondwana during the Mesozoic. The Black, Caspian, and Aral Seas are thought to be its modern remains. Likewise, the eastern region is sometimes referred to as the Eastern Tethys Ocean.
During the Oligocene, large parts of Europe were covered by a northern branch of the Tethys called the Paratethys. It was eventually separated from the main Tethys by the formation of the Alps, and became an isolated inland sea before finally disappearing.
The "Tethys" name has been adopted to name oceans that appeared earlier in Earth's history. For example, the Paleo-Tethys Ocean existed during the Paleozoic.
During the Triassic, approximately 250 million years ago, a new ocean began to form in the southern end of the Paleo-Tethys Ocean. The Cimmerian tectonic plate formed along southern Pangaea and moved northwards, colliding with Laurasia in the Jurassic and creating a large ocean trench. Meanwhile, Laurasia and Gondwana began separating, opening up an ocean channel between the two continents.
As the landmasses continued to break up, the Tethys eventually became surrounded on all sides, and as sea levels fell during the Cenozoic, it eventually disappeared.
In 1893, Austrian geologist Eduard Suess proposed that an inland sea had once existed between Laurasia and Gondwana based on fossil evidence. He named it the Tethys Sea after the Greek goddess Tethys. In the 1960s, with the arrival of the theory of plate tectonics, it became clear that Suess's "sea" was in fact an ocean.