Washington (AFP)

Water covers 70% of the Earth's surface and is crucial to life, but how it got there is the subject of an old scientific debate.

A team of French researchers contributed to the building on Thursday by asserting that our planet would have been, from its origin, rich in water, probably contained in abundance in the rocks that made it up.

Cosmochemist Laurette Piani, who led this study by the Center for Petrographic and Geochemical Research (CNRS / University of Lorraine) published in the journal Science, explained to AFP that this discovery undermined the dominant thesis that water would have been brought later by asteroids and comets having bombarded an initially dry Earth.

This hypothesis was favored by the excessively high temperatures of the Solar System which would have prevented water from condensing and agglomerating with other solids in the form of ice.

French researchers looked at meteorites called enstatite chondrites which have the particularity of having a chemical composition close to that of the Earth. This indicates that they are similar to the rocks that were part of it from its formation.

By measuring the hydrogen content of 13 of these relatively rare meteorites, the team found that the primitive rocks of the blue planet detected enough hydrogen to provide it with at least three times the mass of water in its oceans, if not more.

"We found that the isotopic composition of hydrogen in enstatite chondrites was similar to that of water stored in the Earth's mantle," said Laurette Piani.

The isotopic composition of the oceans is for its part compatible with a mixture containing 95% water of these chondrites, an additional element supporting the thesis according to which they are at the origin of terrestrial water.

The authors also found that the nitrogen isotopes of these meteorites are similar to those of nitrogen from Earth.

According to Laurette Piani, this study does not exclude further water supply from other sources, such as comets, but it does insist that enstatite chondrites have contributed significantly since the formation of the planet.

This work "brings a crucial and elegant piece to this puzzle", wrote Anne Peslier, researcher at NASA, in an editorial accompanying the study.

© 2020 AFP