Scientists at UCLA have discovered that Earth is made up of two planets: Earth and Theia.
Theia, a Mars-sized protoplanet, crashed
into Earth 4.5 billion years ago when Earth was just 100 million
Previously, the giant impact hypothesis suggested that
Theia sideswiped Earth, knocking off a chunk.
That chunk, the theory
goes, became the moon. Theia then continued on its journey through
However, this new research, published in the journal Science,
suggests that when Theia collided with Earth, it hit head on and
fused with Earth instead of continuing its trek through the stars.
That means that Theia is still here, under our feet. It's a part of
The study, which was funded by NASA, the Deep Carbon Observatory
and a grant from the European Research Council, focused on comparing
moon rocks to Earth matter.
The findings led the research team to the
conclusion that Earth and the moon are so similar because the moon
was created at the same time that Theia impacted and altered Earth.
Richard Young, head researcher and professor of geochemistry and
cosmochemistry, says that after the impact, "Theia was
thoroughly mixed into both the Earth and the moon, and evenly
dispersed between them."
The identical nature of moon and Earth
matter has long confounded scientists in understanding the
relationship between the two planetary bodies.
To try and get a firm
grasp on the expected differences, Young and his team compared seven
moon rocks (brought back by the Apollo 12, 15 and 17 missions) to
five Earth rocks.
The terrestrial rocks were gathered from Earth's
mantle in Hawaii and Arizona. According to UCLA, "Young's
research team used state-of-the-art technology and techniques to make
extraordinarily precise and careful measurements, and verified them
with UCLA’s new mass spectrometer."
By studying the chemical signatures
of the rocks' oxygen atoms, Young and his team were able to determine
that the moon and Earth-as-we-now-know-it did, in fact, result from
the same event: Theia's collision and fusion with Earth.
elaborates, "This explains why we don't see a different
signature of Theia in the moon versus Earth."
The head-on collision also raises questions about the origin of
water on Earth.
Young suggests that water could have been present
before Theia's impact, or it could have been brought to Earth by
water-rich asteroid impacts millions of years later.
that, "Collisions of growing bodies occurred very frequently
Young points out that Mars seems to have escaped any
such impacts — as far as we know.
Young also offers insight into the planet that could have been.
Had Theia not collided and fused with Earth, it might have evolved
from a planetary embryo into a true planet.
However, we should be thankful that 4.5 billion years ago Theia undertook its crash
Without it, we would not have the moon, and life as we know
it would not exist.