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The Mediterranean

The Mediterranean is a relic of the ancient Tethys Sea, which used to extend across much of Eurasia. It may still be closing up today. There are certainly some complicated tectonic processes going on in the region.

It’s a sea that’s permanently teetering on the edge, because the Sun evaporates off far more water then comes in from rivers. At the moment the shortfall is made up through the Straits of Gibraltar.

But just under 6 million years ago, the Straits got closed off, and the entire basin dried up in 2000 years. This picture comes from an Open University TV programme.

Four hundred thousand years later, the Straits opened up again, and the Mediterranean was reborn in a flood of biblical proportions.

Drilling operations in the floor of the basin have found salt deposits more than 2 km thick. The deposits have been dated to exactly this time. That’s a lot of salt, and to produce it, the entire sea must in fact have dried up and refilled again several times.

The water that evaporated fell to earth again as rain, where it eventually reached the oceans – as fresh water. It seems that there was enough of it to dilute the oceans and make them significantly less salty. This caused a minor (probably very minor) mass extinction. It also triggered an ice age, as the less salty Arctic and Antarctic oceans froze and reflected more sunlight back into space. The event is called the Messinian salinity crisis.

The crisis ended about 5.4 My. It’s not clear why it ended. The missing salt remains locked up beneath the Mediterranean to this day. So there must be some other explanation.