麻豆传媒

Call it extraterrestrial bling. Fossilised sea creatures have been found that coated themselves in tiny diamonds created in the asteroid impact that killed off the dinosaurs.

The fossils were discovered by a team led by Michael Kaminski, a geologist at University College London. They went to the Umbria-Marche basin of eastern Italy in search of the fossilised remains of deep-ocean creatures called agglutinated foraminifera. These amoeba-like single-celled organisms build protective 鈥渢ests鈥� around themselves by sticking together sediment grains from the sea floor. Curiously, they seem to prefer heavy grains, presumably to help them sink to the bottom of the ocean.

Kaminski鈥檚 team looked for fossils in rock samples taken just above and below the sediment layer created by the huge asteroid impact at the end of the Cretaceous period, 65 million years ago. The foraminifera tests they found were mainly composed of common minerals such as quartz, but some of the component grains were unusually rich in metals such as nickel and cobalt, indicating that they had originated in outer space.

Even more surprising were microscopic granules of carbon, no more than 10 micrometres across, which were subsequently identified as diamonds. 鈥淭he foraminifera were deliberately using extraterrestrial diamonds in their shells,鈥� says Kaminski.

The majority of these microdiamonds were formed from terrestrial graphite rock that was altered by the extreme pressure and temperature of the asteroid impact, but a small proportion was truly extraterrestrial, derived from carbon in the asteroid itself.

It seems the main reason the foraminifera chose grains containing diamonds and metals for their tests was the lack of other grains of a similar density at this particular site. What remains a mystery is how these ancient foraminifera were able to pick out the densest grains, an ability they share with their latter-day descendants (pictured).

Kaminski鈥檚 results were published last month in the Proceedings of the Seventh International Workshop on Agglutinated Foraminifera.

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