[Rockhounds] A remnant of a protoplanet may be hiding inside Earth

[Kreigh Tomaszewski]

A protoplanet slammed into the Earth about 4.5 billion years ago, knocking
loose a chunk of rock that would later become the *moon*
<https://www.livescience.com/earths-moon.html>. Now, scientists say that
remnants of that protoplanet can still be found, lodged deep inside
Earth, *Science
Magazine reported*
<https://www.sciencemag.org/news/2021/03/remains-impact-created-moon-may-lie-deep-within-earth>
.

If remains of the protoplanet, known as Theia, did stick around after the
impact, that may explain why two continent-size blobs of hot rock now lie
in the *Earth* <https://www.livescience.com/19102-amazing-facts-earth.html>'s
mantle, one beneath Africa and the other under the Pacific Ocean. These
massive blobs would stand about 100 times taller than Mount Everest, were
they ever hauled up to Earth's surface, *Live Science previously reported*
<https://www.livescience.com/core-mantle-ulvz-blobs-enormous.html>.

Theia's impact both formed the moon and transformed Earth's surface into a
roiling magma ocean, and some scientists theorize that the blobs formed as
that ocean cooled and crystalized, Science reported. Others think the blobs
contain Earth rocks that somehow escaped the effects of the collision and
nestled, undisturbed for millions of years, near the planet's center.

But last week, at the *Lunar and Planetary Science Conference*
<https://www.hou.usra.edu/meetings/lpsc2021/pdf/1980.pdf>, Qian Yuan, a
doctoral student in geodynamics at Arizona State University (ASU) Tempe,
presented an alternate hypothesis.

He proposed that, after the *moon-forming impact*
<https://www.space.com/19275-moon-formation.html>, dense material from
Theia’s mantle descended deep beneath the Earth's surface, accumulating
into what we now know as "the blobs." According to Yuan's models, rocks
1.5% to 3.5% denser than Earth's mantle would not mix into the surrounding
rock. Rather, they would sink to the bottom of the mantle, near the inner
core.

https://www.livescience.com/theia-may-be-in-mysterious-mantle-blobs.html