Oldest meteorite collection on Earth found in one of the driest places

Oldest meteorite collection on Earth found in one of the driest places
The L6 ordinary chondrite El Médano 128, a 556 g meteorite recovered in the Atacama Desert. Photo courtesy CCJ-CNRS, P. Groscaux. Credit: Photo courtesy CCJ-CNRS, P. Groscaux.

Earth is bombarded every year by rocky debris, but the rate of incoming meteorites can change over time. Finding enough meteorites scattered on the planet's surface can be challenging, especially if you are interested in reconstructing how frequently they land. Now, researchers have uncovered a wealth of well-preserved meteorites that allowed them to reconstruct the rate of falling meteorites over the past two million years.

"Our purpose in this work was to see how the flux to Earth changed over large timescales—millions of years, consistent with astronomical phenomena," says Alexis Drouard, Aix-Marseille Université, lead author of the new paper in Geology.

To recover a meteorite record for millions of years, the researchers headed to the Atacama Desert. Drouard says they needed a study site that would preserve a wide range of terrestrial ages where the meteorites could persist over long time scales.

While Antarctica and hot deserts both host a large percentage of meteorites on Earth (about 64% and 30%, respectively), Drouard says, "Meteorites found in hot deserts or Antarctica are rarely older than half a million years." He adds that 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 in Chile, is very old ([over] 10 million years)," says Drouard. "It also hosts the densest collection of meteorites in the world."

  • Oldest meteorite collection on Earth found in one of the driest places
    Large meteorite found in the Atacama Desert. Photo by Jérôme Gattacceca (CEREGE). Credit: Jérôme Gattacceca (CEREGE).
  • Oldest meteorite collection on Earth found in one of the driest places
    Meteorite with thin, dark, fusion crust in the Atacama Desert. Photo by Jérôme Gattacceca (CEREGE). Credit: Jérôme Gattacceca (CEREGE).
  • Oldest meteorite collection on Earth found in one of the driest places
    Meteorite recovery campaign in the Atacama Desert (Nov. 2017). Credit: Katherine Joy (University of Manchester).

The team 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)," says Drouard. "But it turned out that the age distribution is perfectly explained by a constant accumulation of meteorites for millions years." The authors note that this is the oldest meteorite collection on Earth's surface.

Drouard says this terrestrial crop of meteorites in the Atacama can foster more research on studying meteorite fluxes over large time scales. "We found that the meteorite flux seems to have remained constant over this [two-million-year] period in numbers (222 meteorites larger than 10 g per squared kilometer per million year), but not in composition," he says. Drouard adds that the team plans to expand their work, measuring more samples and narrowing in on how much time the meteorites spent in space. "This will tell us about the journey of these meteorites from their parent body to Earth's surface."

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More information: The meteorite flux of the past 2 m.y. recorded in the Atacama Desert, Geology, doi.org/10.1130/G45831.1 , pubs.geoscienceworld.org/gsa/g … st-2-m-y-recorded-in
Journal information: Geology

Citation: Oldest meteorite collection on Earth found in one of the driest places (2019, May 23) retrieved 22 September 2019 from https://phys.org/news/2019-05-oldest-meteorite-earth-driest.html
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May 23, 2019
Makes sense that the collection of meteorites survived intact on the Atacama desert.
No native iron-working culture.

I doubt if the surrounding indigenous would have known of the cosmic debris or it's significance.

The Old World, with dromedary camels plus regular supplies of disposable slaves?
Pretty much cleared the Sahara, Sahel & Arabian deserts clean of such deposits.
Probably just a couple of thousand years ago.

Perhaps, magnetic sensors could still find older deeply buried deposits?

I am not sure about similar deposits surviving long-term in wetter climes?

May 23, 2019
In wetter climes it is often hard to find them, unless obviously large and fresh, due to the amount of foliage and ground cover. And, if it is in an area like the Pacific Northwest coastal climes, they Can be found on top of forest duff, but it is rather rare to do so, more often than not they are not found and then weather quickly. Carbonaceous Chondrites and the Nickle/Iron bearing types tend to erode/rust or be dissolved by biological action.

Still, with a sharp eye you CAN find them, it is just a whole lot more difficult.

May 23, 2019
based on crater counts on Earth Mars and the Moon the impact flux has doubled over the past 290 million years.


May 24, 2019
i do not see, how that hypothesis would be proved or disproved.
Until we do some lengthy prospecting on Luna & Mars.

& that time period seems rather short considering the astro-geological history.

What if you consider the last billion years? The period 300+million years ago may gave been a very productive aaon for incoming rock.

Then a deep pause as the number of rocks orbiting in, slowly built up again?

& if you could advance a method to prove there is a population increase?
All the really big rocks. Vulnerable to being diverted out of their regular obits?

& pilled in towards the Sun? Seem to be all used up...
Now & into the foreseeable future, it's all the little crap left over from cthonic collisions that are now cycling in-system.

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