A giant collision between the ancient protoplanet Theia and the proto-Earth about 4.5 billion years ago may have formed Earth’s Moon as well as two continent-sized regions — formally known as large low-velocity provinces — within Earth’s mantle, according to a research team led by Caltech scientists.
In the 1980s, scientists discovered two continent-sized blobs of unusual material deep near the center of the Earth: one beneath the African continent and one beneath the Pacific Ocean.
Each blob is twice the size of the Moon and likely composed of different proportions of elements than the mantle surrounding it.
Where did these strange blobs — formally known as large low-velocity provinces (LLVPs) — come from?
“Terrestrial planet formation concludes with a number of giant impacts among Moon- and Mars-sized planetary embryos,” said Caltech researcher Qian Yuan and colleagues.
“The well-studied giant-impact scenario involves a protoplanet, Theia, colliding with proto-Earth.”
In the study, the authors used computer simulations to propose an explanation for LLVPs.
The material in these regions has been suggested to be between 2.0 and 3.5% denser than the surrounding mantle.
The simulations show that LLVPs may represent buried relics of Theia mantle material that was preserved in proto-Earth’s mantle after the Moon-forming giant impact.
These Theia relics are proposed to have been tens of kilometers across, and the authors suggest that they sunk to the lower region of the mantle and accumulated to form dense blobs above the Earth’s core.
“A logical consequence of the idea that the LLVPs are remnants of Theia is that they are very ancient,” said Dr. Paul Asimow, also of Caltech.
“It makes sense, therefore, to investigate next what consequences they had for Earth’s earliest evolution, such as the onset of subduction before conditions were suitable for modern-style plate tectonics, the formation of the first continents, and the origin of…
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