The Mediterranean Sea nearly underwent a near-total evaporation process.
In an era spanning over five million years ago, the Mediterranean Sea experienced a dramatic transformation. The water in the sea became increasingly salty, leading to the death of countless plant and animal species. Only around eleven percent of the species native to the area managed to survive this salt crisis, as reported by a research team in the journal "Science". It took an impressive 1.7 million years for biodiversity to return after fresh water began flowing back into the basin once again.
Today, the only passage between the Atlantic and the Mediterranean is the Strait of Gibraltar, a narrow channel that allows fresh water to flow into the saltier Mediterranean. According to current theories, this passage closed around 6 million years ago as a result of Earth's upper mantle shifting. This shift caused significant changes in salinity and temperature in the Mediterranean around 7.6 million years ago.
A Sea's Desolation
Without the influx of water from the Atlantic, the Mediterranean eventually dried up, with the inflow from rivers like the Nile and the Ebro unable to maintain the water level. This led to the accumulation of a kilometer-thick salt layer beneath the sea, as reported by a team led by Konstantina Agiadi from the University of Vienna.
To explore the impact of these extreme changes on Mediterranean life, the researchers analyzed fossils from coastal countries and deep-sea sediment cores that were 12 to 3.6 million years old.
A Breeding Ground for Extinction
Following the Messinian Salinity Crisis, as reported in the study, two-thirds of the species in the Mediterranean were wiped out. Coral reefs in tropical regions perished, and only 86 of the original 779 Mediterranean-specific species survived. The researchers are still unsure of how these surviving species managed to do so.
As soon as the Atlantic flowed back into the basin around 5.33 million years ago, previously non-native species reclaimed their habitats. White sharks and dolphins also began inhabiting the Mediterranean.
Surprisingly, the recovery of the ecosystem took an unusually long time, as the team led by Agiadi reported. The current pattern of decreasing biodiversity from west to east still exists in the Mediterranean. The Mediterranean's biodiversity is unusually high for its size due to the many species unique to the region.
A Hostile Salt Desert
Paleontologist and evolutionary biologist Thomas Halliday describes the situation in his book "Urwelten". As the water receded, the Mediterranean region formed islands that became mountains. Valleys up to four kilometers beneath sea level were created, and the maximum air temperature in these valleys on a hot summer day could reach as high as 80 degrees Celsius - 25 degrees higher than the hottest temperature ever recorded in modern-day Death Valley.
At the bottom of the Mediterranean basin, layers of gleaming gypsum and sodium chloride up to three kilometers thick formed in some areas. The water from the Atlantic eventually flowed back into the western basin, and later the eastern basin was filled - potentially through the "most powerful waterfall the Earth has ever seen".
A Waterfall of Superlatives?
It's estimated that this waterfall was 1500 meters tall, with water rushing over the cliff at speeds of nearly 250 km/h and turning into mist before reaching the bottom. Despite this constant deluge that raised the eastern Mediterranean by one meter every two and a half hours, it took over a year for the eastern Mediterranean to be filled, separating Malta, Gozo, Sicily from Africa, and Italy, and turning Gargano into an island once again.
Salt Deposits
Throughout Earth's history, movements in the Earth's crust have resulted in the isolation of various marine areas from oceans and the formation of massive salt deposits, as reported by the researchers led by Agiadi. These salt giants, consisting of thousands of cubic kilometers, have been found in various locations, including Australia, Siberia, the Middle East, and elsewhere. Salt extraction has been conducted in these areas since ancient times, such as in the Hallstatt mine in Austria and the Khewra salt mine in Pakistan.
The scientific investigation of the Messinian Salinity Crisis led to the discovery of a kilometer-thick salt layer beneath the Mediterranean Sea. The study, published in various academic journals, reported the extinction of two-thirds of the Mediterranean's species following the crisis.
