Under the ocean, the movement of the continents has orchestrated the evolution of life

Beneath the ocean, the movement of the continents orchestrated the evolution of the living

MISE À DAY

Since the dawn of life on Earth, marine biodiversity has evolved through oxygenation from the movements of the continents, and not just from the atmosphere, according to a study published Wednesday in Nature.  

Scientists have managed, thanks to 3D modeling, to go back to the oldest geological times to trace the evolution of the oceans for about 540 million years.

It was at the beginning of this so-called Cambrian period that the first forms of complex life appeared – beyond simple unicellular organisms – such as trilobites, these marine arthropods that disappeared during one of the first mass extinctions.

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“The major plans for the organization of living things, namely life as we know it today, emerged 500 million years ago,” paleoclimatologist Alexandre Pohl told AFP. CNRS researcher at the Biogéosciences laboratory (Dijon) and main author of the study.

Then, during the Ordovician, 460 million years ago, biodiversity experienced a real explosion. Probably thanks to the oxygenation of the waters, where the oxygen concentration levels made the places conducive to the development of fauna.

It is commonly believed that this “marine oxygenation” results from changes in oxygen in the atmosphere. But by refining several existing climate models, Alexandre Pohl and his team discovered that these evolutions were also largely dictated by plate tectonics, the movements of reorganization of the position of the continents.

They carried out numerical simulations of ocean currents, modified by plate tectonics, which show a “major decoupling between the oxygenation of the superficial and deep ocean”, explains the researcher from the University of Bourgogne-Franche Comté.

< p>Their model thus suggests that before the Ordovician biodiversity explosion, the deep ocean was poorly oxygenated even though the concentrations in the atmosphere were already relatively high. A sign that the oxygenation of the deep waters then intervened through the geological movement of the plates, independently of what was happening in the air.

540 million years ago, the supercontinent which preceded the Pangea, called the Pannotia, was beginning to fall apart. Throughout the reconfigurations, which span millions of years, the levels of marine oxygen have varied, probably playing a key role in the evolution of species.