But only a tiny fraction of the meteorites which fall to earth today are carbonaceous chondrites.

ECONOMIST: Paleoforensic science

It is from a class known as the carbonaceous chondrites - primitive, carbon-rich meteorites that contain organic compounds such as amino acids.

BBC: Rare space rock in British lab

The 44-year-old son of a coal miner made his first million trading coal and coke (of the carbonaceous variety nothing untoward).

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That is a necessary but not a sufficient condition, as the type of rock involved, called carbonaceous chondrite, is found in other asteroids, too.

ECONOMIST: Asteroid impacts

Carbonaceous chondrites contain tiny jewels - presolar diamonds and sapphires.

BBC: Rare space rock in British lab

So, if the next meteorite fragments to turn up in rocks from the end of the Cretaceous are also carbonaceous chondrites, the Case of the Dinosaur Killer can probably be closed.

ECONOMIST: Paleoforensic science

If the arrival was made of carbonaceous chondrite, it would have weighed 25 times as much as all the other carbonaceous chondrite material that had fallen over the previous half million years.

ECONOMIST: Paleoforensic science

Assuming that the figure was similar during the Cretaceous, it would be a long shot that the first fossil meteorite to turn up from 65m years ago was made of such a rock unless a huge extra supply of carbonaceous chondrite had suddenly arrived on the planet.

ECONOMIST: Paleoforensic science