The Moon Is 40 Million Years Older Than Scientists Thought

The history and formation of the moon has puzzled astronomers for centuries. Now, researchers have shown that our planet's largest satellite is 40 million years older than previously thought, helping us more precisely pinpoint the geological chronology of the moon's origins.

"The formation date of the Moon is important as only after that Earth became a habitable planet that could sustain life until today," Phillipp Heck, a Professor at the University of Chicago, Curator at the Field Museum and senior author on this study, told Newsweek.

"The Moon helps stabilize the Earth's rotation axis. The lunar tides on Earth and the Moon's light have influences on Earth's systems including its oceans and biosphere. The Moon is the reason why our day currently has 24 hours. The Moon is also an inspiration to humans which is reflected in our culture heritage. Better understanding when (and how) the Moon formed and evolved is a fascinating topic to me."

Today, the most widely accepted theory for the formation of the moon is that, more than 4 billion years ago, a giant Mars-sized object crashed into the Earth, causing it to splinter. The largest of these fragments become the cratered white ball in the sky we see today. However, precisely when this happens remains a mystery.

Using moon crystals brought back from the 1972 Apollo missions, Heck and his team were able to more specifically pinpoint the elusive chronology of the Moon's formation. "These crystals are the oldest known solids that formed after the giant impact," Heck said. "And because we know how old these crystals are, they serve as an anchor for the lunar chronology."

These tiny crystals—which are property of NASA—were found in samples of lunar dust and contain the elements zircon, silicon and oxygen. "Zircon crystals are common in crustal rocks on Earth, the Moon, Mars, and differentiated asteroids, such as Vesta," Heck said. "They are found in igneous rocks such as granite. Zircons are very hard and tough and survive the breakdown of rocks during weathering. Therefore, we can find them in sediments such as sands, and sedimentary rocks such as sandstone. When zircons form, they readily incorporate uranium into their crystals but not lead. Thus, almost all lead in the zircons is from the decay of uranium. This property, together with their durability is what makes them so great for dating rocks."

By studying the crystals atom-by-atom, the team were able to determine how many atoms inside the crystals had undergone this process of radioactive decay. By knowing roughly how long it takes for this decay to take place, this analysis can be used to accurately date the crystals' formation. "Our atom probe analysis concluded the study and leaves no doubt about the 4.46-billion-year age of the zircon," Heck said. "I was very happy to see that with our new study the old age of the zircon crystals could be nailed down without a doubt. I was surprised that everything worked out so neatly."

Heck said that this study—published in the journal Geochemical Perspectives Letters on October 23—goes to show why collecting samples from otherworldly destinations can benefit generations into the future. "I love the fact that this study was done on a sample that was collected and brought to Earth 51 years ago in 1972," Heck said. "At that time atom probe tomography wasn't developed yet and scientists wouldn't have imagined the types of analyses we do today. This is the power of sample return and curation: we can collect a sample, and curate it for decades or more so future generations can address scientific questions with the latest cutting-edge instruments."