Apollo 17 Sample Offers Fresh Insights into Moon's Age
In a surprising revelation, moon samples retrieved by Apollo 17 astronauts in the 1970s suggest that the moon might be approximately 40 million years older than we initially thought.
NASA's Eugene Cernan and Harrison Schmitt journeyed to the moon on December 11, 1972, and gathered various samples from its surface. When recently analyzed, these samples were found to contain zircon crystals that are an astounding 4.46 billion years old. Prior research estimated the moon, believed to have been birthed from a grand cosmic collision, to be about 4.425 billion years old.
The study, offering these insights, made its appearance in the journal Geochemical Perspectives Letters recently.
Philipp Heck, the senior researcher of the study and a curator at the Field Museum of Natural History in Chicago, stated, “These crystals are the oldest known solids that formed after the giant impact. And because we know how old these crystals are, they serve as an anchor for the lunar chronology.”
Our solar system's inception was a tumultuous time, with celestial bodies frequently colliding. According to the team of researchers, a body, roughly Mars-sized, struck Earth over 4 billion years ago, resulting in the formation of the moon. However, zeroing in on the exact timing of this monumental event has been a challenge for scientists.
Heck further elaborated, “When the surface was molten like that, zircon crystals couldn’t form and survive. So any crystals on the Moon’s surface must have formed after this lunar magma ocean cooled.”
Advanced Atomic Analysis Sheds Light
Earlier work by Bidong Zhang, from the University of California, Los Angeles, proposed that deducing the crystals' age might yield clues about the moon's precise age.
Zhang, in collaboration with Audrey Bouvier, Heck, and lead researcher Jennika Greer from the University of Glasgow, employed an innovative technique to study these crystals and ascertain the moon's age. For the first time, they turned to atom probe tomography, with the analysis being conducted at Northwestern University in Evanston, Illinois.
Explaining the process, Greer said, “In atom probe tomography, we start by sharpening a piece of the lunar sample into a very sharp tip, using a focused ion beam microscope, almost like a very fancy pencil sharpener. Then, we use UV lasers to evaporate atoms from the surface of that tip. The atoms travel through a mass spectrometer, and how fast they move tells us how heavy they are, which in turn tells us what they’re made of.”
The team managed to determine how uranium atoms within the zircon crystals decayed over time. Heck used an analogy to explain the process: “Radiometric dating works a little bit like an hourglass. In an hourglass, sand flows from one glass bulb to another, with the passage of time indicated by the accumulation of sand in the lower bulb. Radiometric dating works similarly by counting the number of parent atoms and the number of daughter atoms they have transformed to. The passage of time can then be calculated because the transformation rate is known.”
Discovering the Moon's Ancient Secret
Utilizing the lead isotopes in the lunar sample, the team confirmed the crystals' age at 4.46 billion years. Greer expressed, “It’s amazing being able to have proof that the rock you’re holding is the oldest bit of the Moon we’ve found so far. It’s an anchor point for so many questions about the Earth. When you know how old something is, you can better understand what has happened to it in its history.”
Despite having these samples for over five decades, only recent technological advancements have facilitated such detailed analyses. This has led NASA to unveil previously sealed samples from the Apollo era, capitalizing on these new techniques.
To conclude, Heck highlighted the moon's importance: “The Moon is an important partner in our planetary system. It stabilizes the Earth’s rotational axis, it’s the reason there are 24 hours in a day, it’s the reason we have tides. Without the Moon, life on Earth would look different. It’s a part of our natural system that we want to better understand, and our study provides a tiny puzzle piece in that whole picture.”