The Mediterranean Sea may have been partially or entirely dry during the Miocene, about 3 million years ago, due to the “Messinian salinity crisis”. The Strait of Gibraltar has closed at least several times over a period of 700,000 years, causing the water to evaporate repeatedly. The dry basin would have been a lifeless and hot place due to high salinity and geographic areas up to 3 miles (4.8 kilometers) below sea level.
It appears that, at some point in the recent geological past, the Mediterranean Sea may have been at least partially dry. A study conducted in the 1960s found a layer of minerals in the seabed that could only have been created by water evaporation.
In 1961, seismic surveys were carried out on the Mediterranean basin which found a geological feature 330 to 660 feet (100 to 200 meters) below the bottom of the Mediterranean sea, dubbed the M reflector. In 1968, the Deep Sea Drilling Project (DSDP) began ), supported by Texas A&M University, and while lifting rock cores from the seabed, the Glomar research vessel Challenger discovered a layer of evaporites up to 1.86 kilometers thick. These minerals, including anhydrite, gypsum, rock salt and arroyo gravel, are evidence that the water body was partially or entirely evaporated in the recent geological past, during the Miocene, about 3 million years ago. This event was later called the “Messinian salinity crisis”, from the name of the Messinian evaporite discovered on the island of Sicily.
Scientists later pieced together the evidence and determined what was happening in the Mediterranean Sea at the time. The Strait of Gibraltar has closed at least several times over a period of 700,000 years. The evaporite layer was too thick to be deposited in a single event, suggesting that water in the Mediterranean evaporated repeatedly. Even today, water evaporates faster than it is replenished, due to the lack of large ice mountains as a source of water and its relative disconnection from the world’s oceans. If these waterways were closed, the sea would evaporate dry in just a thousand years.
Although some parts of the Mediterranean are up to 3 miles (4.8 kilometers) deep, comparable to the depths of the ocean, the depth of the Strait of Gibraltar is around 1,000 feet (300 meters), still very deep, but possibly variable. About 5.9 million years ago, the Eurasian and African tectonic plates would have been closer together and the strait was probably shallower. When the water froze in the glaciers, it may have been taken from the world’s oceans and lowered sea levels enough to close the strait. More profound changes to the underlying crust caused by tectonic forces may have been at play, for example by changing the overall density of rocks.
The dry basin of the Mediterranean would have been a lifeless and hot place due to high salinity and geographic areas up to 3 miles (4.8 kilometers) below sea level. By comparison, the lowest point on earth today, the shore of the Dead Sea, is just 1,371 feet (418 meters) below sea level. At Mediterranean level there would be 1.7 times the atmospheric pressure at sea level. That means a wind blowing there would be 57°F to 85°F (32°C to 47°C) hotter there than sea level, which may have been scorching. The evaporites covering the entire basin would preclude any plant or animal life, so the area would have been one of the harshest deserts on Earth.
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