Scientists have looked at zircons within lunar samples taken by the Apollo 14 mission, and have estimated that our satellite formed just 60 million years after the birth of the Solar System, which is significantly earlier than previously thought.
According to the new study, published in the journal Science Advances, the Moon’s crust had already solidified 4.51 billion years ago, making our satellite almost a contemporary of Earth. Our natural satellite formed after the primordial Earth was hit by a planetary body the size of Mars, sending material into orbit that eventually coalesced into the Moon. This is known as the Giant Impact hypothesis.
Producing an exact estimate of the Moon’s age is crucial in understanding how rocky planets formed in the Solar System. Earth cannot be fully comprehended without a deep understating of our satellite, and its formation directly or indirectly tells us about the other planets.
“The age of the Moon is indeed critical. The major reason I would give is for our understanding of the Early Earth and when it started to evolve to the habitable planet we know," lead author Dr Mélanie Barboni told IFLScience.
"If we believe that the Moon was formed by one giant impact (or several smaller impacts during a short period), then whatever the proto-Earth looked like before was wiped out by the impact. Our age places the impact really early, which allows a hospitable Earth to develop much earlier as well. That actually fits much better what we have recently learned about the Early Earth."
To date the Moon, the researchers used the ratio of uranium to lead in zircon fragments that were found by NASA’s mission. Over billions of years, uranium radioactively decays into lead, so by measuring the ratio, scientists can estimate how long it’s been since they settled. The researchers also looked at the isotopic ratio of hafnium to double-check their findings.
This estimation is consistent with another study that puts the formation of the Moon at 68 million years after the dawn of the Solar System, though there is still a significant uncertainty around this new value as there is also evidence the Moon could have formed during the first 120 million years. But it is still older than previous estimates that place the birth of our satellite between 150 to 200 million years after the Solar System began.
“It is also important to say that because of plate tectonics, most of the early records have been erased on Earth,” Barboni added. “Other planets such as Venus are still out of reach. Mars might be sampled one day, but it will take time. The Moon is, therefore, our most accessible and preserved record of the first steps of the early Earth and Solar System evolution.”