Around 28 million years ago a comet entered the Earth's atmosphere over Egypt and then exploded. A team of scientists from the University of the Witwatersrand found a small black pebble filled with diamonds.

"Comets always visit our skies – they're these dirty snowballs of ice mixed with dust – but never before in history has material from a comet ever been found on Earth," said Professor David Block of Wits University.

The pebble was found in an area of fused glass and a laboratory analysis showed the rock was very unusual indeed. The scientists found that interspersed with the material of millions of tiny diamonds. These are usually found on Earth in rocks that have been subjected to very high pressures, but the scientists posit that the same materials could be generated in an exploding comet.

"NASA and ESA (European Space Agency) spend billions of dollars collecting a few micrograms of comet material and bringing it back to Earth, and now we've got a radical new approach of studying this material, without spending billions of dollars collecting it,"

The pebble, called "Hypatia" after the first recorded female mathematician Hypatia of Alexandria, is the first direct proof of such extraterrestrial material raining down on Earth.