Terrestrial weathering
Terrestrial weathering is the slow breakdown of a meteorite by air, water and temperature changes after it lands on Earth.
Meteorites form in space, where there is no liquid water or oxygen-rich air. Once they reach Earth, our environment begins to attack them. This is terrestrial weathering, meaning weathering on Earth. Iron-nickel metal rusts into iron oxides, the iron sulfide mineral troilite breaks down, and over long times, silicate minerals turn into clays. Water can carry in salts and carbonates that crack the stone from inside, and the dark fusion crust gradually flakes off.
Weathering matters because it changes the meteorite's chemistry and can hide or destroy the scientific clues inside it. That is why freshly fallen meteorites, such as Winchcombe, which fell in England in 2021 and was collected within days, are so valuable. Wet, mild climates destroy meteorites fastest. Cold, dry Antarctica preserves them best, and hot deserts come somewhere in between.
Scientists describe weathering with codes such as W0 to W6. You can recognise it by brown or orange rust stains, especially around metal grains, loss of fusion crust and a crumbly surface. To slow weathering, keep meteorites dry and never wash them in water.
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Level: Explorer Ages 10 and up