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The moon is 40 million years older — explained

More than 50 years after astronauts returned the last batch of Apollo-era moon rock, scientists said they had made a finding that would have been impossible in 1972.

That was the year astronaut Eugene Cernan and Harrison Schmitt, the first scientist-astronaut became the last humans — so far — to land on the moon. 

Cernan and Schmitt landed in the Taurus-Littrow valley on the edge of Mare Serenitatis, because it was thought to be a geologically diverse site.

They collected a total of 110.5 kilograms (243.6 pounds) of lunar rock and soil — 741 samples in all. The samples include the three major lunar rock types: basalts, breccias, and highland crustal rocks. 

So how old is the moon?

The new study appeared to show that the moon is about 40 million years older than previously thought.

It now seems to have formed about 4.46 billion years (or "GA" — giga annum) ago — putting its formation within the first 110 million years of the birth of our solar system.

Many lunar samples have been studied over the years, but a good amount has been stored and released to researchers only slowly, because scientists predicted early on that technology would improve over time and enable better insights.

The findings published in Geochemical Perspectives Letters on October 23, 2023,

are themselves based on a new technology called atom probe tomography (APT). 

 

Apollo 17 astronauts Harrison and Cernan collected 110.5 kilograms of lunar rock and soil, some of which is still being investigated more than 50 years later© NASA/REUTERS

"I love the fact that this study was done on a sample that was collected and brought to Earth 51 years ago. At that time, atom probe tomography wasn't developed yet and scientists wouldn't have imagined the types of analyses we do today," Philipp Heck, a senior author of the study, told Reuters.   

How did scientists discover the moon's new age?

The scientists re-analyzed crystals from Lunar Sample 72255, which was known to contain 4.2 billion- year-old zircon — some of the oldest ever found.

Zircon is also the oldest mineral known to exist on Earth and, as such, geologists say, it holds vital information about the formation of our planet and life as we know it.

The scientists in the new study used APT, which has nanoscale spatial resolution, to determine the clustering of lead in the samples. The distribution of lead is commonly used to estimate the age of zircon in rock.

Why is zircon relevant to the age of the moon?

In their study, the researchers write that "the leading hypothesis" for the formation of the Earth–Moon system is the Giant Impact hypothesis. A huge object called Theia, which was possibly the size of Mars, is thought to have collided with Earth as it was forming. That, it's said, caused an ejection of debris that quickly formed into the sphere we call our moon. 

That created what is known as the Lunar Magma Ocean — a theory that, the scientists said, explains the composition of the moon's interior.

There were subsequent bombardments of the moon's surface, which the researchers write "reworked and melted the earliest crust," leaving some zircon modified and other zircon pristine, or preserved.

And it was by spotting the preserved zircon within crystal grains from lunar sample 72255 that they were able to redetermine the moon's age, they said.

"I see this as a great example of what the nanoscale, or even atomic scale, can tell us about big-picture questions," Jennika Greer, co-author of the study, told Reuters.

How old is the moon compared to the Earth?

The Earth is estimated to be between 4.5 and 4.6 billion years old. That makes the moon only a fraction younger at 4.46 billion years old. 

Edited by: Derrick Williams: Author: Zulfikar Abbany: Story by Zulfikar Abbany: DW