Why are most meteorites chondrites?
Most meteorites are chondrites because unmelted, chondritic asteroids are abundant in the parts of the asteroid belt that feed material to Earth, and recent studies trace many falls to a few young asteroid families. Differentiated bodies, whose cores and crusts produce irons and achondrites, supply much less.
About 85 per cent of the meteorites seen to fall are chondrites, and around 80 per cent are ordinary chondrites of the H, L and LL groups. Several factors combine to produce that dominance. The first is what is out there. Many asteroids formed a little later than the earliest bodies, after much of the heat-producing aluminium-26 had decayed, so they never melted. They stayed as chondritic rubble. Melted, layered asteroids certainly existed, and their metal cores give us iron meteorites, but metal cores and basaltic crusts form only small fractions of such bodies.
The second is location. Fragments reach Earth most easily from regions near orbital resonances with Jupiter, especially in the inner asteroid belt. Common asteroids there, the stony S-types, long looked spectroscopically different from ordinary chondrites. Japan's Hayabusa mission settled the question in 2010 by returning grains from asteroid Itokawa that match LL chondrites, showing that the difference was due to space weathering of the asteroid's surface.
The third is recent collisions. Studies published in 2024 traced most ordinary chondrite falls to break-ups of a few asteroid families within the last tens of millions of years, including the Karin family and a young cluster within the Koronis family for H chondrites, and the Massalia family for L chondrites. Fresh collisions create swarms of small fragments that are delivered efficiently to Earth.
Finally, survival matters. Fragile carbonaceous chondrites are more likely to disintegrate in the atmosphere, so even though such material is abundant in space, fewer large stones of it reach the ground. Among the finest dust arriving on Earth, carbonaceous-like material is much more common than among meteorites, a reminder that the meteorites in our collections are a biased sample of what is out there.