The Moon is Older than Scientists thought

This is astronaut Alan B. Shepard Jr. on the moon in 1971 with the Apollo 14 mission. Credit: NASA

Formation occurred 4.51 billion years ago, 40 million to 140 million years older than scientists previously thought A UCLA-led research team analysed minerals from the moon called zircons that were brought back to Earth by the Apollo 14 mission in 1971. The moon’s age has been a hotly debated topic, even though scientists have tried to settle the question over many years and using a wide range of scientific techniques. “We have finally pinned down a minimum age for the moon; it’s time we knew its age and now we do,” said Mélanie Barboni, geochemist in UCLA.

The moon was formed by a violent, head-on collision between the early Earth and a “planetary embryo” called Theia, a UCLA-led team of geochemists and colleagues reported in 2016. The newest research would mean that the moon formed “only” about 60 million years after the birth of the solar system– an important point because it would provide critical information for astronomers and planetary scientists who seek to understand the early evolution of the Earth and our solar system.

That has been a difficult task, Barboni said, because “whatever was there before the giant impact has been erased.” While scientists cannot know what occurred before the collision with Theia, these findings are important because they will help scientists continue to piece together major events that followed it. It’s usually difficult to determine the age of moon rocks because most of them contain a patchwork of fragments of multiple other rocks. But Barboni was able to analyze 8 zircons in pristine condition. Specifically, she examined how the uranium they contained had decayed to lead (in a lab at Princeton University) and how the lutetium they contained had decayed to an element called hafnium (using a mass spectrometer at UCLA). The researchers analyzed those elements together to determine the moon’s age. “Zircons are nature’s best clocks,” said Kevin McKeegan, a UCLA professor of geochemistry and cosmochemistry. “They are the best mineral in preserving geological history and revealing where they originated.”

The Earth’s collision with Theia created a liquefied moon, which then solidified. Scientists believe most of the moon’s surface was covered with magma right after its formation. The uranium-lead measurements reveal when the zircons first appeared in the moon’s initial magma ocean, which later cooled down and formed the moon’s mantle and crust; the lutetium-hafnium measurements reveal when its magma formed, which happened earlier.

Previous studies concluded the moon’s age based on moon rocks that had been contaminated by multiple collisions. McKeegan said those rocks indicated the date of some other events, “but not the age of the moon.” The UCLA researchers are continuing to study zircons brought back by the Apollo astronauts to study the early history of the moon. http://newsroom.ucla.edu/releases/the-moon-is-older-than-scientists-thought-ucla-led-research-team-reports