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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 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 found zircon crystals and gave it an age of 4.46 billion years. Previous estimates put the Moon’s age at 4.425 billion years, formed by a massive celestial collision.
The results were published Monday in the journal Cartas de Perspectivas Geoquimicas.
“These crystals are the oldest known solids that formed after a giant impact. Because we know how old these crystals are,” study senior author Philip Heck and Robert A. Pritzker, curator in the Department of Meteorite and Polar Studies at the Field Museum of Natural History in Chicago, said in a report. It serves as an anchor for lunar chronology.” An announcement.
In the early days of our solar system – when Earth was still forming and growing in size – clumsy and rocky objects often collided in space. Around that time, 4 billion years ago, a Mars-sized object hit Earth, ejecting a large portion of the moon, according to researchers. But scholars have struggled to pinpoint the exact date of this momentous event.
The energy from the collision of a Mars-sized object with Earth melted the rocks that would form the surface of the Moon.
“When the surface was melted like this, zircon crystals could not form and survive,” said Heck, who is senior director of the museum’s Negaunee Integrative Research Center and a professor in the university’s Department of Geophysical Sciences. of Chicago.” formed when the moon’s magma ocean cooled.”
“Otherwise, they would have melted and their chemical signature would have been 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 dating crystals in lunar dust could reveal the moon’s true age. good
Zhang and her colleague Audrey Bouvier, a professor of experimental planetary science at the University of Bayreuth in Germany, approached Heck, a research associate in geology at the University of Glasgow, and Jenica Greer, the study’s lead author, to look at the crystals at the nanoscale. Using advanced techniques. Determining its chemical composition and determining the moon’s age.
Jenica Greer/Northwest University
A particle of lunar zircon is visible under the microscope.
The research represents the first use of an analytical method to date crystals using atomic probe tomography and was conducted with equipment at Northwestern University in Evanston, Illinois, according to the study authors.
“In atom probe tomography, we use a focused ion beam microscope like a very sophisticated pencil sharpener to sharpen a piece of lunar sample to a very sharp point,” said Greer, who was a doctoral candidate at the Field Museum. . And when I worked on the study, the University of Chicago. “We use an ultraviolet laser to vaporize the surface atoms at that tip. Atoms travel through the mass spectrometer and how fast they spin tells us how heavy they are, which in turn tells us what those atoms are made of.”
The analysis showed the number of uranium atoms in the zircon crystals subjected to radioactive decay. Elements can change if their atoms have an unstable configuration of protons and neutrons, causing some of them to decay, in the same way that uranium decays to lead. By tracking how long this process takes, scientists can determine an object’s age by comparing the ratio of uranium to lead atoms.
“Radiometric dating works like an hourglass,” Heck said. “In an hourglass, sand flows from one glass bulb to another glass bulb, showing accumulation of sand in the lower bulb over time. Radioactive dating works in a similar way, counting the number of parent atoms and the number of daughter atoms they replace. Then time can be passed because the rate of change is known.
The research team used lead isotopes found in lunar dust samples to determine that the crystals were 4.46 billion years old, suggesting the moon must be at least that old.
“It’s incredible to have evidence that the rock in it is the oldest part of the moon,” Greer said. “It is a connecting point for many questions about Earth. When you know how old something is, you can better understand what happened to it in its history.”
Dieter Isheim/Northwestern University
The study’s lead author, Jenica Greer, a research associate in geosciences at the University of Glasgow, works at Northwestern University’s Atomic Probe Tomography Center in Evanston, Illinois.
Although lunar samples were returned to Earth more than 50 years ago, it took a long time to develop the technology necessary to analyze the crystals in such detail. That’s why NASA waited until recent years to find some of the original samples collected during the Apollo era, using the most advanced methods to learn more about our planet’s natural moons.
“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 there are tides. If there was no moon, life on earth would be different. This is the part of our natural system that we want to understand better, and our study provides a small piece of the puzzle of that whole picture.
