There have been many theories about how the Earth formed. Now, researchers found that the Earth may be made up of two planets that fused together after a violent collision some 4.5 billion years ago.

A group of astronomers from University of California, Los Angeles (UCLA) was investigating how the Moon formed. They found that a small planet collided over the Earth, left it and went on to generate the Moon. But then, they also found evidence that the said planet never really departed from Earth. In fact, it is already part of the planet now.

High-Speed Crash Billions Of Years Back

About 4.5 billion years ago, a planet called Theia powerfully side-swiped the Earth at an angle of 45 degrees or more.

Scientists are aware of that, but they thought it was a high-speed collision only, not exactly a crash.

The new research suggests that the collision was actually very violent that the so-called planetary embryo fused with both the Moon and the Earth.

Studying Moon And Earth Fingerprints

The researchers came up with their findings by analyzing seven rocks obtained from the moon by Apollo missions 12,15 and 17. They also studied volcanic rocks from the mantle of the Earth, which was collected from Hawaii and Arizona.

The main goal of the investigators is to determine the oxygen isotopes of the rocks. Each cosmic body in the Solar system has a unique ratio of oxygen isotopes just like humans have different fingerprints.

The oxygen isotopes enable scientists to determine where a particular planetary body originated.

The team utilized highly-advanced technology and methods to come up with precise measurements. They also verified their findings with the university's new mass spectrometer.

Astonishing Results

The researchers found that there were no discrepancies between the oxygen isotope ratio of the Earth and and Moon, with lead author Edward Young calling it "indistinguishable."

Both Earth and the Moon had a fair share of Theia, says Young.

"This suggests that well-mixed material from the giant impact must have formed both the Moon and Earth's mantle," the researchers wrote.

Young added that this discovery explains why they were not able to see variations in the fingerprints of Theia in the moon and Earth.

Theia may have been a whole different planet if the collision did not occur. Scientists believe that it may be as big as the Earth or as small as Mars.

The study was published in the journal Science on Jan. 29.