The moon is 40 million years older than thought

More than 4 billion years ago, when the solar system was young and Earth formed, a giant object the size of Mars collided with our planet. Over time, the remnants of that collision collided and formed a natural satellite, the Moon.

Until now, scientists haven’t been able to pinpoint exactly when this happened, but according to the details of a new study published this week in the journal Geochemical Perspectives Letters, the moon is at least 4.46 billion years old. about 40 million years more than thought.

The researchers used crystals brought from Month Apollo astronauts in 1972 to calculate the time of the Moon’s formation.

“These crystals are the oldest known solids that formed after the giant impact. And because we know how old they are, they serve as an anchor for the moon’s chronology,” says Philipp Heck, professor from the University of Chicago and lead author of the study.

The discovery was the result of a collaboration between Heck and the study’s lead author, Jennika Greer, while she was preparing her PhD at the Field Museum and the University of Chicago.

Crystals in lunar dust

Moon dust samples contain tiny crystals that formed billions of years ago and contain clues to when the Moon was formed.

When a Mars-sized object collided with Earth to form the Moon, the energy from the impact melted the rock and became the surface of the moon.

“When the surface was this molten, zircon crystals could not form and survive. So the crystals on the moon’s surface had to form after this lunar magma ocean cooled, or they would have melted.” and their chemical signatures would disappear,” says Heck.

Since the crystals must have formed after cooling magma ocean, Determining the age of zircon crystals would reveal the minimum possible age of the Moon.

Previous research had suggested this age, but today’s study determined the moon crystal’s exact age thanks to an analytical method called atomic tomography.

This atom-by-atom analysis showed how many atoms within the zircon crystal underwent radioactive decay.

When an atom has an unstable configuration of protons and neutrons in its nucleus, it undergoes disintegration, releasing some of those protons and neutrons and turning them into elements. different (e.g. uranium decays into lead).

Scientists have determined the time it takes for this process to occur, and by looking at the ratio of different atoms of uranium and lead (called isotopes) present in a sample, they can determine its age.

The lead isotope ratio the researchers found indicates that the sample is about 4.46 billion years old, so the Moon must be at least that old.

Knowing when the Moon was formed is important because “it is an important partner in our planetary system: it stabilizes the Earth’s axis of rotation, it is the reason why there are 24 hours in a day, it is the reason why we have tides. Life on Earth without the Moon It would be different. “It’s a part of our natural system that we want to understand better, and our study adds a small piece of the puzzle to that whole picture,” concludes Heck.