4.5 billion years ago a planet crashed into Earth – National Geographic France

The hypothesis is anything but unanimous. “In our simulations, the mantle of Theia and the Earth’s mantle mixed quite well,” testifies planetary scientist Miki Nakajima of the University of Rochester in New York. In recent years, his work has focused on the evolution of the internal structure of the rocky planets in our solar system.

“I don’t think the impactor material would have mixed completely, but the degree of homogenization is underestimated in this study,” adds geodynamicist Maxim Ballmer from University College London. Although Ballmer is not associated with the recent study published in the journal Nature, he collaborated with Deng on a similar study several years ago.

Scientists are aware that these higher-density regions have long inhabited the Earth’s mantle, but their exact age and origin are still controversial.

“There is an alternative explanation for the formation of these superplumes,” adds Ballmer. In particular, he mentions a theory that the solid mantle we know today was once a thick layer of molten magma before differentiated into the layers we see today. The top layer quickly solidified and radiated its heat into space. According to certain studies, the lower layer solidified more slowly and therefore had time to form more or less dense regions.

The next step will be to compare the chemical signatures of the materials present in these superplumes and on the moon, which is largely made up of Theia. “If they have the same geochemical fingerprint, they must come from the same planet,” Yuan says.

However, collecting new samples is easier said than done. It is impossible to drill the earth into superplumes. However, as Yuan explains to us, rocks from the lower mantle sometimes reach the surface, particularly in the case of basalts from oceanic islands.

The Moon’s surface has been subject to space erosion for billions of years and is at risk of being contaminated by meteorites; Researchers would therefore also like to analyze samples from the lunar mantle. The data so far comes mainly from the surface.

To obtain new fragments of the Moon, we must wait for a future sample return mission to the South Pole, where the mantle is clearer and more accessible. Until then, scientists will continue to refine their models to try to identify Theia’s spectrum.