Study: Huge blobs in Earth's mantle might be relics from moon-forming collision

An international team of scientists from China and the U.S. has made a remarkable discovery, suggesting that two massive objects buried in the Earth's deep mantle could be relics from the moon's formation about 4.5 billion years ago.

A leading theory holds that the moon formed when a Mars-sized planet dubbed Theia struck Gaia or the early Earth, and the collision flung the top layer of the Earth into space, where the debris recombined to form the moon.

The researchers from California Institute of Technology, Arizona State University and Shanghai Astronomical Observatory (SHAO) under the Chinese Academy of Sciences have provided new evidence for this hypothesis in a study published on Thursday in the journal Nature.

They proposed that two continent-sized anomalies with low seismic velocities in the lowermost mantle, beneath the African continent and the Pacific Ocean, respectively, might stem from Theia mantle materials (TMMs), which are intrinsically 2 to 3.5 percent denser than proto-Earth's mantle.

Using giant-impact simulations, the team revealed that a fraction of Theia's mantle may have been delivered to and preserved in the proto-Earth's solid lower mantle after the moon-forming giant impact.

They have found that Theia's relics, like moon rocks, are rich in iron, thus making them denser than their surrounding substance.

The dense blobs with a size of tens of kilometers in the aftermath of the impact might later sink and accumulate into thermochemical piles atop Earth's core and survive to the present day to become a natural consequence of the moon-forming giant impact, according to the study.

The results also provide a new perspective for understanding the internal structure of the Earth, the long-term evolution of the Earth, and even the formation process of the inner solar system.

"The moon-forming giant impact appears to be the origin of the early mantle's heterogeneity and marks the starting point for the Earth's geological evolution over the course of 4.5 billion years," said Deng Hongping from SHAO, a co-author of the study.

"Our study may lend clues to the habitability of exoplanets beyond our solar system," Deng added.