The rock was subsequently mixed with other lunar surface materials into one sample.
NASA astronauts who visited the Moon during the Apollo 14 mission hauled back a whole bunch of material from its surface. According to an global team of researchers, the two-gram piece of quartz, feldspar, and zircon was found embedded in a larger rock called Big Bertha.
"The sample also contains quartz, which is an even more unusual find on the moon", Professor Nemchin said. The Earth fragment was likely blasted off our planet by a powerful impact about 4 billion years ago, according to the new research.
Experts found that the moon rock formed at temperatures similar to those found on Earth today.
But one mystery has persisted, revealed by rocks the Apollo astronauts brought back from the moon: Why are the moon and Earth so similar in their composition?
This rock fragment is over 4 billion years old.
Scientists believe that the moon itself was formed around 4.5 billion years ago as a result of a collision between the Earth and another astronomical body approximately the size of Mars.
It's possible that the fragment did indeed form on the Moon, but the conditions for that would be unlike anything we've seen on the satellite.
We're not talking about a "Moon was once part of Earth" rock (that's just one hypothesis for the Moon's origin, anyway).
"The clast was ejected from the Earth during a large impact, entrained in the lunar regolith as a terrestrial meteorite with the evidence of reducing conditions introduced during its incorporation into the Imbrium ejecta and host breccia", the study explains. This impact jettisoned material through Earth's primitive atmosphere, into space, where it collided with the surface of the Moon (which was three times closer to Earth than it is now) about 4 billion years ago.
An worldwide team associated with Center for Lunar Science and Exploration (CLSE) in the USA found evidence that the rock was launched from Earth by a large impacting asteroid or comet. It was then excavated by one or more large impact events and launched into cislunar space. Around that time, the planet was regularly bombarded by cosmic objects of all shapes and sizes, some responsible for producing craters thousands of kilometers in diameter on Earth - so this isn't that far-fetched of an explanation at all.
After the rock came to rest on the lunar surface, another impact 3.9 billion years ago partially melted and buried it, scientists believe. At the time, Earth would have been experiencing asteroid impacts capable of creating craters that were hundreds of miles wide.
Kring expects that some geologists in the scientific community won't accept the finding because it seems controversial.
"It is an extraordinary find that helps paint a better picture of early Earth and the bombardment that modified our planet during the dawn of life", study co-author David Kring, a Universities Space Research Association (USRA) scientist at the Lunar and Planetary Institute in Houston, said in a statement.