Alan B. Shepard Jr. on the Moon in 1971 with the Apollo 14 mission. (Photo : NASA)
A UCLA-led study argues the Moon is 40 million to 140 million years older than scientists think, and that the Moon's formation occurred 4.51 billion years ago or millions of years earlier than previously believed.
The findings are based on an analysis of minerals from the Moon called "zircons" brought back to Earth by the Apollo 14 mission in 1971. They were published Jan. 11 in the journal Science Advances.
The Moon's age has been a hotly debated topic, and scientists have tried to settle the question over many years 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, the study's lead author and a research geochemist in UCLA's Department of Earth, Planetary and Space Sciences.
The accepted theory is the Moon was formed by a violent, head-on collision between the early Earth and a "planetary embryo" called Theia.
The newest research means the Moon formed "only" about 60 million years after the birth of the solar system -- an important point because it provides critical information for astronomers and planetary scientists seeking to understand the early evolution of the Earth and our solar system.
Barboni said this has been a difficult task 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 eight zircons in pristine condition.
Specifically, she examined how the uranium they contained had decayed to lead in a lab at Princeton University. She also determined how the lutetium they contained had decayed to an element called hafnium using a mass spectrometer at UCLA. 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, and a co-author of the study. "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.
"Mélanie was very clever in figuring out the Moon's real age dates back to its pre-history before it solidified, not to its solidification," said Edward Young, a UCLA professor of geochemistry and cosmochemistry and a co-author of the study.
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."
UCLA researchers are continuing to study zircons brought back by the Apollo astronauts to study the early history of the Moon.
