The new research from Katak suggests that the remains of that ancient planet known as Theia are still inside the Earth and explain the origin of the "lumps" near the core-mantle boundary. Other remnants of it coalesced to form the moon
A Caltech-led study suggests that two huge, iron-rich structures deep in the Earth's crust are the remains of Theia, an ancient planet that collided with the Earth, and also created the Moon. This discovery answers long-standing questions about the origin of the Moon and the fate of Theia.
In the 80s, geophysicists discovered two enormous and unusual lumps deep near the center of the Earth, one beneath the African continent and one beneath the Pacific Ocean. Each clump is twice as large as the Moon and probably consists of different proportions of elements compared to the mantle around it.
Where did these strange clumps – large low velocity regions (LLVP) – come from in the first place? A new study led by researchers from Calcutta suggests that they are the remains of an ancient planet that violently collided with Earth billions of years ago in the same giant impact that formed our Moon.
The study, published in the journal 'Nature', also offers an answer to another mystery in planetary science. Researchers have long hypothesized that the Moon was formed by a giant collision between Earth and a smaller planet called Theia, but no trace of Theia has ever been found in the asteroid belt or in meteorites. The new study suggests that most of its material merged into the young Earth, forming the LLVPs, while residual debris from the collision coalesced into the Moon.
The research was led by Qian Yuan, a post-doctoral research fellow at O. Kay. Earl, in the labs of Paul Asimo and Michael Gurnis of Caltech.
Yuan, a geophysicist by training, noticed in 2019 that the moon is relatively rich in iron. Zolotov added that no trace of the impacting body that must have collided with the Earth has yet been found. "Right after Mikhail said that no one knows where the impactor is now, I had a moment of enlightenment and realized that the iron-rich impactor could have turned into lumps in the mantle," says Yuan.
Yuan worked in multidisciplinary collaborations to simulate different scenarios of the chemical composition of Thaya and its collision with Earth. The simulations confirmed that the physics of the collision could have led to both the formation of the LLVP and the Moon. Part of the mantle of Thya could have merged into the Earth's mantle, where it eventually solidified together to form the two lumps recognizable today at the Earth's core-mantle boundary; Other debris from the collision (which contained material from Thya and Earth) mixed together to form the Moon. Given such a powerful collision, why did Thya's material coalesce into two separate clumps instead of mixing together with the rest of the forming Earth? According to the simulations the researchers showed, most of the energy delivered by the Tayya collision remained in the upper half of the mantle, leaving Earth's lower mantle colder than lower-resolution impact models estimated. Because the lower mantle was not completely melted by the impact, the iron-rich lumps of material from it remained largely intact as they sank to the base of the mantle, like the colored masses of wax in an extinguished lava bulb.
The next steps will be to examine how the early presence of non-uniform cellular material deep inside the Earth could have affected its interior processes, such as plate tectonics.
"It makes sense that the LLVP are very ancient relics of Thaya," says Asimo. "Therefore, it makes sense to further investigate what their consequences were for the earliest evolution of the Earth, such as the beginning of subduction before conditions suited modern plate tectonics, the formation of the first continents, and the origin of the earliest minerals on Earth."
The new study answers two long-standing mysteries in planetary science: what are the mysterious giant lumps near the Earth's core, and what happened to the planet that collided with the Earth and created the Moon.
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