Earth's history Separation of the Mediterranean and Atlantic caused species to become extinct

Only one in ten species native to the Mediterranean survived the separation of the Mediterranean and Atlantic 5.5 million years ago. An international research team with the participation of the Natural History Museum Basel has quantified this loss of species for the first time.

It took 1.7 million years for biodiversity to recover after this ecological crisis, as the Natural History Museum Basel announced on Friday. The study, led by the University of Vienna (Austria), was published in the journal "Science" on Thursday evening.

According to the museum, a kilometer-thick layer of salt under the Mediterranean still bears witness to the crisis around 5.5 million years ago. At that time, the Mediterranean lost its connection to the Atlantic due to plate tectonic shifts and thus an important water supply. Similar to the Dead Sea today, the Mediterranean Sea became increasingly salty as a result and dried up almost completely at times. Researchers call this event the "Messinian salt crisis".

Traces still visible today

In order to find out what effect the salt crisis had on biodiversity, the researchers analyzed over 22,000 fossils, as the study shows. The results showed that two thirds (67 percent) of the species previously native to the Mediterranean no longer appeared in the samples after the crisis. Of the species that lived exclusively in the Mediterranean before the crisis, only eleven percent survived.

According to the press release, it took longer than the researchers had expected - 1.7 million years - for the number of species to recover.

Once the connection to the Atlantic was re-established, new species migrated from the west - i.e. from the connection to the Atlantic. This process of recolonization after the crisis is still visible in the Mediterranean: the diversity of species in the northwest is still higher than in the southeast of the sea.