Soon after the Earth coalesced in the
early solar system, it was hit by another planet,
Theia. The collision formed the moon, but
researchers are still trying to piece together
exactly what happened, including what happened to
Theia. For years, researchers have thought that
Theia might have smashed into Earth at an angle,
strong enough to obliterate Theia into little bits
and create the moon. But that might not be the case.
Instead, a recent study suggests that Earth might
actually be a chimera of the two planets.
that instead of a simple sideswipe that crushed
Theia into smaller pieces that formed the moon, the
impact was more of a head-on collision that was so
forceful that it thoroughly mixed Theia and the
Earth together, giving both Earth and the newly
formed moon a unified geological signature.
The 'giant impact hypothesis' has been
floating around since the 1970's, but researchers
are still arguing over the exact nature of the
collision. Unfortunately, there are no instant
replay cameras that date back to that moment in
time, so researchers have to content themselves with
the next best thing: rocks.
By analyzing rocks from both the Earth
and the moon, the researchers found that there was
essentially no difference between their oxygen
isotopes, indicating the possibility that Theia and
the Earth mixed together. The findingdirectly
contradicts results from another
paper in 2014 which found evidence that the moon had
a distinct isotopic signature, supporting the
"We don’t see any difference between
the Earth’s and the moon’s oxygen isotopes; they’re
indistinguishable,” Edward Young, lead author of the
new study said
Why care about the difference between
oxygen isotopes on the Earth and the moon?
Scientists have long been puzzled by the idea that
the Earth and the Moon had very similar geological
signatures. The 2014 finding provided researchers
with an explanation that fit into the computer
models of an oblique collision. If Theia impacted
the early Earth at an angle, scientists would expect
the Moon to be more like Theia, and the Earth...
more like Earth.
A study last year found that it was
possible for Theia to
be almost a twin to Earth which makes
the weird similarity between the geology of the
Earth and moon fit with the sideswipe theory. But
this new theory is simpler, suggesting that instead
of bouncing off each other like pool balls, Theia
and Earth got mixed together like cake batter,
spinning off the moon (made of the same mixture) in
Researchers will continue to try to
reconstruct the planetary collision in the future,
and there will probably be a lot more conversation
and controversy within the planetary geology
community before a consensus is reached.
meantime, it's pretty amazing that Earth withstood
an impact that completely totaled another planet,
and got a moon in the process. Well done, Earth.