Moon may be 100 million years younger than previously thought

There may not seem to be much difference between 4.56 billion years and 4.45 billion years, but it's enough to reshape our understanding of the moon, which may be about 100 million years younger than previously thought.

The prevailing theory of the moon's formation holds that planet the size of Mars or larger slammed into Earth about 4.56 billion years ago, shortly after the formation of the solar system. Debris from the impact was thrown from Earth and coalesced to form the moon.

But new analysis of lunar rocks suggest the moon was actually formed between 4.4 and 4.45 billion years ago.

"There are several important implications of this late moon formation that have not yet been worked out," Richard Carlson, of the Carnegie Institution for Science in Washington, D.C., said in a statement.

Carlson is presenting his findings in London Monday at a Royal Society meeting titled "Origins of the Moon."

"For example, if the Earth was already differentiated prior to the giant impact, would the impact have blown off the primordial atmosphere that formed from this earlier epoch of Earth history?" added Carlson.

Scientists know the solar system is 4.568 billion years old. They can also determine the age of smaller bodies such as asteroids with a fair degree of precision by analyzing when these objects went through periods of extensive melting, indicating the collision of smaller bodies known as "planetesimals."

The moon is believed to have had a global ocean of molten rock shortly after its violent formation. Currently, the most precisely determined age for the lunar rocks that formed from that ocean is 4.360 billion years, the researchers said.

But on Earth, scientists have found signs of a major melting event in several locations, dating to 4.45 billion years ago, building evidence that the moon's formation event occurred some 100 million years later than previously believed.