c. 6.5 Million BCE

The Mediterranean Sea

The collision of the African and Eurasian continental plates, which started some 70–60 million years ago, closed off a great ocean basin that had existed between the continents. That basin, filled by the now-gone Tethys Sea, was part of an oceanic plate that was subducted and melted underneath the colliding African and Eurasian plates. The collision led to significant regional volcanism, as well as a zone of mountain-building across northern Africa and southern Europe.

The collision of Africa and Eurasia appears to have cut the remains of the Tethys Sea off from the rest of the Atlantic Ocean around 6 million years ago, beginning an era of many hundreds of thousands of years of drying out. Evaporation of the landlocked seawater resulted in the formation of thick, extensive layers of salt over much of the original and newly formed parts of the Tethys basin. In some places, the salt deposits are more than 1.9 miles (3 kilometers) thick. This “salinity crisis” in the basin between Africa and Eurasia nearly dried up the former Mediterranean Sea over the course of more than 600,000 years.

The crisis ended rather suddenly, however, about 5.3 million years ago when the natural dam between the Atlantic Ocean and the Mediterranean basin was catastrophically breached at the current Strait of Gibraltar. Ocean waters rushed back into the basin at a rate estimated to have been about 1,000 times the discharge rate of the Amazon River today, refilling parts of the basin by up to 30 feet (10 meters) per day. After only a few months of this deluge, much of the modern Mediterranean Sea had been refilled.

What had been the humid, subtropical climate conditions of that region of the world changed starting a few million years ago, when fossil evidence records a shift to the drier “Mediterranean climate” conditions of today. The region became heavily wooded with coniferous trees (such as the cedar on the flag of Lebanon) and other plants that could handle the hot and dry summer conditions. Since then, the ecology of the Mediterranean region has been dramatically altered, however, by thousands of years of human influence.

SEE ALSO Continental Crust (c. 4 Billion BCE), Plate Tectonics (c. 4–3 Billion BCE?), Roots of the Pyrénées (c. 500 Million BCE), Pangea (c. 300 Million BCE), The Atlas Mountains (c. 300 Million BCE), The Atlantic Ocean (c. 140 Million BCE), The Alps (c. 65 Million BCE), Sahara Desert (c. 7 Million BCE), The Caspian and Black Seas (c. 5.5 Million BCE)

Artistic rendering, based on geophysical data, of the Mediterranean basin just before the collision between Africa and Southern Europe cut it off from the Atlantic Ocean.