Researchers have discovered evidence of the world that crashed into Earth billions of years ago to form the Moon.
Studies conducted on a lunar rock, brought back by Apollo astronauts, shows signs of the "planet" called Theia.
Researchers claim the discovery confirms the theory that the moon was created by a cataclysmic collision, according to a recent study.
"We can now be reasonably sure that the giant collision took place," Daniel Herwartz, a geochemist at the University of Cologne in Germany and the study's lead author, said in a statement, according to the Christian Science Monitor.
A study on the discovery was published in the journal Science.
The collision occurred some 4.5 billion years ago, according to ScienceMag.org.
While the collision destroyed Theia, much of its remnants, along with some debris from Earth, eventually came together and led to the formation of the moon.
The findings will likely help scientists better understand the moon's origin.
The accepted theory since the 1980s is that the Moon appeared as a result of a collision between the Earth and Theia some 4.5 billion years ago.
Theia was named after a goddess in Greek mythology who was said to be the mother of Selene, goddess of the Moon.
Previous studies showed that the Moon rock originated from the Earth wheres computer simulations showed that the Moon mostly derived from Theia.
"It was getting to the stage where some people were suggesting that the collision had not taken place," Herwartz said to BBC News. "But we have now discovered small differences between the Earth and the Moon. This confirms the giant impact hypothesis."
Professor Alex Halliday of Oxford University, is among many scientists who were shocked that the difference between the Theian material found in the Moon rock and the Earth is so tiny.
"What you are looking for is a much bigger difference, because that is what the rest of the Solar System looks like based on meteorite measurements," Halliday said, according to BBC News.
The computer models that recreated the giant galactic clash indicated that the moon should have a higher portion of Theia in its composition, and a different isotope ratio than that of the Earth, according to ScienceMag.org.
Researchers who studied the Apollo moon rocks previously failed to find any noteworthy difference in isotope ratios between the moon and Earth.
Herwartz and his colleagues used a new approach to look for differences in the ratio of two oxygen isotopes -- oxygen-17 and oxygen-16 -- between moon rocks and Earth rocks.
The researchers were able to extract oxygen samples from all the moon rock samples and discovered that for every million oxygen-16 isotopes, the moon rocks had a dozen more oxygen-17 isotopes than rocks derived from Earth's mantle, according to ScienceMag.org.
This difference "supports the view that the Moon formed by a giant collision of the proto-Earth with (an impactor)," the scientists said in a statement.