The Moon Is 40 Million Years Older Than Thought, Lunar Rock Samples Suggest

In 1972, the Apollo 17 astronauts—the last people to walk on the moon to this day—brought back rocks and soil from the lunar surface. Now, more than 50 years later, scientists are still using these samples to better understand Earth’s natural satellite.

Researchers analyzed crystals in the lunar rocks and found the moon may be older than previously thought, according to a new study published Monday in the journal Geochemical Perspectives Letters. The research pushes its age back by 40 million years, positing that the moon formed just 110 million years after the solar system did.

“This indicates that the moon is at least 4.46 [billion years old], which contradicts some of the recent proposals for a young moon formation,” Romain Tartèse, a planetary scientist at the University of Manchester in England who was not involved in the research but edited the paper, tells the Guardian’s Nicola Davis.

“It moves the goal post. It pushes back the minimum age of the moon formation,” Jennika Greer, first author of the study and a cosmochemist at the University of Glasgow in Scotland, tells the Washington Post’s Carolyn Y. Johnson.

The moon is 40 million years older than we thought, new research led by Dr Jennika Greer (@StjarnaStenar) of @UofGGES, @FieldMuseum and @UChicago reveals.

Read how crystals returned from the Apollo missions helped uncover the moon’s age https://t.co/yZ6jUnA1sR pic.twitter.com/n4I9wZ6GL6

— University of Glasgow (@UofGlasgow) October 23, 2023

Our moon likely formed when a Mars-sized body rammed into Earth around 4.5 billion years ago, according to NASA. This collision left behind a swarm of planetary debris, which coalesced in Earth’s orbit to create the moon. At first, it was covered in a global ocean of magma, but within about 100 million years, the new celestial body cooled down and mostly crystallized.

Exactly when this happened, however, has been a matter of scientific debate. Some studies have suggested the collision that made the moon occurred between 4.52 and 4.47 billion years ago, while others have placed its formation much later, between 4.43 and 4.42 billion years ago, according to the new paper.

In the past, some scientists have tried to pinpoint the age of lunar rocks by analyzing crystals within them, made of a tough mineral called zircon. The zircon crystals contain radioactive uranium, which decays into lead at a reliable rate. As a result, the ratio of lead to uranium can indicate the age of the crystals, according to Nicole Mortillaro of the Canadian Broadcasting Corporation.

A 2021 study looked at zircon crystals in an Apollo 17 rock sample and found they were 4.46 billion years old, give or take 31 million years. But the researchers couldn’t determine whether the lead in the sample was from radioactive decay or had just been there by chance, leading to some uncertainty in their result, writes New Scientist’s Alex Wilkins.

The new study examined the same sample using a different dating method, called atom probe tomography. This technique involves evaporating individual atoms from one of the zircon crystals with a laser beam and identifying them, per the Washington Post. The analysis found that the crystal formed 4.46 billion years ago—40 million years earlier than the previously confirmed oldest crystal found on the moon.

“We now have a date of the zircons, so we can tell the time by which the magma ocean must have been solidified, or largely solidified,” Philipp Heck, a co-author of the study and cosmochemist at the University of Chicago, tells New Scientist. “It essentially anchors the entire lunar chronology. It’s almost like putting a nail into the lunar timeline.”

Still, that doesn’t mean 4.46 billion years is the oldest possible age of the moon.

“I am convinced that there is older stuff on the moon—we just haven’t found it yet,” Heck tells Popular Science’s Laura Baisas. “I even think we have older zircons in the Apollo samples.”

“This study also exemplifies the great benefit of sample return missions and proper curation,” Tartèse tells the Guardian. “More than 50 years after these samples were returned, we are still making key [discoveries] about the moon and the inner solar system as technology continues developing.”

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.