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


Geologist and astronaut Harrison Schmidt used an adjustable sampling scoop to recover lunar samples during the Apollo 17 mission in 1972.

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

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 revealed zircon crystals and dated its age to 4.46 billion years. Previous estimates indicate that the age of the Moon, which was formed as a result of a massive celestial collision, is 4.425 billion years.

The results were published Monday in the journal Geochemical Perspectives Letters.

“These crystals are the oldest known solids that formed after a giant impact. Because we know the age of these crystals,” Philip Heck, the study’s senior author, and Robert A. Pritzker, curator of the Department of Meteorites and Polar Studies at the Field Museum of Natural History in Chicago, said in a report. It serves as an anchor for the lunar chronology.” A statement.

The early days of our solar system – when Earth was still forming and growing in size – were chaotic, and rocky objects often collided in space. During that period more than 4 billion years ago, a Mars-sized object collided with Earth, ejecting a large piece of rock that became the moon, according to the researchers. But scholars have struggled to precisely date this pivotal event.

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The energy from the collision of a Mars-sized object with Earth melted the rocks that would eventually form the Moon’s surface.

“When the surface was molten in this way, the zircon crystals were not able to form and survive,” said Heck, who is also senior director of the museum’s Negaunee Integrative Research Center and a professor in the Department of Geophysical Sciences at the University of Chicago. “It was formed after the lunar magma ocean cooled.”

“Otherwise, they would have melted and their chemical signature would be erased.”

Previous research by study co-author Bidong Zhang, a research associate in the Department of Earth, Planetary and Space Sciences at the University of California, Los Angeles, suggested that determining the age of crystals within lunar dust may reveal the actual age of the Moon, well.

Zhang and his colleague Audrey Bouvier, a professor of experimental planetary science at the University of Bayreuth in Germany, approached Heck and lead study author Jennika Greer, a research associate in geosciences at the University of Glasgow, to take a nanoscale look at the crystals using an advanced technique. To determine its chemical composition and determine the age of the moon.

Jenica Greer/Northwestern University

A lunar zircon grain appears under a microscope.

This research represents the first use of the analytical method to date crystals using atomic probe tomography, and was conducted using instruments at Northwestern University in Evanston, Illinois, according to the study authors.

“In atomic probe tomography, we start by sharpening a piece of the lunar sample to a very sharp tip, using a focused ion beam microscope, almost like a very fancy pencil sharpener,” said Greer, who was a doctoral candidate at the Field Museum. and the University of Chicago when I worked on the study. “Then we use ultraviolet lasers to vaporize 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 those atoms are made of.”

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The analysis showed the number of uranium atoms present inside the zircon crystals that had been subjected to radioactive decay. Elements can transform if their atoms have an unstable configuration of protons and neutrons, causing some of them to decay, like how uranium decays to become lead. By tracking how long this process takes, scientists can determine the age of something by comparing the ratio of uranium to lead atoms.

“Radiometric dating works a bit like an hourglass,” Heck said. “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. Radioactive dating works similarly by counting the number of parent atoms and the number of daughter atoms they have transformed into. The passage of time can then be calculated because The rate of transformation is known.

The research team used lead isotopes found in the lunar dust sample to determine that the crystals were 4.46 billion years old, indicating that the Moon must be at least that old.

“It’s amazing to be able to get evidence that the rock it holds is the oldest part of the moon we’ve discovered yet,” Greer said. “It’s a connecting point for many questions about the Earth. When you know the age of something, you can better understand what happened to it in its history.”

Although lunar samples were returned to Earth more than 50 years ago, it took a long time to develop the technology needed to perform such detailed analysis of crystals. That’s why NASA waited Uncover some pristine specimens They were collected during the Apollo era until recent years, allowing further insights into our planet’s natural moon using the most advanced methods.

“The moon is an important partner in our planetary system,” Heck said. “It stabilizes the Earth’s axis of rotation, which is why there are 24 hours in a day, and why we have tides. If it weren’t for the Moon, life on Earth would be different. It’s part of our natural system that we want to understand better, and our study provides a small puzzle piece in That whole picture.

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