In-depth research has shed new light on the astonishing and awe-inspiring history of the Paratethys Sea. This 12-milion-year-old megalake was formed in Eurasia by the same tectonic shifts that created many European and Asian mountain ranges. It was the Earth’s largest lake, covering more area than the modern-day Mediterranean Sea .
Until now, not much was known about the lake’s geological history, or about its relationship to the surrounding environment. But two new studies have revealed some fascinating information about how the Paratethys Sea was created, how it disappeared, and how its fluctuations in size and shape ultimately influenced the evolution of modern animal species.
Chart showing the comparison between the water volume of the Paratethys Sea and that of other water bodies. Utrecht University )
The Rise and Fall of the Earth’s Largest Lake
Under the leadership of paleo-oceanographer Dan Palcu from the University of São Paulo in Brazil, an international team of geologists, geographers, and evolutionary biologists performed a detailed analysis of fossils and geological samples taken from the area that was once covered by the Paratethys Sea. They recently disclosed their mind-blowing discoveries in the journal Scientific Reports , and it seems their work has solved many of the mysteries involving the life and death of this massive inland body of water.
At its peak size, the Paratethys Sea covered an area of approximately 1.7 million square miles (2.8 million square kilometers), the researchers report. It bisected the Eurasian continental mass, flooding the lands of what is now Central Europe and creating a watery border that separated northern from southern Asia. Before climate change caused it to shrink, the Paratethys Sea extended from the eastern Alps to what is now the nation of Kazakhstan.
The Paratethys Sea was created through the collisions of moving tectonic plates, explains Sid Perkins in Science. These movements created huge mountains that thrust up and through the existing prehistoric ocean and enclosed one section of it, trapping a massive quantity of ocean water inland. The researchers estimate that the lake’s volume surpassed the astonishing figure of 1.1 cubic miles (1.77 cubic kilometers), which is 10 times more than the volume of water held in all of today’s fresh and saltwater lakes combined.
The remnants of the Earth’s largest lake include Bulgaria’s Cape Kaliakra cliffs (above) overlooking the Black Sea. ( ValentinValkov / Adobe Stock)
How Climate Change Affected the World’s Largest Lake
During the Miocene Epoch, which lasted from 23 million years ago to about five million years ago, the Eurasian climate gradually became dryer. Rainfall levels fell, and the Paratethys Sea was significantly affected by the ongoing climate change. This drying of the climate was not steady, but was instead marked by a series of long-term droughts.
Palcu and his team identified four separate drying events that caused the Paratethys Sea to shrink in size, with the most dramatic shift occurring in the period between 7.9 and 7.65 million years ago. Over this time span the lake lost one-third of its volume and two-thirds of its surface area, with water levels falling by up to 250 meters (820 ft) at areas of greatest depth.
These catastrophic changes caused the salinity of the lake to increase dramatically. This decimated many of the unique species that had evolved there over the nearly five million years the lake had been separated from the world’s larger oceanic ecosystem. “It must have been a post-apocalyptic prehistoric world, an aquatic version of the wastelands from Mad Max,” explained Wout Krijgsman, a geologist and study co-author in a Utrecht University press release .
Smaller versions of dolphins, seals, and whales were among the creatures known to have lived in the Paratethys Sea. Spikes in salinity caused these mammals to go extinct, creating evolutionary dead ends. Only a few of the hardiest species (like certain types of mollusks) were able to survive the changes the lake underwent as its size decreased.
The end came for the Paratethys Sea between 6.9 and 6.7 million years ago. Erosion caused a massive breach in its southwest coastline, forming a rampaging river that eventually drained the lake’s remaining water into the Mediterranean.
Based on the fossil record, scientists know know that the Paratethys Sea was once home to unique species, such as the Cetotherium riabinini, the smallest known whale on record. ( Pavel Gol’Din / Lena Godlevska )
How the Paratethys Sea Shaped the Evolution of African Wildlife
Research by another team of scientists, published in May 2021 in Communications Earth & Environment , has helped publicize the surprising connection between the Paratethys Sea and the evolution and eventual migration of African wildlife.
Fossil finds have shown that the ancestors of giraffes, elephants, and other large mammals that reside on the African savannah originally lived along the southern shores of the Paratethys Sea. They survived by grazing on the grasslands that were formed when the lake’s water levels declined, carving out a niche in a unique ecosystem.
At some point, these large mammals left the area and migrated to the southwest. They eventually settled in Africa and evolved into their modern forms after that. The reason why this migration took place has never been clear, and that motivated evolutionary biologist Madelaine Böhme, from the University of Tübingen in Germany, to launch a study designed to solve this enduring mystery.
The scientists focused their research on western Iran, where the geological record has revealed the occurrence of multiple severe changes in climate during the Miocene Epoch. Examining this record in more detail, they concluded that the animals left because the climate near the rapidly shrinking Paratethys Sea had gradually become too arid for them to survive.
Matching the findings of Palcu’s research team, they identified four distinct phases of significant drying that helped drive the migration, which occurred between 8.75 and 6.25 million years ago. After migrating south and west, these ancient mammals were able to gain a foothold in Africa. The conditions they found closely mimicked those on the grasslands of the ultimately doomed Paratethys Sea, which had played the decisive role in directing the course of their evolution.
The rocky cliffs of Bulgaria’s Cape Kaliakra on the Black Sea. (D.V. Palcu / Utrecht University )
A Lake Dies, But the Land Lives On
Today, the most notable remaining remnant of this magnificent inland lake is the Black Sea , which was formed in the Paratethys’ central basin. Despite its impressive size, the Black Sea covers just 14 percent of the area that the Paratethys did at its prime.
When the Paratethys Sea was extinguished, it completely transformed the interior of Eurasia. With the lake gone, more than a million square miles (two million square kilometers) of fertile new land in Central Europe and Asia were opened for future human settlement. Once they’d dispersed out of Africa millions of years later, humans would eagerly occupy these areas, never dreaming that they were living in a region that had once been submerged under hundreds of meters of water.
Top image: Map showing the location of the ancient Paratethys megalake, known as the Earth’s largest lake. Source: Utrecht University
By Nathan Falde