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Each year, millions of meteors intersect with Earth.
Most of these burn up on entering our atmosphere, but some larger space rocks survive the journey and land on Earth’s surface.
These ages are very consistent because the meteorites had to form before the accretion of our planet, and the Earth had to cool down before the first minerals could crystallise.
The Solar System was formed around 4.6 billion years ago, out of the collapse of a dense cloud composed of dusts and gases.
Most meteorites are difficult to distinguish from terrestrial rocks without detailed scientific analysis.
Meteorites are usually covered with a dark, pitted crust resulting from their fiery passage through the atmosphere.
To find evidence of older meteorites in a stable environment, Drouard and his colleagues turned to a collection of over 300 meteorites found in Chile’s Atacama Desert.
“We wanted to see how the meteorite flux to Earth changed over longer timescales, over millions of years,” says Drouard.The compositions of processed meteorites are similar to the crusts, mantles or cores of the terrestrial planets.Thus, they must be fragments of larger asteroids whose interiors melted so that the heavier metals sank to the center and the lighter rocks rose to the surface.A new study looking at a sampling of more than 300 meteorites collected in Chile’s Atacama Desert is shedding some light on the rate and variety of meteor strikes over the past 2 million years.
Meteorites can land anywhere on Earth, but those that fall in deserts and on ice sheets are more likely to be preserved and recovered, says Alexis Drouard, an astrophysicist at Aix-Marseille University in France and lead author of the new study, published in .Radioactive dating shows them to be about 4.6 billion years old, meaning that they have remained essentially unchanged since they first accreted in the solar nebula. They are pieces of rock that accreted in the solar nebula and orbited the Sun for billions of years before finally falling to Earth.