In 1972, US astronauts Harrison Schmitt and Eugene Cernan collected 243 pounds (110.4 kg) of soil and rock samples for examination on Earth during Apollo 17, the last moon landing.
After 50 years, Schmitt’s zircon crystals in a coarse-grained igneous rock fragment are helping scientists understand the moon’s genesis and age.
According to crystal examinations, the moon formed more than 4.46 billion years ago, 110 million years after the solar system’s formation, scientists announced Monday.
The dominant theory for moon origin is that, during the solar system’s turbulent early history, Mars-sized Theia collided with primordial Earth.
The Apollo 17 crew found a satellite formed 40 meters earlier than believed in lunar rock.
Magma was blasted into space, forming a debris disk that orbited Earth and became the moon. But the moon’s creation time is hard to determine.
When magma cooled and hardened, mineral crystals formed. Atom probe tomography was used to confirm the age of the oldest known solids created following the big impact, the zircon crystals inside Schmitt’s norite fragment.
“I love that this study used a sample brought to Earth 51 years ago. According to cosmochemist Philipp Heck, senior director of research at the Field Museum in Chicago, University of Chicago professor, and senior author of the Geochemical Perspectives Letters study, atom probe tomography wasn’t yet developed, so scientists couldn’t have imagined the types of analyses we do today.
Zircon crystals are the oldest minerals on Earth, Mars, and the moon. UCLA planetary scientist and study co-author Bidong Zhang said zircon lasts forever.
Rock with zircon was obtained in the Taurus-Littrow valley near the southeastern edge of Mare Serenitatis (Sea of Serenity) and housed at NASA’s Johnson Space Center in Houston.
“Zircons are very hard and tough and survive rock breakdown during weathering,” Heck remarked.
Zhang’s study from 2021 used ion microprobe analysis to find out how many uranium and lead atoms were in the crystals and figure out how old the zircon was by counting how fast the radioactive uranium broke down into lead.
If zircon crystal flaws occurred, lead atoms might be involved, so another method was required to verify that age.
The current study employed atom probe tomography to establish the crystals’ age by finding no lead atom problems. “This research underscores the remarkable power of nanoscale or even atomic-level investigations in providing insights into broader, overarching questions,” commented Jennika Greer, a cosmochemist from the University of Glasgow and lead author of the study.