The geological evolution of the Black Sea (1)
	Some 50-60 million years ago, before the beginning of the Tertiary Period, a vast oceanic basin extended from west to east across Southern Europe and Central Asia, linking the Atlantic Ocean and the Pacific Ocean. It was the salty Tethys Sea. By the middle of the Tertiary Period, as a result of crust upheavals, the Tethys Sea had become separated first from the Pacific Ocean and later from the Atlantic.
	Major crust movements led to mountain-building in the Miocene (from 5 to 7 million years ago) and the formation of the Alps, the Carpathians, the Balkan Mountains and the Caucasus Mountains. As a result the Tethys Sea shrunk in size and became divided into a number of brackish basins. One of them, the Sarmatic Sea, stretched from the present location of Vienna to the foothills of the Tien Shan Mountains and included the modern Black Sea, the Azov Sea, the Caspian Sea and the Aral Sea. The Sarmatic Sea was separated from the ocean, and gradually its salinity fell as a result of the inflow from rivers. It is assumed that the salinity in the sea was even lower than in the modern Caspian Sea. Much of the marine fauna endemic to the Tethys Sea became extinct. However, it is interesting to note that typically oceanic animals, such as whales, manatees and seals, continued to inhabit the Sarmatic Sea for a long time, before they too disappeared.
	By the late Miocene and early Pliocene (3-5 million years ago) the Sarmatic Sea had shrunk to the size of the Maeotic Sea. During that period a link to the ocean was again established, salinity increased and marine species of plants and animals settled in the sea. In the Pliocene (1.5 - 3 million years ago) the connection to the ocean was again severed, and the salty Maeotic Sea was replaced by the almost freshwater Pontian Sea-Lake. Within it the future Black and Caspian Seas were connected through the present-day northern Caucasus. Marine fauna disappeared from the Pontian Sea-Lake and were replaced by brackish-water fauna. To this day its representatives can still be found in the Caspian Sea, the Azov Sea and the regions of the Black Sea with reduced salinities. These species are today referred to Pontian relics or Caspian fauna, since they have been best preserved in the reduced salinities of the Caspian Sea. In the late Pontian stage the Earth's crust began to rise in the northern Caucasus, gradually isolating the Caspian Sea from the basin. From that period onwards the Caspian Sea, on the one hand, and the Black Sea and the Azov Sea, on the other, went their separate ways, although temporary links between them were formed from time to time.
	With the onset of the Quaternary Period and the Ice Age the salinity and species composition of the developing Black Sea continued to change, as did the outline of the sea. By the late Pliocene (less than one million years ago) the Pontian Sea-Lake had shrunk to the size of the Chaudian Sea-Lake. It had a reduced salinity, was isolated from the ocean and inhabited by fauna of the Pontian type. Evidently, the Azov Sea had not yet come into existence.
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