Ancient Planet Could Be Buried Within Earth, Study Finds
A team of scientists at Arizona State University have presented evidence to suggest the remains of an ancient planet may be buried deep in Earth’s mantle.
The collision is thought to have taken place during Earth’s infancy, about 4.5 billion years ago, and for many years scientists have wondered whether remains of the protoplanet may be hidden beneath the surface of the Earth.
Qian Yuan, a PhD student in seismology at Arizona State University (ASU), Tempe, discussed this hypothesis last week at the Lunar and Planetary Science Conference, though Yuan backed up his explanation with new isotopic evidence and modelling.
The theory is based on the fact that two layers of rock the size of a continent sit below West Africa and the Pacific Ocean, apparently straddling the Earth’s core. They are up to 1,000km tall and several times as wide, making them ‘the largest thing in the Earth’s mantle’, according to Yuan.
The mantle makes up 84% of the total volume of the Earth and lies between the core and the crust.
Known as large low-shear velocity provinces (LLSVPs), the two layers of rock slow down seismic waves from earthquakes that pass through them, suggesting they are denser and chemically different from the mantle rock that surrounds them, Science Mag reports.
Based on the evidence and modelling, Yuan believes the LLSVPs are the remains of Theia, commenting: ‘This crazy idea is at least possible.’
Other theories suggest the rocks may have formed from the depths of Earth’s primordial magma ocean, or that they could be puddles of primitive mantle rock that survived Theia’s impact, but seismologist Edward Garnero noted that Yuan’s presentation marks the first time anyone has presented multiple lines of evidence to support the presented theory.
Garnero commented: ‘I think it’s completely viable until someone tells me it’s not.’
Sujoy Mukhopadhyay, a geochemist at the University of California (UC), said evidence indicates the LLSVPs have existed since the time of the collision that caused the creation of the moon.
Seismic imaging has shown that volcanoes on both Iceland and Samoa are fed by plumes of magma that can be traced to the LLSVPs, and over the past decade Mukhopadhyay is among scientists who found lavas on the islands contain an isotopic record of radioactive elements, which formed only during the first 100 million years of Earth’s history.
Astrophysicist Steven Desch, who worked with Yuan on the study, has previously found evidence to suggest Theia was nearly as big as Earth and quite dry; making it a protoplanet that would have separated into layers 2% to 3.5% denser than present-day Earth.
Yuan noted that if Theia’s rocks were up to 3.5% denser than those found in the Earth’s mantle, it would enable ‘the Theia mantle materials to sink to the Earth’s lowermost mantle and accumulate into thermochemical piles that may cause the seismically-observed LLSVPs’.
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