More oxygen from new layer in Earth’s mantle

An international group of scientists have discovered a layer in the Earth’s mantle, which they estimate contains around eight to ten times more oxygen than Earth’s atmosphere. The existence of such a layer was previously unknown.

“This discovery came as a big surprise to us and so far we don’t know what is happening to these ‘rivers of oxygen’ in the depths of our planet,” said Elena Bykova, a member of the group of scientists who made the discovery.

Scientists believe that the free oxygen rivers could either react with surrounding materials and oxidize them, or rise to the upper layers within the mantle. The discovery of this accumulation of free oxygen inside the mantle happened when scientists were studying the reactions of various types of iron oxide, one of the main components of deep-seated rocks.

So how does the mantle happen to have so much free oxygen?

“As we all know, free oxygen in the atmosphere is produced by the photosynthesis of plants,'' said Innokenty Kantor, senior researcher in the physics department of the Technical University of Denmark."Before the rapid development of photosynthetic bacteria billions years ago, surface conditions on Earth were changing, and ocean water was full of dissolved iron compounds. As soon as free oxygen was released at that time, it immediately reacted with reduced iron, producing iron oxide sediments, in other words, rust, at the bottom of oceans.”

According to Kantor, an enormous amount of such deposits formed after the ‘Great Oxygen Event’ about 2.4 billion years ago, when oxygen appeared in the atmosphere. Such deposits were several hundred metres thick and hundreds of miles long. These deposits then slowly sank into the mantle, but hundreds of millions of years later some parts were pushed to the surface and exposed, such as the Kursk Magnetic Anomaly, the largest iron ore basin in the world. But most of the oxygen remained trapped in Earth's deep interior.

Scientists today can reproduce extremely high pressure and temperature in a lab, using small presses with miniature anvils made of diamonds and high-powered lasers. 

“Iron oxide, Fe2O3, partially decomposes under conditions of the lower mantle, and releases an enormous amount of oxygen (many times the atmospheric content), which should be liquid at the corresponding conditions,” Kantor said.

These highly oxidizing fluids that infiltrate the mantle could affect many geo-chemical processes, although their exact role is yet to be understood. According to Kantor, some of the minor anomalies of seismic wave propagations at the depth of 1,500-2,000 kilometres could also be related to the formation of liquid oxygen lakes in the deep mantle of the earth.

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