Earth’s early oceans were saltier than they are today

Scientists at Yale University say Earth’s ancient oceans were saltier than they are today – a discovery that could help us understand how life, the atmosphere and climate evolved on the planet.

In a new study, experts suggest that during the first 500 million years of Earth’s existence, its oceans may have contained a salt level of 7.5%. By comparison, today’s oceans contain about 2.5% salt.

Previous estimates of primordial ocean salinity, all based on indirect data, have ranged from the current level up to ten times higher.

“This is just the beginning of deciphering the chemistry of the primordial ocean, where many other unknowns exist, but we now have a solid foundation to build on,” said John Korinaga, professor of Earth and planetary sciences at Yale University, one of the study’s authors. .

This study was published in the Proceedings of the National Academy of Sciences.

The scientists began their investigations with a broader and more fundamental question in mind. They wanted to know how much stable halogens — elements such as fluorine, chlorine (found in salt), bromine and iodine that when they react with metals and produce a variety of salts — are present on Earth.

Halogens play a critical role in some fundamental processes related to planet formation and evolution, including how Earth’s atmosphere, oceans, and lithosphere interact. The presence of halogens in seawater is especially important, given the fundamental nature of the oceans to make life on Earth possible.

To date, estimates of the global abundance of halogens have been based on the assumption that the proportion of some elements in the crust and mantle – the rocky layer 3,000 km thick – has stability throughout the melting and crystallization period, and these estimates suggest that most of the halogens are found near the surface.

That’s not the case, say Yale University scientists. They have devised a new method for estimating global halogen levels, based on a new computational tool and the latest science on how other elements circulate through the Earth’s surface and inner layers.

The new discovery indicates that chlorides and other halogens were largely expelled from the planet’s interior during Earth’s first 500 million years – bringing them closer to the crustal surface of Earth and oceans – and then pushed back into the mantle.

“Our finding is completely against conventional wisdom,” Korenaga said.