Emergence of a land bridge 20 million years ago allowed elephants and humans to cross into Asia, and turned the Sahara into a desert

What happens beneath the Earth’s surface may seem distant, but its effects shape continents, influence ocean circulation, climate patterns, and even the evolution of life. An international team of scientists has discovered that a plume of hot rock rising from the Earth’s mantle millions of years ago may have been a key factor in the evolution of human ancestors and the formation of key ecosystems.

According to research published in Nature Reviews Earth & Environment, the gradual uplift of a vast region that now includes the Arabian Peninsula and Anatolia created a land bridge between Asia and Africa 20 million years ago. This phenomenon ended 75 million years of isolation for the African continent, allowing species such as giraffes, elephants, rhinoceroses, cheetahs, and the earliest primate ancestors of humans to migrate between the two landmasses.

The study, led by Eivind Straume — currently a researcher at the NORCE Norwegian Research Centre and The Bjerknes Centre for Climate Research — combines geological models developed at the University of Texas at Austin and the GFZ Helmholtz Centre for Geosciences with previous research. The results suggest that this geological event not only changed the distribution of life, but also altered the global climate and ocean circulation.

A process spanning millions of years

The story begins between 50 and 60 million years ago, when a slab of rock sank into the Earth’s mantle, triggering a kind of “conveyor belt” that pushed hot material toward the surface. Thirty million years later, this mantle plume — along with the collision of tectonic plates — raised the terrain, gradually closing the ancient Tethys Sea.

This body of water split into what are now the Mediterranean and the Arabian Sea, while the newly emerged land linked Asia and Africa for the first time.

The closure of this marine corridor occurred millions of years earlier than expected due to these specific processes: mantle convection and changes in dynamic topography, Straume explained. Without the plume, the continental collision would have been different.

The precise moment that defined evolution

The study highlights that timing was a critical factor. If the connection between Africa and Asia had been delayed by a million years, the species that crossed — including the primates that gave rise to humans — might have followed a different evolutionary path.

According to the researchers, a few million years before the land bridge became established, the first primates arrived in Africa from Asia. Although their relatives in Asia went extinct, their descendants in Africa thrived and diversified. When the bridge was fully formed, these primates recolonized Asia.

It’s an example of how the long-term convective evolution of the planet interacts with the evolution of life, Straume noted.

Climate impacts and the desertification of the Sahara

The uplift of the Arabian Peninsula affected not only species but also the climate. Nearby ocean temperatures rose, expanding seasonal ranges and making regions from North Africa to Central Asia more arid. The researchers believe that this event was the final trigger for the desertification of the Sahara.

Additionally, topographic changes intensified the monsoons in Asia, increasing rainfall in the southeastern part of the continent.

The study synthesizes research in fields as diverse as plate tectonics, mantle convection, paleogeography, evolutionary anthropology, and climatology. According to Thorsten Becker, co-author of the study and professor at the University of Texas, the work offers a provocative but compelling synthesis of recent advances. The relevant question is: How did our planet change overall? What are the connections between life and tectonics?, Becker reflected.

The findings underscore how deep geological processes can have unpredictable consequences on the surface — from the formation of deserts to the fate of our ancestors. Once again, Earth proves that its geological and biological histories are inextricably intertwined.

SOURCES

The University of Texas at Austin

Straume, E.O., Faccenna, C., Becker, T.W. et al. Collision, mantle convection and Tethyan closure in the Eastern Mediterranean. Nat Rev Earth Environ 6, 299–317 (2025). doi.org/10.1038/s43017-025-00653-2