Rock brought back by Apollo 17 reveals the age of the Moon – 10/23/2023 – Science

The last time humans set foot on the Moon, during the Apollo 17 mission in 1972, American astronauts Harrison Schmitt and Eugene Cernan collected around 110.4 kg of soil and rock samples that were brought to Earth for further study. .

Half a century later, crystals of the mineral zircon within a fragment of coarse-grained igneous rock collected by Schmitt are providing scientists with a deeper understanding of the formation of the Moon and the exact age of Earth’s celestial partner.

The Moon is about 40 million years older than previously thought, having formed more than 4.46 billion years ago — 110 million years after the birth of the solar system —, scientists said on Monday, with based on crystal analysis.

The leading hypothesis for lunar formation is that during the solar system’s chaotic early history, a Mars-sized object called Theia collided with the early Earth. This launched magma — molten rock — into space, forming a disk of debris that orbited the Earth and coalesced into the Moon. But the exact moment of the Moon’s formation has been difficult to determine.

Mineral crystals were able to form after the magma cooled and solidified. The researchers used a method called atom probe tomography to confirm the age of the oldest known solids that formed after the giant impact, the zircon crystals inside the fragment of a type of rock called norite collected by Schmitt.

“I love the fact that this study was done on a sample that was collected and brought to Earth 51 years ago. At that time, atom probe tomography had not yet been developed and scientists would not have imagined the types of analyzes that we do today,” said cosmochemist Philipp Heck, senior director of research at Chicago’s Field Museum, professor at the University of Chicago and senior author of the study published in the journal Geochemical Perspectives Letters.

“It is interesting to note that all of the oldest minerals found on Earth, Mars and the Moon are zircon crystals. Zircon, not diamond, lasts forever,” added Bidong Zhang, a planetary scientist at UCLA and co-author of the study.

The rock containing the zircon was collected in the Taurus-Littrow Valley, on the southeastern edge of the lunar Mare Serenitatis (Sea of ​​Serenity), and stored at NASA’s Johnson Space Center in Houston (USA).

A study led by Zhang, published in 2021, used a technique called ion microprobe analysis to measure how many uranium and lead atoms were in the crystals, calculating the age of the zircon based on the decay of radioactive uranium into lead over time. This age needed to be confirmed by another method due to a possible complication involving lead atoms if there were defects in the zirconium crystal structure.

The new study used atom probe tomography to determine that there were no complications involving the lead atoms, confirming the age of the crystals.

“The giant impact that formed the Moon was a cataclysmic event for the Earth and changed the Earth’s rotation speed. After that, the Moon had an effect on stabilizing the Earth’s rotation axis and slowing the rotation speed,” he said Heck. “The date of the Moon’s formation is important, as only after that did the Earth become a habitable planet.”