The Mediterranean, Black Sea and Caspian are leftovers of one vanished ocean
Long before the Alps and Himalayas rose, an ocean called the Tethys lay between the great southern and northern landmasses. As Africa, India and Arabia drifted north and slammed into Eurasia, it was squeezed into fragments. Its remnants include today's Indian Ocean, the Mediterranean, and the landlocked Black and Caspian seas.
Geologists recognise a whole succession of Tethys oceans. A Paleo-Tethys existed from the Cambrian into the Early Triassic. Around 250 million years ago a sliver of continental shelf called Cimmeria split from the southern supercontinent Gondwana and crept north over some 60 million years, shoving the old seafloor beneath northern Pangaea. The new, or Neo-Tethys, ocean opened behind it. When Cimmeria finally jammed against Laurasia about 150 million years ago, sea levels rose and shallow Tethys waters spread over much of Europe.
At its widest, the Tethys formed part of a continuous seaway circling the planet between roughly 30 degrees north and the Equator, so ocean currents behaved very differently from today. Its Late Cretaceous waters swarmed with marine reptiles and cephalopods, and on its European islands evolution took odd turns: dinosaurs such as Telmatosaurus shrank through island dwarfism, while the pterosaur Hatzegopteryx grew into a giant apex predator. Several big mosasaurs competed in the same seas.
The end came in stages. As Africa and Arabia pushed north and the growth of Antarctic ice lowered sea levels, the link between the Atlantic and Indian oceans across what is now the Middle East closed, in two steps around 20 and 14 million years ago. The rerouting of currents is thought to have allowed upwelling in the Arabian Sea and set up the modern South Asian monsoon. The collisions also raised the Alpide mountain belt, from the Alps to the Zagros, Caucasus and Himalayas.
A northern arm, the Paratethys, was cut off about 34 million years ago and covered much of central and eastern Europe until it largely dried out roughly 5 million years ago; the Black and Caspian seas are its survivors. In 1845 Roderick Murchison inferred a vast brackish sea larger than the Mediterranean from fossils spread from the Black Sea to the Aral. In 1885 Melchior Neumayr deduced the ocean itself, and it takes its name from a Greek sea goddess.
Source: Tethys Ocean
