What if the Great Oxidation had a geological origin?

If you are interested in the origin of life on Earth sooner or later you will find the phenomenon known as the Great Oxidation, about 2400 million years ago. The Great Oxidation was a radical change in the Earth's atmosphere in which it began to contain significant amounts of oxygen or, as the chemists say, it went from being reductive to oxidizing. Life, as we know it today, is a consequence of adaptation to this circumstance and would have been other forms of life, the cyanobacteria, which 2800 million years ago would have caused that atmospheric change to be the first photosynthetic creatures capable of produce molecular oxygen.

But what if this, which is in any textbook, would not have been like that? An international team led by Ho-kwang "Dave" Mao, of the Carnegie Institution (USA), proposes another idea based on a purely geological phenomenon. In this phenomenon, only water, iron, and the high pressures and temperatures of the interior of the Earth intervene.

Source: National Science Review.

When the action of plate tectonics brings minerals containing water into the interior of the planet until it meets the iron core of the Earth, the extreme conditions of pressure and temperature cause the iron to take oxygen atoms from the water molecules and release the hydrogen atoms. Hydrogen escapes to the surface, but oxygen is trapped forming crystalline iron dioxide, FeO2, which can only exist at these intense pressures and temperatures.

Using theoretical calculations and laboratory experiments to recreate the core-mantle boundary environment, the team determined that iron dioxide can be created effectively, using a diamond-heated diamond anvil cell to expose materials to between 950 and 1 million times the normal atmospheric pressure and 2000 ºC of temperature.

Source: National Science Review.

Researchers estimate that 300 million tons of water could be transported to the core iron and generate huge iron dioxide rocks each year. These extremely oxygen-rich rocks could accumulate year after year above the core, growing to colossal sizes, like those of a continent. A geological event that heated these iron dioxide rocks could cause a massive eruption, suddenly releasing a large amount of oxygen to the surface.

The authors hypothesize that if an oxygen explosion of this type could inject a large amount of gas into the Earth's atmosphere, nothing would prevent it from being the cause of the Great Oxidation, the driving force of oxygen-dependent life that we know .

This discovery can have many more consequences for geochemistry. This hydrolysis, the term that chemists use to refer to the breakdown of the water molecule, at high pressure and tempertaura, would affect geochemistry from the depths of the Earth to, as we have seen, the atmosphere. We have to review many theories.

Reference:

Ho-Kwang Mao et al (2017) When water meets iron at Earth’s core–mantle boundary National Science Review doi: 10.1093/nsr/nwx109