The moon is older than scientists thought
A UCLA-led research team reports that the moon is at least 4.51 billion years old, or 40 million to 140 million years older than scientists previously thought.
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 Melanie Barboni, the study's lead author and a research geochemist in UCLA's Department of Earth, Planetary and Space Sciences.
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.
|Astronaut Alan B. Shepard Jr. on the moon in 1971 with the Apollo 14 mission |
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 eight 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, and a co-author of the study. "They are the best mineral in preserving geological history and revealing where they originated."
|Zircon extracted from lunar breccia 14304 collected during the Apollo 14 mission|
[Credit: Melanie Barboni]
"Melanie 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."
The UCLA researchers are continuing to study zircons brought back by the Apollo astronauts to study the early history of the moon.
Author: Stuart Wolper | Source: University of California - Los Angeles [January 12, 2017]