The actual age of the Moon is revealed. How old is it?

A new study reveals the Moon could be over 100 million years older than previously believed.

For years, researchers estimated the Moon formed 4.35 billion years ago, following a collision between a Mars-sized object and early Earth.

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However, fresh evidence suggests the Moon’s formation occurred earlier, around 4.51 billion years ago, with a significant “re-melting” event happening later in its history.

What are these new findings?

Research published in Nature challenges the idea that the Moon was formed around 4.35 billion years ago, after a Mars-sized object collided with early Earth. This widely accepted timeline is based on lunar rock samples from NASA’s Apollo missions.

The study suggests the Moon was formed earlier - around 4.51 billion years ago - and underwent a dramatic “re-melting” event, which was previously mistaken as its formation period. This event occurred as the Moon moved away from Earth, with gravitational forces causing extreme heating that reshaped its surface and obscured its true age.

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Francis Nimmo, the study’s lead author and professor at UC Santa Cruz, explained that this heating likely “reset all the clocks” in lunar rocks, which misled earlier age estimates. “The Moon rocks are not telling us when the Moon formed, but they are telling us when a later event happened that heated the Moon,” Nimmo told NBC News.

While debates over the Moon’s age have occurred for decades, this research supports the growing view that its history is more complex than Apollo-era analyses revealed. Nimmo noted that the Apollo findings were reasonable at the time, but planetary formation models have consistently struggled to explain how major impacts could still occur 200 million years after the Solar System’s formation.

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“This has been the state of affairs, with two camps wanting different ages,” Nimmo said.

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‘Tidal heating’

The revised timeline for the Moon’s formation could clarify the long-standing mystery of why zircon minerals in Apollo lunar samples are around 4.5 billion years old. Previously, scientists believed these minerals crystallised during the Moon’s creation, but their age has consistently puzzled researchers.

In their study, Francis Nimmo and his colleagues propose that the intense heating of the Moon’s surface was caused by a phenomenon called “tidal heating.” Nimmo explained that as the Moon moved further from Earth, its orbit became unstable at certain points. During these times, Earth’s gravitational forces stretched and compressed the Moon, generating heat.

A similar process is thought to occur between Jupiter and its moons. For instance, the gravitational forces of the gas giant may heat the interiors of some of its icy moons, with evidence suggesting this could even melt rock into magma on the volcanic Jovian moon, Io.

Nimmo also spoke about the potential of recent and upcoming lunar missions to shed further light on the Moon’s evolution. China’s Chang’e 6 mission recently retrieved samples from the Moon’s far side, marking the first time such material has been collected. Analysis of the soil revealed volcanic rock fragments dating back 4.2 billion and 2.8 billion years, pointing to at least 1.4 billion years of volcanic activity. NASA’s Artemis missions are also expected to contribute insights.

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Carsten Munker, a geologist at the University of Cologne who was not involved in the study, described tidal heating as a plausible explanation for discrepancies in the Moon’s timeline. He said that the new study “was written by people who were long in the camp that the moon was younger, but now all three [authors] agree with an older lunar age.”

“This certainly moves our understanding closer,” Munker said, according to NBC News.

While the difference between 4.35 billion and 4.51 billion years might seem minor on a cosmic scale, understanding what happened during those turbulent early years of the solar system is crucial to uncovering how the planets, including Earth, took shape.

“The evolution of the solar system was quite rapid. Within just a few tens of millions of years, the whole array of celestial bodies as we know them today was formed,” Munker said.

He also discussed the importance of precise timing, stating that a clear timeline of these early events is important for understanding the origins of the Earth-Moon system and, by extension, the dynamics of the entire solar system.

With inputs from agencies