The newborn Earth "ate" several embryos of the planets after its collision with Theia, the progenitor of the Moon, traces of which geologists have found in the oldest rocks of the planet in Greenland, according to an article published in the journal Nature Geoscience.
“We built computer models of how the newborn Earth collided with other celestial bodies, and how their metals and silicates mixed with the matter of our planet during what we call the 'era of late accretion'. These calculations show that the interior of the Earth contains much more of this matter than our colleagues believed. This changes the history of its evolution dramatically, said Simone Marchi of the Southwest Research Institute in Bowder, USA.
Riddles of the Moon
For the past 30 years, it has been generally accepted that the Moon was formed as a result of the collision of Theia, a protoplanetary body, with the "embryo" of the Earth. The collision led to the release of the matter of Theia and the proto-Earth into space, from this matter the Moon was formed. The theory of the collision of the proto-Earth with a large celestial body explains well the mass of the Moon, the low iron content on it, and other parameters.
However, in such a collision, a significant part of the material that makes up the moon should have come from the hypothetical Theia. In its composition, it should have been different from the Earth, as most of the celestial bodies of the inner region of the solar system, which includes the terrestrial planets and asteroids, differ from it. But in fact, the composition of the Earth and the Moon is very similar, up to the same proportion of isotopes of many metals and other elements.
Despite all the advantages of this hypothesis, it has several serious disadvantages. For example, in accordance with this idea, all water reserves should have completely evaporated from the matter of the future Moon at the moment when it was thrown into space after the collision of Theia and the Earth.
Six years ago, many astronomers began to doubt this, since the proportions of water in some of the rock samples brought to Earth by the Apollo 15 and Apollo 17 expeditions were hundreds of times higher than theoretically predicted values. Other scientists have suggested that NASA astronauts stumbled upon some kind of "water anomaly", which may not have analogues on the Moon.
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Markhi and his colleagues suggest that almost all of these anomalies could be caused by the fact that the Earth collided not only with Theia, but also with many other embryos of planets, a significant part of the matter of which is now hidden in the bowels of our planet.
Space Meal Traces
They came to this conclusion by creating a computer model of the newborn solar system, which was inhabited not only by the Earth and the Moon, but also by many planetisimals, "dead" embryos of planets that periodically collided with our planet and other celestial bodies.
Scientists believe today that the Earth had to survive dozens or even hundreds of such collisions. Most of the matter of such planetary embryos had to evaporate into space or be thrown out there during a collision with the Earth, as a result of which only 0.5% of its mass today falls on the matter of "alien" worlds.
The calculations of Markha's team showed that this is not the case. If at least a small part of these planetisimals were large enough, more than 1500 kilometers across, then the Earth's interior consists of about 2.5-3% of rocks formed in the bowels of other planets.
How to find traces of these planets? According to geologists, the force of these collisions was not high enough for the crust and mantle of the Earth to completely melt and mix with "alien" rocks, but it was enough for the fragments of the former embryo of the planet to penetrate to great depths.
This means that in the interior of the planet there should be regions with anomalous proportions of isotopes of various metals, such as tungsten and hafnium, as well as unusual silicate rocks, the analogs of which do not exist anywhere else on our planet. Markhi and his colleagues believe that their deposits are found in Greenland, in the so-called greenstone belt.
Here, according to them, unique komatite rocks are often found, containing abnormally high proportions of tungsten-182 and having an unusual structure that are not found anywhere else on Earth. Their study, according to Markhi, will help us understand how many other planets the Earth "ate" and how it looked in the first moments of its life.