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An international team of scientists has discovered in the Atacama Desert a well-preserved mine of stony meteorites that has allowed it to reconstruct the rate of meteorite falls over the last two million years.
Meteorite with thin and dark melting crust in the Atacama Desert, Chile. Image credit: Jérôme Gattacceca, CEREGE.
"Our goal was to see how the flow of meteorites on the Earth changed on a large scale – millions of years, consistent with astronomical phenomena," said Dr. Alexis Drouard, a researcher at the Aix University -Marseille in France.
To find a record of meteorites over millions of years, Dr. Drouard and his colleagues headed to the Atacama Desert.
"We needed a study site that would preserve a wide range of terrestrial ages where meteorites could persist for long periods of time," said Dr. Drouard.
"While Antarctica and the 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 more than half a million years old."
"Meteorites disappear naturally because of weathering processes (wind erosion, for example), but since these sites are themselves young, the meteorites found on the surface are also young."
"The Atacama Desert is very old – more than 10 million years old. It is also home to the world's largest collection of meteorites. "
The researchers collected 388 meteorites and focused on 54 stony samples from the El Médano region in the Atacama Desert.
Using cosmogenic age dating, they found that the average age was 710,000 years old.
In addition, 30% of the samples were over one million years old and two samples had more than two million.
The 54 meteorites were ordinary chondrites, or stony meteorites containing granular minerals, but covered three different types.
"We were expecting more young meteorites than old ones (because the old ones are lost through aging)," said Dr Drouard.
"But it has turned out that the age distribution is perfectly explained by a constant accumulation of meteorites for millions of years."
"This is the oldest collection of meteorites on the surface of the Earth."
"This harvest of terrestrial meteorites in the Atacama Desert may encourage more research on the study of meteorite flows over long periods of time."
"We found that the meteorite flow appears to have remained constant in number over a period of two million years (222 meteorites greater than 10 g per square kilometer per million years), but not in composition. "
The team's paper was published in the journal Geology.
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A. Drouard et al. The flow of meteorites from the past 2 m.y. recorded in the Atacama desert. Geology, published online May 22, 2019; doi: 10.1130 / G45831.1
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