By Victoria Allen Science Editor of the Daily Mail
12:00 23 October 2023, updated 12:00 23 October 2023
- Scientists have analyzed moon crystals obtained from the recent Apollo mission
- Their analysis indicates that the Moon is at least 4.46 billion years old
Despite being Earth’s closest celestial companion, there has long been doubt about how and when the Moon formed.
Now there is evidence that the moon is 40 million years older than scientists previously thought.
The most widely accepted explanation for why the Moon exists is the “giant impact theory,” which suggests that a planet the size of Mars collided with Earth.
It is believed that the debris resulting from the collision reunited to form the Moon.
Now, moon crystals brought back from the last Apollo mission in 1972 have been used to estimate the exact age of the moon.
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Researchers say the crystals must have formed after the giant impact that created the Moon, because this high-energy collision melted the rocks that eventually became the Moon’s surface — creating a magma ocean that would have also melted any crystals.
Assuming that the zircon crystals came later, scientists used radiometric dating, looking at the rate of decay of the crystal atoms, to determine their age.
Their results pushed the Moon’s age by 40 million years, to at least 4.46 billion years.
Senior author Professor Philip Hick, from the University of Chicago, explained why knowing the moon’s age is important, saying: “The moon is an important partner in our planetary system – it stabilizes the Earth’s axis of rotation, it’s the reason there are 24 hours in a day, it’s the reason for the tides.
“If it were not for the moon, life on Earth would be different.
“It’s a part of our natural system that we want to understand better, and our study provides a small puzzle piece in that whole picture.”
More than four billion years ago, when the Moon is thought to have formed, our solar system was still young and the Earth was still growing.
To calculate the moon’s age, scientists used a sample of lunar dust brought back by Apollo 17 astronauts from the last manned mission to the moon in 1972.
The dust contains tiny crystals that formed billions of years ago.
Professor Heck said: “These crystals are the oldest known solids that formed after a giant impact.”
“And because we know the age of these crystals, they serve as an anchor for lunar chronology.”
A previous study had suggested the age of the crystals, but it was necessary to take a ‘nano’ look at the samples to fully understand them.
Scientists used a method called atom probe tomography, which works like a “pencil sharpener” to narrow down the lunar sample to a precise point, before using an ultraviolet laser to vaporize atoms from the surface of that point.
Atoms travel through a mass spectrometer, where their speed indicates how heavy they are, and thus their composition.
An atom-by-atom analysis showed how many atoms inside zircon crystals had undergone radioactive decay, which can turn uranium into lead, for example.
By looking at the ratio of different uranium and lead atoms, called isotopes, scientists can tell the age of a sample.
The lead isotope ratio found indicates that the sample was about 4.46 billion years old, so the Moon must be at least that old.
“It’s amazing to be able to get evidence,” said Dr. Jenica Greer, lead author of the study, published in the journal Geochemical Perspectives Letters, who conducted the study when she was at the University of Chicago, but is now at the University of Glasgow. The rock it holds is the oldest part of the moon we have found so far.
“It is a connecting point for many questions about the Earth.” When you know the age of something, you can better understand what happened to it in its history.
Scientists do not agree on how the Moon formed, but many of them believe that it was the result of a collision between Earth and another planet
Many researchers believe that the Moon was formed after a planet the size of Mars collided with the Earth billions of years ago.
This is called the giant impact hypothesis.
The theory suggests that the Moon consists of debris left by our planet’s collision with an object about 4.5 billion years ago.
The colliding object is sometimes called Theia, after the mythical Greek Titan who was the mother of Selene, the moon goddess.
But one mystery still remains, revealed by rocks brought back from the Moon by Apollo astronauts: Why are the Moon and Earth so similar in composition?
Several different theories have emerged over the years to explain the similar fingerprints of the Earth and the Moon.
The impact probably created a huge cloud of debris that completely mixed with the Earth and later condensed to form the Moon.
Or it is possible that Theia is, by chance, chemically similar to a young Earth.
A third possibility is that the Moon formed from terrestrial materials, not from Theia, although this would be an unusual type of impact.
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