Lunar crystals reveal moon is 40M years older than we thought: study

Lifestyle

By Alex Mitchell

That’s one giant leap into the past.

A recent analysis of lunar dirt brought back by the final Apollo mission in 1972 has confirmed that Earth’s satellite is 4.46 billion years old — some 40 million years more than originally thought.

It’s now thought that our moon began as the giant shard of a Mars-sized object that collided with Earth, and never left our obit, according to researchers from The Field Museum of Chicago.

While the parent object that broke up to form the moon would be much older, scientists were able to determine just when the rocky shrapnel became our moon by peering into the lifecycle of lunar crystals.

“These crystals are the oldest known solids that formed after the giant impact,” said senior study author Philipp Heck. “And because we know how old these crystals are, they serve as an anchor for the lunar chronology.”

The Apollo 17 samples indicated that when the object rammed into Earth — and inadvertently formed our moon — thermal, molten energy behind the collision melted the rock, forming what is now the dusty lunar surface.

“When the surface was molten like that … any crystals on the moon’s surface must have formed after this lunar magma ocean cooled,” Heck explained. “Otherwise, they would have been melted and their chemical signatures would be erased.”

Zircon crystals from the moon were analyzed atom-by-atom in a process called radiometric dating at Northwestern University, where radioactive decay was measured between original parent atoms and the new, daughter isotopes that formed after the collision.

It’s “a little bit like an hourglass,” says Heck.

“Radiometric dating works similarly by counting the number of parent atoms and the number of daughter atoms they have transformed to. The passage of time can then be calculated because the transformation rate is known.”

The samples revealed the moon’s minimum age to be 4.46 billion years. Heck emphasized the importance of their findings.

“The moon is an important partner in our planetary system — 40 million years older than we thought: study it stabilizes the Earth’s rotational axis, it’s the reason there are 24 hours in a day, it’s the reason we have tides,” he said.

“Without the moon, life on Earth would look different. It’s a part of our natural system that we want to better understand, and our study provides a tiny puzzle piece in that whole picture.”