Studying Rate Of Falling Meteorites Over The Past 2 Millenia
Meteorites bombard Earth every year, but the rate of incoming space rocks changes over time. The discovery of the meteorite collection in Atacama offers researchers opportunity to reconstruct the rate of falling meteorites over the past 2 million years.
"Our purpose in this work was to see how the meteorite flux to Earth changed over large timescales -- millions of years, consistent with astronomical phenomena," said Alexis Drouard, from Aix-Marseille Université, who is part of the team that reported the discovery in a study published in the journal Geology on May 22.
Meteorites naturally disappear because of weathering processes such as the erosion of the wind. To find a meteorite record for millions of years, the researchers needed a site where meteorites are able to persist for a very long time.
Well-Preserved Meteorite Collection Found In Atacama Desert
Antarctica and hot deserts host a large chunk of meteorites on Earth, but because these locations are relatively young, the meteorites found on their surfaces are also young, rarely older than half a million years.
The researchers decided to head to the Atacama Desert in Chile because at over 10 million years, the site is very old.
The researchers collected 388 meteorites and focused on 54 samples from Atacama Desert's El Médano area. Cosmogenic age dating revealed that the average age of the space rocks was 710,000 years old.
Drouard and colleagues also found that 30 percent of the samples were older than 1 million years, and two samples were even older than 2 million years.
"We were expecting more 'young' meteorites than 'old' ones (as the old ones are lost to weathering)," Drouard said. "But it turned out that the age distribution is perfectly explained by a constant accumulation of meteorites for millions years."
Oldest Meteorite Collection
The researchers said that this is the oldest meteorite collection so far found on the Earth's surface.
"With an average age of 710 ka, this collection is the oldest collection of nonfossil meteorites at Earth's surface. This allows both determination of the average meteorite flux intensity over the past 2 m.y," the researchers wrote in their study.