- In 2020, researchers discovered that the moon is actually 85 million years younger than we once thought.
- Computer simulations revealed that the moon formed roughly 4.425 billion years ago.
- How and when the moon formed has long been a point of contention between planetary scientists.
How old is the moon? Much younger than scientists previously thought.
Back in 2020, researchers from the German Aerospace Center and the University of Münster released new estimates for the age of the moon. According to their modeling, it’s 85 million years younger than previous estimates have suggested.
Scientists have long estimated that the moon formed some 4.51 billion years ago, when a Mars-sized object (which we’ve since dubbed Theia) smashed into Earth. At the time, the guts of our newly formed planet were beginning to take shape.
The collision tore away a chunk of Earth’s mantle and flung it into orbit, where it morphed into a massive ring of dust and rock that began to clump together. “From this, the moon was formed in a short time, probably in just a few thousand years,” planetary scientist and study co-author Doris Breuer, of the German Aerospace Center, said in a statement.
In their paper, published in Science Advances, Breuer and her colleagues reveal that this infamous impact occurred around 4.425 billion years ago, give or take about 25 million years. In the aftermath of the impact, the moon looked a lot like Mustafar—a molten marble with a piping hot magma ocean more than 600 miles deep.
The scientists used computer simulations to show exactly how long it would have taken the moon’s magma ocean to solidify, as this would help pinpoint the precise age of the moon. Their models indicated it took a whopping 150–200 million years for that magma to fully crystalize. Previous models have suggested it only took 35 million years for the moon’s hard, rocky exterior to form.
The impact also kickstarted the formation of Earth’s core. Heavier elements like nickel and iron sank toward the planet’s center, while a layer of silicate rock formed the mantle layer around it.
“This is the first time that the age of the moon can be directly linked to an event that occurred at the very end of the Earth’s formation, namely the formation of the core,” planetary scientist Thorsten Kleine, of the University of Münster in Germany, said in the statement.
Over the years, we’ve been able to glean bits and pieces of information from the moon rocks brought back during the Apollo missions and Russia’s Luna missions. It’s been more than 50 years since we first set foot on the lunar surface, and we still have a lot to learn.
Jennifer Leman is a science journalist and senior features editor at Popular Mechanics, Runner's World, and Bicycling. A graduate of the Science Communication Program at UC Santa Cruz, her work has appeared in The Atlantic, Scientific American, Science News and Nature. Her favorite stories illuminate Earth's many wonders and hazards.
