"The Mediterranean Sea connects to the vastness of the Atlantic through the smallest of natural channels: The Strait of Gibraltar is only about 8 miles wide. People have swum across the Strait, and it is easy to see from Spain to Morocco on a normal, clear day. It seems like it would not take much for nature to simply close that connection between Europe and Africa, and in so doing isolate the Mediterranean Sea. Indeed, this has happened before."
"About six million years ago, something caused the Mediterranean to be cut off. Perhaps it was an ice age that decreased the sea level enough to leave a land bridge between Spain and Morocco. The Mediterranean's isolation could also have been the outcome of tectonic processes. In what is dubbed the Messinian salinity crisis, the Mediterranean Sea then evaporated over a period of about 1,000 years."
"There is interesting evidence to show how comprehensively the Mediterranean ran dry. Massive rivers like the Nile and the Rhône today empty into the Mediterranean at sea level. But during the period in question, these rivers reached the bed of the Mediterranean. In the process, they carved out great canyons that arrive at the seabed, 2,700 meters below sea level. At Cairo, the Nile's canyon was discovered during excavations for the Aswan Dam. Subsequent cores and surveys revealed a formation larger than the Grand Canyon."
The Strait of Gibraltar is about 8 miles wide, allowing visible sightlines between Spain and Morocco. Around six million years ago the Mediterranean became isolated, possibly from lowered sea level during an ice age or tectonic uplift. During the Messinian salinity crisis the sea evaporated over roughly 1,000 years, leaving a dry basin 3 to 5 km below sea level with saline lakes. Rivers such as the Nile and Rhône carved deep canyons down to about 2,700 meters below sea level. Marine cores reveal gypsum and rock-salt deposits up to 1 km thick. The basin refilled abruptly in a dramatic megaflood.
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