An international team of scientists has found a wealth of well-preserved stony meteorites in the Atacama Desert that allowed them to reconstruct the rate of falling meteorites over the past two million years.
“Our purpose was to see how the meteorite flux to Earth changed over large timescales — millions of years, consistent with astronomical phenomena,” said Dr. Alexis Drouard, a researcher with the Aix-Marseille Université, France.
To recover a meteorite record for millions of years, Dr. Drouard and colleagues headed to the Atacama Desert.
“We needed a study site that would preserve a wide range of terrestrial ages where the meteorites could persist over long time scales,” Dr. Drouard said.
“While Antarctica and hot deserts both host a large percentage of meteorites on Earth (about 64% and 30%, respectively).”
“Meteorites found in hot deserts or Antarctica are rarely older than half a million years.”
“Meteorites naturally disappear because of weathering processes (e.g., erosion by wind), but because these locations themselves are young, the meteorites found on the surface are also young.”
“The Atacama Desert is very old — over 10 million years. It also hosts the densest collection of meteorites in the world.”
The researchers collected 388 meteorites and focused on 54 stony samples from the El Médano area in the Atacama Desert.
Using cosmogenic age dating, they found that the mean age was 710,000 years old.
In addition, 30% of the samples were older than one million years, and two samples were older than two million.
All 54 meteorites were ordinary chondrites, or stony meteorites that contain grainy minerals, but spanned three different types.
“We were expecting more young meteorites than old ones (as the old ones are lost to weathering),” Dr. Drouard said.
“But it turned out that the age distribution is perfectly explained by a constant accumulation of meteorites for millions years.”
“This is the oldest meteorite collection on Earth’s surface.”
“This terrestrial crop of meteorites in the Atacama Desert can foster more research on studying meteorite fluxes over large time scales.”
“We found that the meteorite flux seems to have remained constant over two-million-year period in numbers (222 meteorites larger than 10 g per squared kilometer per million year), but not in composition.”
The team’s paper was published in the journal Geology.
A. Drouard et al. The meteorite flux of the past 2 m.y. recorded in the Atacama Desert. Geology, published online may 22, 2019; doi: 10.1130/G45831.1