Boffins rewrite the book on how Earth's oceans developed

You don't need alien asteroids, you just need a hydrogen-rich atmosphere and liquid hot magma

A new research model shows that Earth's oceans could have formed from interactions between a hydrogen-rich early atmosphere and oxygen within the planet's magma.

The study from the multi-institution AETHER project also demonstrates why Earth's core is lighter than it should be, owing to the presence of gaseous hydrogen.

Edward Young, professor at the University of California Los Angeles, and colleagues propose that one of the protoplanets involved in the formation of Earth was heavier than thought. By maximizing its size to more than a fifth or third of Earth, the researchers show there would have been enough gravity to make the hydrogen-rich atmosphere hang around long enough to interact with the magma ocean, according to a paper published in Nature this week.

Prevailing theories explaining the abundance of water on Earth – oceans make up around 70 percent of the planet's surface – depend on the impacts of water-carrying asteroids.

In an accompanying article, Sean Raymond, researcher at France's Laboratoire d'Astrophysique de Bordeaux, said: "By revising the idea that Earth's largest protoplanets were as small as Mars, Young et al have proposed a way in which hydrogen gas could have mixed into Earth's mantle before it solidified, affecting the entire planet through convection. This suggests that gaseous hydrogen is the light element responsible for the low density of Earth's core."

Magma is made up mainly of oxygen and molten silicon. "The authors have demonstrated that early interactions between magma oceans and atmospheres represent a key ingredient in future models of how Earth was shaped," Raymond said.

The author's calculations show that interactions with atmospheric hydrogen could produce enough water to fill the current volume of our oceans three times over.

In a statement coinciding with the publication, co-author Anat Shahar, staff scientist and deputy for Research Advancement Earth and Planets Laboratory at Carnegie Science, said the inspiration for the new model came from studies of planets forming outside the solar system.

"Exoplanet discoveries have given us a much greater appreciation of how common it is for just-formed planets to be surrounded by atmospheres that are rich in molecular hydrogen during their first several million years of growth. Eventually, these hydrogen envelopes dissipate, but they leave their fingerprints on the young planet’s composition," she said.

"This is just one possible explanation for our planet's evolution, but one that would establish an important link between Earth's formation history and the most common exoplanets that have been discovered orbiting distant stars, which are called Super-Earths and sub-Neptunes," Shahar said. ®