A recent study has extended the estimated age of the Moon to at least 4.46 billion years, which is 40 million years older than previously believed. This research, published in the journal Geochemical Perspectives Letters, aimed to uncover the precise age of the Moon by analyzing lunar samples brought back to Earth by Apollo astronauts in 1972.
The Moon’s origin is closely linked to a cataclysmic event over four billion years ago during the early stages of our solar system. A collision between a Mars-sized object and Earth led to the formation of the Moon, with the largest fragment becoming our celestial companion. Despite this theory, the exact timing of this collision has remained a mystery.
To pinpoint the age of the Moon’s formation, the researchers turned to tiny crystals found within the lunar samples. These crystals, referred to as zircon crystals, are among the oldest known solid materials that developed after the monumental impact. Their age served as a crucial reference point for establishing a lunar chronology.
Philipp Heck, a professor at the University of Chicago and the senior author of the study, explained, “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.”
The researchers utilized a groundbreaking analytical technique called atom probe tomography, which allowed them to accurately date the lunar crystal. By studying the decay of atoms within the zircon crystals, they could determine their age. When certain atoms, like uranium, undergo radioactive decay, they transform into different elements, such as lead. By examining the ratio of these isotopes, scientists can ascertain the age of the crystal.
Jennika Greer, the lead author of the study and a research associate at the University of Glasgow, UK, described the process: “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.”
This method allowed scientists to determine that the zircon crystals on the Moon’s surface must have formed after the lunar magma ocean had cooled, as the extreme heat during the initial impact would have melted any existing crystals. Consequently, these findings provide valuable insights into the Moon’s early history and the formation of our nearest celestial neighbor.
