Our planet could be left without 40% of its material due to the collisions with other bodies occurred during its formation stage. This would explain the changes in their chemical composition

Chondrites, a very common meteorite – the one that fell in Chelyabinsk (Russia) in February 2013 – was one of them – reflect the conditions of the primitive Solar System and are considered the building blocks of the Earth. However, our planet and other comparable ones, like Mars, show a different composition to those rocks. The motif is one of the great mysteries of planetary science.

Although some explanations have been proposed in this regard, none has been able to take into account all the differences. Now, two new independent research papers published in the journal Nature seek to clarify the enigma of the particular composition of our world from a new perspective. According to the researchers, what happened is that the Earth lost almost half of its composition when its molten rock evaporated when it was still forming.

The planets grow through a process of accretion, a gradual accumulation of additional material, at the same time as they collide with their neighbors in a kind of violent game of billiards at the cosmic level. This results in a very chaotic process and the material is continuously gained and lost. Massive planetary bodies that hit several kilometers per second generate heat that in turn produces magma oceans and temporary atmospheres of vaporized rock.

Before the planets reach approximately the size of Mars, the gravitational pull is too weak to remain in this silicate atmosphere. When hitting other bodies, that vaporized material is lost and the composition of the planet changes substantially.

“We have provided evidence that such a sequence of events occurred in the formation of Earth and Mars, using high-precision measurements of their compositions of magnesium isotopes,” explains Remco Hin of the Earth Sciences School of the University of Bristol and responsible for one of the research appearing in Nature.

“The proportions of magnesium isotopes change as a result of the loss of silicate vapor, which preferably contains the lighter isotopes. In this way, we estimate that more than 40% of the Earth’s mass was lost during its construction, “he adds. And that is the motive “of the unique composition of the Earth”

Samples of Mars and Vesta
To reach that conclusion, the researchers analyzed samples of the Earth along with Mars meteorites and the asteroid Vesta (all three bodies have different proportions of magnesium isotopes), using a new technique to obtain more precise measurements of the magnesium isotopes that those obtained previously. According to Hin, the work “changes our views on how the planets reach their physical and chemical characteristics.”

“While it was previously known that the construction of planets is a violent process and that the compositions of planets such as Earth are different, it was not clear that these characteristics were linked. Now, we show that the loss of vapor during high energy collisions of planetary accumulation has a profound effect on the composition of a planet, “says the researcher.

For Hin, this process seems common to planet-building in general, not only for Earth and Mars, but “for all the planets in our solar system and probably beyond”, but the differences in their collision histories will create a diversity in their compositions.

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