As hundreds of millions of tourists flock to the coasts of the Mediterranean Sea each year, it might be easy to overlook how this sea has played an integral part in human history.
The Levant, in the east, was one of the centres of agricultural development, and the world’s longest river (and the backbone of Ancient Egyptian civilisation) the Nile, empties into the sea. Later, the Roman Empire was partly able to retain its global imperial power through controlling Mediterranean waters.
But there’s a possibility that these events would never have occurred, as geologists have theorised that the Mediterranean was almost entirely dried up around 5.9 million years ago – with little water in sight.
Messinian salinity crisis
Instead of the Mediterranean Sea we see today, picture a vast expanse of salt flats spanning about 2,500,000 square kilometres (970,000 square miles).
During the Messinian age, it’s thought that the Mediterranean Sea was cut off from the Atlantic by the precursor of the Strait of Gibraltar. The sea gradually became extremely dry as part of an event now called the Messinian salinity crisis.
A few hypersaline lakes dotted the landscape, similar to the Dead Sea today. Only 11 per cent of endemic species survived the event, and it’s thought that it took at least another 1.7 million years for biodiversity to recover.
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Zanclean flood
In the 1970s, scientists drilled below the Mediterranean into rocks from the Messinian age. First, they discovered a layer of salt that descended kilometres below the seafloor. Above this layer was sediment containing fossils from low-salt, shallow lakes. The layer above this then abruptly shifted to sediment more typically found in deep-sea environments.
They concluded that a mass flooding event must have taken place to end the crisis and coined the term Zanclean Flood (as this marked the beginning of the Zanclean age).
But the rate of this flooding event has been contested by scientists ever since. Some hypothesise that the Mediterranean gradually refilled over a period of 10,000 years, while others believe that the resulting ‘Gibraltar Falls’ at the Malta Escarpment (dividing the east and west basins) would have thundered down from a point 1,000 times higher than Niagara Falls in a far shorter timescale.
If the timescale was relatively short, the weight of the rising water level would have triggered earthquakes that spread throughout the region.
New evidence
In 2009, scientists discovered an erosion channel that stretched from the Gulf of Cádiz (at the southernmost point of mainland Portugal) to the Alborán Sea (the westernmost point of the Mediterranean Sea).
They suggested that this pointed to a single, massive flooding event that lasted between two and 16 years.
The scientists estimated that the megaflood discharged through this channel at a rate of 68 to 100 Sverdrups (with one Sverdrup equal to one million cubic metres per second).
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And in 2025, researchers sampled ridges across the Sicily Sill: a submerged land bridge that once separated the western and eastern Mediterranean basins. They discovered that the ridges were topped with a layer of rock debris which contained material from the ridge flanks and surrounding region – suggesting that it was rapidly deposited with immense force.
The age of the layer can also be dated to the boundary of the Messinian and Zanclean ages. Using seismic reflection data, the researchers also found a W-shaped channel on the continental shelf east of the Sicily Sill. They have suggested that this acted as a massive funnel for the megaflood.
Computer modelling suggests that the megaflood would have grown in intensity as time went on, travelling at 115 kilometres per hour (71 miles per hour) and eroding more and more material as it went.
In the area that the team modelled, 13 million cubic metres of water per second would have flooded into the eastern Mediterranean basin. In comparison, the Amazon River (one of the fastest flowing rivers in the world) is around 200,000 cubic metres per second.
However, this is only a small fraction of the total amount of water that first flowed through Gibraltar and then later into the eastern Mediterranean.
“The Zanclean megaflood was an awe-inspiring natural phenomenon, with discharge rates and flow velocities dwarfing any other known floods in Earth’s history,” said Aaron Micallef, the lead author of the study and researcher at the Monterey Bay Aquarium Research Institute in California.
“Our research provides the most compelling evidence yet of this extraordinary event.”
As the Mediterranean Sea filled, marine animals such as great white sharks (as well as ancient cetaceans and dugongs) made their way into its waters.
Today, the Mediterranean Sea has the highest salinity level of all seas and oceans on Earth. It also presents a striking pattern in that the number of species found in the sea decreases from west to east.
Top image: view of the Atlantic Ocean, Strait of Gibraltar and Alborán Sea from the International Space Station. Credit: Stocktrek Images/Getty Images
