50-year-old rock collected by Apollo 17 astronaut in 1972 reveals moon's age

The results are based on an analysis of these zircon crystals, and they carry significant implications for our understanding of lunar formation.

The leading hypothesis regarding the moon's creation suggests that during the tumultuous early days of our solar system, a Mars-sized object known as Theia collided with a young Earth.

This cataclysmic impact ejected molten rock into space, giving rise to a debris disk that eventually coalesced into the moon. However, pinning down the exact timing of this lunar birth has long been a challenge.

The story unfolds with the cooling and solidification of magma, allowing mineral crystals to take form. In their quest for precision, researchers employed a technique called atom probe tomography to validate the age of the oldest known solids post-impact—those zircon crystals nestled within a fragment of a rock variety termed norite, collected by Schmitt.

Philipp Heck, a senior director of research at the Field Museum in Chicago, a University of Chicago professor and senior author of the study published in the journal Geochemical Perspectives Letters, expressed his fascination, saying, "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 wasn't developed yet, and scientists wouldn't have imagined the types of analyses we do today."

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Highlighting the remarkable resilience of zircon crystals, UCLA planetary scientist Bidong Zhang commented, "Interestingly, all the oldest minerals found on Earth, Mars, and the moon are zircon crystals. Zircon, not diamond, lasts forever."

The rock containing these invaluable zircon crystals was gathered from the Taurus-Littrow valley, situated at the southeastern edge of the lunar Mare Serenitatis (Sea of Serenity), and has been preserved at NASA's Johnson Space Centre in Houston. The durability of zircons has enabled their survival even in the face of terrestrial weathering.

"Zircons are very hard and tough and survive the breakdown of rocks during weathering," Heck said.

In 2021, Zhang led a study utilising ion microprobe analysis to determine the concentration of uranium and lead atoms within these crystals, thus calculating their age based on the radioactive decay of uranium into lead over time.

Due to a potential issue related to lead atom defects within the zircon crystal structure, a separate technique was necessary to validate this age. The latest research used atom probe tomography to confirm that no such complications existed, thereby solidifying the age of the crystals.

Lead author Jennika Greer, a cosmochemist at the University of Glasgow in Scotland, underscored the significance of nanoscale and atomic-level investigations in addressing broader questions. "I see this as a great example of what the nanoscale, or even atomic scale, can tell us about big-picture questions."

The moon, with its average distance from Earth of approximately 239,000 miles (385,000 km) and a diameter of roughly 2,160 miles (3,475 km), represents just over a quarter of Earth's size.

The colossal impact that birthed the moon was a transformative event in Earth's history, altering our planet's rotational speed. Subsequently, the moon played a pivotal role in stabilising Earth's axial tilt and reducing its rotational velocity.

As Heck put it, "The formation date of the moon is important as only after that Earth became a habitable planet."

Zhang added, "The moon helps stabilise Earth's axis for a stable climate. The moon's gravitational pulls help shape the ocean's ecosystem. The moon is inspirational to human cultures and explorations. And NASA and other space agencies see the moon as a steppingstone for future deep-space explorations."