Scientists believe that Earth as we know it is actually composed of two planets which, in the distant past, merged due to a head-on collision that was so violent that it resulted in the formation of our moon.
Prior to this, researchers believed that our Moon was created when a smaller planet referred to as Theia grazed Earth and split up, which resulted in smaller chunks (debris) being sent into space where Earths gravity captured them.
But, if this theory was correct, it would mean that the chemical composition of the moon is different from Earth since our satellite would have been made up mostly of fragments of Theia.
However, after studying moon rock samples brought back by Apollo mission astronauts, scientists from the University of California have discovered that oxygen isotopes are identical to those on Earth.
This suggests that the collision that occurred 4.5 billion years ago between Theia and Earth was so violent that it caused the two planets to meld together forming a new planet, and a chunk of the collision eventually led to the formation of our Moon.
Scientists analyzed seven lunar rocks which were brought back to Earth by the Apollo 12, 15 and 17 missions, and six volcanic rocks of the Earth’s mantle, five from Hawaii and one from Arizona. The study revealed a chemical signature in oxygen atoms which suggest that 99.9% of the oxygen of our planet is O-16, (because each atom has eight protons and eight neutrons).
But scientists also found small amounts of heavier isotopes of oxygen, O-17, which has an extra neutron, and O-18, which has two extra neutrons. Earth, Mars and other planetary bodies in our solar system have a unique relationship of S-17 and S-16, each with a distinctive mark.
Almost two years ago, in 2014, scientists from Germany reported in the Journal Science that our moon has its own unique ratio of oxygen isotopes which differ from those on Earth. However, the new study has found out that this is not the case, changing everything we know about Early Earth and the eventual formation of our moon.
“We don’t see any difference between the Earth’s and the Moon’s oxygen isotopes; they’re indistinguishable,” said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.
“Theia was thoroughly mixed into both the Earth and the Moon, and evenly dispersed between them.
“This explains why we don’t see a different signature of Theia in the Moon versus the Earth.”
Scientists believe that the collision between Theia and Earth occurred roughly one hundred million years after our planet formed.
Theia, the planet that collided with early Earth didn’t survive the huge collision, but its remains make up large parts of Earth and our moon. According to Prof Young, Theia was roughly the same size as Earth, while other experts believe it could have been similar in size to Mars.
The new research was published in the journal Science.