A large land bridge formed 20 million years ago that connected continents, shaped climates, divided oceans and changed the course of evolution.
That’s according to a recent paper published in Nature Reviews Earth & Environment. It brings together multiple disciplines – including plate tectonics, evolutionary anthropology and climate studies – to provide what the researchers call a “provocative” summary of current research on the Tethys Seaway closure.
Earth used to look completely different 30 million years ago. Africa was isolated from other continents, and an enormous ocean – called Tethys – spanned all the way from the Atlantic to the Indo-Pacific oceans, via what is now the Mediterranean.
But around 20 million years ago, a land bridge formed between Africa and Asia for the first time, splitting the Tethys Sea into the Mediterranean and Arabian Seas.
This allowed mammals – such as our ancestors, giraffes and elephants – to travel out of Africa into Asia and Europe, and it profoundly shaped the evolution of creatures and plants on land and in the sea.
The study explains how scientists believe this land bridge formed. Approximately 50 to 60 million years ago, a slab of rock slid into the Earth’s mantle, creating a 'conveyor belt' for hot rocks to boil up in an underground plume.
Roughly 30 million years later, these hot rocks reached the surface as tectonic plates collided, and this resulted in the uplift of a section of land that joined Africa to Asia for the first time in 75 million years.
“Without the plume, you could argue that the continental collision would have been different,” said Eivind Straume, the study’s lead author and, at the time of the study, a postdoctoral fellow at the University of Texas at Austin’s Jackson School of Geosciences, in the US, in a statement.
“It’s an example of how the long-term convective evolution planet talks to the evolution of life.”
If the land bridge had formed at a different time, the researchers said, the animals that travelled between the African and Asian continents could have been on a different evolutionary path – including the ancestors of modern humans.
They wrote that the closure of the Tethys Seaway had a major impact on the Earth's climate too, triggering the desertification of the Sahara, the intensification of monsoon season in Southeast Asia and the diversification of marine habitats.
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