Our planet's environment is constantly changing, forcing millions of species to adapt to new, often harsh conditions. For example, about 5.5 million years ago, at the very end of the “golden age” for mammals (the Miocene epoch), the Mediterranean Sea almost completely dried up. This geological event, called the Messinian salinity crisis, lasted for at least 640,000 years and left a profound mark on the region's history. It turned out to be due to plate tectonics: the Mediterranean basin, sandwiched between two continents that are still moving closer together by about two centimeters every year, was cut off from the Atlantic. Due to the region's arid climate, its waters quickly evaporated, leaving behind vast quantities of salt.
5.5 million years ago, the Mediterranean Sea did not exist. Image: substackcdn.com
The Messinian salinity crisis was a geological event that saw several cycles of partial or complete drying of the Mediterranean Sea about 5.5 million years ago.
Contents
- 1 How did the sea become a salt lake?
- 2 Extinction of marine species
- 3 Lessons from the mass extinction
- 4 Consequences of the crisis
- 5 Why does the history of the Mediterranean interest scientists?
How did the sea become a salt lake?
What would happen to wildlife if the Mediterranean dried up, turning it into a giant salt lake? The answer to this question has puzzled scientists since the 1970s, when marine geologists and geophysicists discovered a layer of salt between one and three kilometers thick covering much of the deep-sea Mediterranean.
The find is striking evidence of a geologically brief period when the Mediterranean was isolated from the world's oceans. The region's arid climate meant that seawater quickly evaporated, leaving behind vast quantities of salt.
Scientists have discovered nearly a million cubic kilometers of salt in much of the Mediterranean's deep waters. Image: squarespace-cdn.com
The main cause of the Messina Salinity Crisis, as we know it today, was the convergence of the African and Eurasian lithospheric plates. Their movement led to the uplift of the earth's crust in the area of the Strait of Gibraltar, gradually decreasing its depth and width until it closed completely. Without the influx of ocean water, the Mediterranean basin was isolated.
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Thus, the Messina Salinity Crisis became the largest extinction event on Earth since the Chicxulub impact, which wiped out the dinosaurs, ending the Mesozoic era 65 million years ago.
Extinction of marine species
To understand how resilient marine life is to extreme events such as the Messina salinity crisis, scientists from the University of Vienna, in collaboration with the Spanish National Research Council and 28 scientists from 25 European institutes, analyzed data on Mediterranean fossils dating back to between 12 and 3.6 million years ago.
The findings, published in the journal Science, showed that local marine life was nearly wiped out, and subsequent recolonization by Atlantic species led to the emergence of Mediterranean fauna more similar to what is found there today.
The Messinian Crisis had a huge impact on the inhabitants and structure of the Mediterranean Sea. Image: springernature.com
By statistically analyzing information from more than 750 scientific papers, the authors of the study documented the presence of a total of 4,897 marine species living in the Mediterranean Sea, 779 of which are endemic (i.e. they lived only in the Mediterranean Sea). However, only 86 species survived the crisis, including some sardine species and marine mammals related to modern manatees and sea cows.
All the tropical corals that were abundant in the Mediterranean Sea before this catastrophic environmental change disappeared, the authors of the scientific paper noted.
Because the fossil record is limited and fragmentary, scientists cannot be certain that some species were exclusive to the Mediterranean and would not have survived outside of it. Moreover, the question of how some species were able to survive in the face of such a powerful ecological crisis remains open.
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However, the research team managed to establish that the changes in populations are the result of replacement by Atlantic species after the repeated flooding of the Mediterranean Sea, and not rapid adaptation to the new hypersaline environment. In other words, life did not have enough time to adapt and the Atlantic species replaced the extinct ones.
A huge number of species disappeared from the face of the Earth as a result of the Messinian salinity crisis. Image: i.turkiyetoday.com
At the same time, several species, such as the great white shark and the dolphin, appeared in the Mediterranean Sea only after the Messinian crisis. Even more interesting is the fact that the current wealth of the Mediterranean fauna appeared only after the repeated flooding – previously, the Ionian and Levantine seas were distinguished by a large number of different species.
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Lessons of mass extinction
The results of the new scientific work also showed that it took more than 1.7 million years for the number of species to recover. The slow recovery of the Mediterranean's ecosystem richness provides the first detailed, quantitative picture of how wildlife responds to a die-off of this magnitude.
The researchers note that the Mediterranean Sea is extremely rich in biodiversity today, thanks to the presence of numerous endemic species. This was also the case six million years ago, but the vast majority of endemic species disappeared when the sea became isolated from the Atlantic.
The Mediterranean Sea and its inhabitants can tell us a lot about geological processes on our planet. Image: timesofisrael.com
It should also be noted that geological processes on Earth tell scientists much more about its past than any laboratory experiments.
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Today, as we know, a huge number of animal and plant species are under threat of extinction due to climate change and environmental pollution. The data of the new study, in turn, showed that marine flora and fauna recover from crises slowly and for a long time.
Consequences of the crisis
The consequences of the Messinian salinity crisis were obviously reflected in the vegetation and land animals. Some species were forced to adapt to the new conditions, which stimulated evolutionary processes, and the exposure of the seabed, for example, created new ecosystems adapted to high temperatures and salinity.
Interestingly, when the crisis ended, tectonic processes and rising sea levels caused the Strait of Gibraltar to reopen, causing a massive influx of water from the Atlantic Ocean. According to some models, water could have filled the dried-up Mediterranean basin in just a few months or years, with the flow rate through the Strait of Gibraltar reaching 100 meters per second, creating one of the most powerful waterfalls in the history of the Earth.
The history of the Mediterranean Sea is mind-boggling. Image: earth.com
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Thus, the study of the Messinian salinity crisis is important for understanding global geological and climatic processes on Earth and serves as a natural experiment that allows us to study the responses of ecosystems to extreme environmental changes.
Why does the history of the Mediterranean interest scientists?
The events of 5.5 million years ago remind us how quickly and dramatically environmental conditions on the planet can change. Although the Messinian salinity crisis is caused by natural tectonic processes, it demonstrates the vulnerability of ecosystems to abrupt changes. In the context of modern environmental issues such as climate change, studying this period is particularly relevant.
The Messinian salinity crisis is one of the most fascinating and significant events in the geological history of the Earth. Image: i.turkiyetoday.com
What happened to the Mediterranean Sea 5.5 million years ago continues to intrigue scientists and the public, reminding us of nature's ability to transform the planet itself. Studying this period not only enriches our knowledge of the Earth's past, it also provides valuable lessons for the present and the future.