DIAMONDS provide the most lasting evidence of ancient asteroid impacts,
according to geologists in Germany.
Falko Langenhorst of the University of Bayreuth and his colleagues have shown
that the heat and pressure of an impact convert bits of buried coal or graphite
into diamonds (Geology, vol 27, p 747). 鈥淭he shape of impact diamonds
is the same as for the precursor graphite,鈥� says Langenhorst. Researchers had
thought diamonds around impact sites condensed from vapour. The gems survive
after other traces of the collisions have eroded.