The moon could have originated from earth, according to a new finding.

Researchers from the University of Chicago have discovered that the moon has some chemical compositions similar to those found on earth. They believe that the moon was born when a Mars-size object named Theia hit the earth 4.5 billion years ago.

At the time both the earth and Theia were still partially molten, the impact causing Theia's core to sink into the earth's core, while lighter ejecta and debris were thrown into space eventually coalescing to form the moon, according to Discovery News.

"The moon was spun out of earth's mantle early on, when the planet's centrifugal force might have exceeded its gravitational force," Nature journal quoted Junjun Zhang at the University of Chicago, as saying.

Researchers discovered this when they were analysing moon rocks gathered by the Apollo missions in the 1970s. They found that the moon rock contains an abundance of titanium-50 and titanium-47 which is usually found on earth. The lunar ratio of the two isotopes was very much similar to that found in earth's mantle.

"But we need to refine current theories that don't explain the incredible similarities of isotopic ratios between the earth and the moon," Discovery quoted Brad Carter, planetary scientist at the University of Southern Queensland, as saying.