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Earth’s inner core may be rich in oxygen

Oxygen is essential for life and is one of the most abundant elements on Earth. The amount of oxygen in the Earth’s atmosphere makes it a habitable planet.

However, it is still unknown whether (and in what form) oxygen exists in the inner core of our planet, which consists of almost pure iron, where conditions of extremely high pressure and high temperature prevail.

Scientists led by Dr. Jin Liu of the Center for Advanced Research in High Pressure Science and Technology (HPSTAR) and Dr. Yang Song of Columbia University found that iron-rich Fe-O alloys are stable at a maximum pressure of 300 GPa and temperatures. reaches over 3000 Kelvin.

The results, published in The Innovation, demonstrate that oxygen can exist in a solid inner core, creating fundamental limitations to understanding the formation and evolutionary history of the Earth’s core.

The solid inner core of the Earth, as one of the most mysterious places on the planet, is at the most extreme temperature and pressure on our planet, with a pressure of more than 3 million atmospheres and a temperature close to the surface of the Sun. , about 6000 kelvins.

Because the inner core is far beyond human reach, we can only infer its density and chemical composition from the seismic signals generated by earthquakes.

The light elements are now believed to be present in the inner core, but the type and content is still a matter of debate.

Cosmological and geochemical data indicate that it must contain sulfur, silicon, carbon and hydrogen.

Experiments and calculations have also confirmed that these elements mix with pure iron to form various iron alloys at high temperatures and high pressure conditions deep in the earth.

However, oxygen is usually excluded from the inner core, mainly because iron-rich Fe–O alloys never occur in surface or mantle environments. The oxygen content in all known iron oxides is greater than or equal to 50 atomic percent.

Although scientists have tried to synthesize iron oxide compounds with an iron-rich composition, no such material has yet been found.

And to answer the question: is the Earth’s inner core “not enough oxygen”? In this work, a number of experiments and theoretical calculations were carried out.

To approach the temperature and pressure of the Earth’s core, pure iron and iron oxide were placed on the tips of a diamond anvil and heated with a high-energy laser beam.

After many attempts, it was found that the chemical reaction between iron and iron oxide occurs above 220-260 GPa and 3000 K.

The results show that the reaction product is different from the usual composition of pure iron and iron oxide at high temperature and high pressure.

A theoretical study of the crystal structure using a genetic algorithm has shown that an iron-rich Fe-O alloy can stably exist at a pressure of about 200 GPa. Under these conditions, iron-rich Fe-O alloys form a packed hexagonal structure in which oxygen layers are placed between iron layers to stabilize the structure.

Source: phys.org.


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