Effects of the influence of the Moon’s formation on the Earth’s mantle

Deep traces of the primordial mega-impact? Known density anomalies in the Earth’s interior could be the remains of the celestial body that formed the Moon after its collision with the primordial Earth. This arises from new simulations of the dynamics and mixing processes during the suspected collision about 4.5 billion years ago. Scientists say the results shed light on the causes of Earth’s internal structures and on early evolutionary processes in the solar system.

How did our home planet’s companion form? This question has puzzled scientists for generations. This embellished origin story is now the prevailing theory: According to this theory, the Moon formed from debris formed about 4.5 billion years ago when the primordial Earth Gaia collided with a Mars-sized protoplanet called Theia. The assumptions are based on simulations of the processes that would have occurred during and in the aftermath of the massive impact. However, there are still some unclear aspects of this impact theory and the remains of Theia are unknown. Until now, previous research has mostly focused on the formation of the debris disk, the Moon’s primary material. However, the effects of a giant impact on early Earth have received less attention.

How did the collision shape the Earth?

An international team led by Qian Yuan of Arizona State University in Tempe has now dedicated itself to this topic. Scientists investigated the question of how a collision could have led to certain distributions of material from both partners in the newly formed Earth. Specifically, their focus was on known density anomalies in the Earth’s interior, the cause of which is currently a mystery. These are two so-called large low-velocity provinces (LLVPs), which extend thousands of kilometers apart at the base of the Earth’s mantle. One is under the African tectonic plate and the other is under the Pacific tectonic plate. Previous seismic studies have shown that these are accumulations of material significantly denser than the surrounding rock.

Scientists have now investigated the hypothesis that LLVPs could be leftover material from the celestial body that Theia collided with. To do this, they developed complex simulation models that show the dynamic processes after a collision. The goal was to illustrate what would happen to certain components of collision partners. The researchers presented evidence that the material in Theia’s mantle was slightly richer in iron, and thus heavier, than that of ancient terrestrial Gaia.

The sunken remains of Theia

As the team reports, their model simulations now show that a significant amount of Theia material could indeed reach Gaia’s lower mantle. Specifically, the collision appears to have generated numerous molten Theia clumps several tens of kilometers in diameter. Due to its relatively high density, it slowly sank into the solid mantle of Gaia. Eventually, they coalesced in the region of the transition zone to the Earth’s core and thus formed long-period LLVPs, as indicated by the geodynamic model simulation results.

Scientists explain that these structures were largely spared from further geological developments on Earth, and thus have survived to this day. In other words: the previously mysterious LLVPs could be remnants of Theia and thus tangible traces of the massive collision that led to the formation of our moon.

The findings shed light on the evolutionary history of our home system — and beyond. “Because giant impacts frequently occur in the final stages of planet formation, it is possible that similar mantle anomalies caused by impacts could also arise in the interiors of other planets,” the team concludes. . bodies,” write Yuan and his colleagues.

Source: Chinese Academy of Sciences, specialized article: Nature, doi: 10.1038/s41586-023-06589-1

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