Carbon in the Earth's biosphere could have appeared as a result of its collision with an embryonic planet, similar to Mercury. This is evidenced by the results of a study conducted by petrologists from Rice University.
The earth was formed about 4.5 billion years ago. According to modern concepts, the first atmosphere of the planet was formed due to volcanic degassing and did not contain oxygen. The second is due to the degassing of volatile substances (carbon, hydrogen, sulfur, nitrogen) from the depths or bombardment by asteroids and comets, the third is due to bacteria. But the question of the emergence of a second atmosphere and conditions suitable for life remains open.
In particular, the mechanism of carbon origin is unclear. In theory, due to the high temperature on the surface, it should have evaporated in the early days or be trapped in the core of the planet. The theory that volatiles appeared in the biosphere due to collisions with comets and asteroids after the formation of the nucleus is also controversial. So, scientists do not know meteorites, the concentration of volatiles in which is identical to the composition of the Earth's mantle.
In the new work, the authors modeled the conditions of high pressure and temperature, which are characteristic of the mantle of the terrestrial planets. The goal of the scientists was to analyze how certain substances contribute to the release of carbon from the iron-nickel core of the Earth into the mantle. The results showed that this is possible if the alloy of the core is rich in silicon or sulfur. It is assumed that the core of Mars is rich in sulfur, while that of Mercury is rich in silicon.
“In one scenario that explains the current carbon-sulfur ratio in the mantle and the abundance of carbon in the biosphere, an embryonic planet like Mercury collided with Earth and was swallowed up by it. Due to its large size, the core of this planet, rich in carbon, could go to the core of the Earth and mix with it,”said research facilitator Rajdip Dasgupta. He added that this could have happened about 4.4 billion years ago.