First evidence of a comet striking earth

The first ever evidence of a comet entering Earth’s atmosphere and exploding, raining down a shock wave of fire that obliterated every life form in its path, has been discovered by a team of South African scientists and international collaborators.

The discovery has provided the first definite proof of a comet striking Earth millions of years ago, and could also help scientists unlock the secrets of the formation of our solar system.

“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 been found on Earth,” said Professor David Block of the University of the Witwatersrand, or Wits University.

The comet entered Earth’s atmosphere above Egypt about 28 million years ago. As it entered the atmosphere, it exploded and heated the sand beneath it to a temperature of 2,000 degrees Celsius. This resulted in the formation of a huge amount of yellow silica glass, which now lies scattered over a 6,000 square kilometre area in the Sahara. A magnificent specimen of the glass, polished by ancient jewellers, was found in Tutankhamun's brooch with its striking yellow-brown scarab.

The research, to be published in Earth and Planetary Science Letters, was conducted by a collaboration of geoscientists, physicists and astronomers including Block, lead author Professor Jan Kramers of the University of Johannesburg, Dr Marco Andreoli of the South African Nuclear Energy Corporation, and Professor Chris Harris of the University of Cape Town.

At the centre of the research was a mysterious black pebble found years earlier by an Egyptian geologist in the area of the silica glass. After conducting chemical analyses on this pebble, the authors concluded that it represented the first known specimen of a comet nucleus, rather than simply an unusual type of meteorite.

The impact of the explosion also produced microscopic diamonds and Kramers explains that diamonds are produced from carbon bearing material, normally formed deep in the earth where the pressure is high. But they could also be generated by very high pressure with shock.

“Part of the comet impacted and the shock of the impact produced the diamonds,” Kramers says.

The team dubbed the diamond-bearing pebble ‘Hypatia’, in honour of the first well-known female mathematician, astronomer and philosopher, Hypatia of Alexandria.

The scientists said comet material was “very elusive” and comet fragments had not been found on Earth before except as microscopic-sized dust particles in the upper atmosphere and some carbon-rich dust in the Antarctic ice.

Space agencies had spent billions to secure the smallest amounts of pristine comet matter to bring it back to Earth. But now the scientists had a radical new approach to studying the material, without spending vast sums.