Scientists have made strides in understanding the moon's formation, pinpointing its crystallization to 4.43 billion years ago. This discovery stems from an analysis of lunar rocks collected during the Apollo missions, employing advanced techniques to measure rare minerals.
Nicolas Dauphas, a leading researcher and professor at the University of Chicago, stated, "It took us years to develop these techniques, but we got a very precise answer for a question that has been controversial for a long time." The study involved measuring lutetium levels—a radioactive element found in moon rocks—which gradually transforms into hafnium over time. By comparing these proportions with meteorites and other solar system materials, scientists calculated when the moon's KREEP layer formed.
The research supports theories about the solar system's early history. Around 4.57 billion years ago, debris collisions led to planet formations. A significant impact with Earth likely resulted in the moon's creation from resultant debris. Initially, this collision created a molten magma ball around Earth that cooled rapidly by geological standards but remained partially molten due to an insulating mineral crust.
Dauphas noted that once about 80% of the lunar magma ocean solidified, cooling slowed down due to this crust: “It’s like putting on a coat in Chicago when it’s cold out—you will not lose heat as fast.” Understanding how long it took for the moon to become fully solid provides insights into Earth's own history and its transition to habitability.
"This finding aligns nicely with other evidence—it’s a great place to be in as we prepare for more knowledge about the moon from the Chang-e and Artemis missions," said Dauphas.
The study was dedicated by Dauphas in memory of his wife and fellow geochemist Reika Yokochi. He remarked on her contributions: “She was instrumental to all aspects of my research.”
The findings were published under "Completion of lunar magma ocean solidification at 4.43 Ga" by Dauphas et al., funded by NASA.