Moon 100 Million Years Younger Than Thought: Lunar Rock Reveals Truth

How old is our moon? That's a good question. After analyzing a piece of lunar rock brought back to Earth by the Apollo 16 mission in 1972, researchers have discovered that our moon is a lot younger than we first thought.

Our moon first formed when a large planet-like object and proto-Earth collided during the very early evolution of our solar system. This massive impact caused melted material to fly into space, eventually forming a moon that began with a deep liquid magma ocean. As the moon cooled, this magma ocean solidified into different mineral components. The lightest of these minerals floated upward to form the oldest crust. That's why today scientists can examine samples taken from this ancient crust and gain new insights into the formation of the moon.

The researchers examined the isotopes of the elements lead and neodymium in order to place the age of a sample at 4.36 billion years. This, in particular, is a lot younger than previous estimates of the moon's age which ranged to nearly as old as the age of the solar system itself at 4.567 billion years.

"We have analyzed a piece of lunar rock that was brought back to Earth by the Apollo 16 mission in 1972," said James Connelly, one of the researchers, in a news release. "Although the samples have been carefully stored at NASA Johnson Space Center since their return to Earth, we had to extensively pre-clean the samples using a new method to remove terrestrial lead contamination. Once we removed the contamination, we found that this sample is almost 100 million years younger than we expected."

The findings mean that either the moon either solidified significantly later than previous estimates, or the sample itself doesn't represent a crystallization product of the original magma ocean. In fact, the new age suggests that the oldest crust on both Earth and the moon formed at approximately the same time. This, in turn, can reveal a little bit more about how the moon and Earth formed. In fact, the new findings mean that there will need to be major revisions to previous models for the formation of the moon.

"There are several important implications of this late moon formation that have not yet been worked out," said Richard Carlson of the Carnegie Institution for Science in an interview with Discovery News. "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?"

Currently, the scientists are seeking the answers to these questions as they continue to learn more about the moon.

The findings are published in the journal Nature.