Apollo 17 samples reveal that the moon is 40 million years older than previously thought

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Lunar dust collected by the Apollo 17 astronauts in the 1970s revealed that the moon is 40 million years older than previously believed.

After landing on the moon on December 11, 1972, NASA astronauts Eugene Cernan and Harrison Schmidt collected rocks and dust from the lunar surface. A new analysis of that sample found zircon crystals and dated them to 4.46 billion years old. According to previous estimates, the Moon was formed by a massive celestial collision, 4.425 billion years old.

The findings were published in the journal Monday Geochemical Review Letters.

“These crystals are the oldest known solids that formed after a giant impact. Because we know how old these crystals are, they serve as an anchor for the lunar chronology,” said Philip Heck, Robert A. Pritzker said. Report.

The early days of our solar system — when Earth was still forming and growing in size — were chaotic, with rocky bodies often colliding in space. Around that time, 4 billion years ago, an object the size of Mars slammed into Earth, turning from a large chunk of rock into the Moon, researchers report. But scientists have struggled to precisely date this important event.

The energy of the impact of a Mars-sized object hitting Earth melted the rock that would eventually form the surface of the Moon.

“When the surface was melted like that, zircon crystals could not have formed and survived. So any crystals must have formed on the surface of the moon after this lunar magma ocean cooled,” said Heck, senior director of the museum’s Negaunee Integrated Research Center and a professor in the University of Chicago’s Department of Geophysics.

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“Otherwise, they would have melted and their chemical signatures would have been destroyed.”

Previous research by Bidong Zhang, an assistant researcher in the Department of Earth, Planetary and Space Sciences at the University of California, Los Angeles, had suggested that determining the age of crystals in lunar dust could reveal the moon’s true age. Well done.

Zhang, a professor of experimental planetology at the University of Bayreuth in Germany, and co-author Audrey Bouvier approached Heck, a research associate in geosciences at the University of Glasgow, and lead study author Jenica Greer to look at crystals at the nanoscale using an advanced technique. Determine their chemical composition and state the age of the moon.

The research represents the first application of the analytical method of dating crystals by atomic scanning tomography and was carried out using instruments at Northwestern University in Evanston, Illinois, the study authors report.

“In atomic tomography, we start by sharpening a piece of the lunar sample to a very sharp tip, using a focused ion beam microscope, like a very fancy pencil sharpener,” said Greer, a postdoctoral fellow at the Field Museum. and the University of Chicago when he worked on research. “Then we use UV lasers to vaporize atoms from the surface of that tip. The atoms travel through a mass spectrometer, and that tells us how fast they’re moving and how heavy they are, which tells us what they’re made of.

The analysis shows how many uranium atoms within the zircon crystals experienced radioactive decay. If their atoms have an unstable configuration of protons and neutrons, some of them will decay – similar to how uranium turns into lead. By tracking how long this process takes, scientists can determine the age of something by comparing the ratio of uranium to lead atoms.

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“Radiometric dating works a bit like an hourglass,” Heck said. “In an hourglass, sand flows from one glass bulb to the other, indicating that sand has accumulated in the lower bulb over time. Radiometric dating works similarly by counting the number of parent atoms and the number of daughter atoms they have replaced. Since the transformation rate is known, the passage of time can be calculated.

The research team used lead isotopes within a lunar dust sample to determine that the crystals were 4.46 billion years old, indicating that the moon itself must be at least as old.

“It’s amazing to have evidence that the rock you’re holding is the oldest bit of the moon we’ve ever found,” Greer said. “This is a key point for many questions about Earth. If you know how old something is, you can better understand what happened to it in its history.

Jennica Greer is shown at the Northwestern University Atomic Tomography Center.

Although lunar samples were returned to Earth more than 50 years ago, it took time to develop the technology necessary to conduct detailed analysis of the crystals. That’s why NASA waited until recent years to unseal some of the oldest samples collected during the Apollo era, using more advanced methods to allow more insights into our planet’s natural satellite.

“The Moon is an important player in our planetary system,” Heck said. “It stabilizes the Earth’s spin 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 be different. It’s part of our natural system that we want to understand better, and our study is a small part of that whole picture. Presents the puzzle piece.

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