The green serpentinite stone, similar to snakeskin and with a liquid in its structure, was believed to have been a key driver in the recycling of oxygen and helped create an atmosphere for life on Earth.

The Earth is constantly in a cycle of processing water and oxygen, on which life literally depends, when tectonic plates sink deep into the planet’s body. Elements are pulled downward when parts of the crust displace each other, and then “float” to the surface through active volcanoes.

“This cycle is very important. It contains information on how much oxygen is above the surface and how this volume is changed and maintained by subduction, ”says Esteban Gazel, associate professor in the Department of Earth and Atmospheric Sciences at Cornell College of Engineering. Although this cycle is known, the details of the process – how exactly subduction reproduces oxygen – has always been a matter of debate.

Previously, researchers looked for clues by measuring oxygen levels in the Earth’s mantle – a layer under crust filled with magma. It was possible to look there thanks to the volcanoes. Some geologists have noted that oxidation is intensifying beneath volcanic arcs, where the hydrated oceanic lithosphere sinks into the mantle. The leading theory included the oceans as the main factor: the water bringing hydrogen into the mantle influenced the oxidation process. But in the new study, everything is different: oxygen enters the mantle with fluids squeezed out by pressure and heat from serpentinite.

Under the oceans and seas, the process of serpentinization (when ultrabasic rocks are transformed into others under the influence of thermal aqueous solutions) creates stones, inside of which are oxygen-saturated liquids. And then these stones are absorbed by the mantle of the Earth.

Sooner or later, these serpentinite juices are squeezed out of the tectonic plate. If the plate moves and stands at the right angle, fluids flow out and oxygenate the mantle beneath the volcanoes. Moreover, in the cold zones of subduction, oxidation is even more active.