A team of South African scientists writing in the journal ‘Earth and Planetary Science Letters’ said that they have found the first evidence of a comet striking Earth 28 million years ago.
“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 David Block, a member of the research team and a professor of the University of the Witwatersrand.
The researchers said that the comet shot into Earth’s atmosphere and blew up above what is now known as Egypt with blast that wiped out every living thing in its path.
As the fireball exploded it created a super-hot shock wave that heated the sand on the surface to about 2,000 degrees Celsius. The extreme heat and pressure formed a great quantity of yellow silica glass that was spread throughout a 6,000 square kilometer area of the Sahara that’s known as the Libyan Desert Glass strewn field.
A remarkable example of Libyan Desert Glass can be found on an ancient brooch of the Pharaoh Tutankhamun (King Tut) who ruled Egypt from 1332 BC to 1323 BC. Egyptian jewelers polished and carved a piece of the yellow silica to form the body of a scarab that is prominently featured on the brooch.
The first evidence of a comet strike, said the scientists, came in the form of a mysterious 30 gram black pebble that had been found in 1996 by an Egyptian geologist who had been exploring the strewn field.
The pebble now called the Hypatia stone, was named in honor of Hypatia of Alexandria, the first well-known female mathematician, astronomer and philosopher. The researchers said that the stone, which they described as being black, angular, shiny, incredibly hard and extremely fractured, is covered with microscopic diamonds that were created by the shock of the comet’s impact.
“Diamonds are produced from carbon bearing material. Normally they form deep in the earth, where the pressure is high, but you can also generate very high pressure with shock. Part of the comet impacted and the shock of the impact produced the diamonds,” said lead author Professor Jan Kramers of the University of Johannesburg.
After the South African team conducted a number of tests on the Hypatia stone, they concluded that the black pebble was not just an unusual type of meteorite but instead represented the very first known hand specimen of a comet nucleus.
The researchers said that comet material on Earth is incredibly rare. The only other comet fragments that had been found were microscopic dust particles found in the upper atmosphere and in some carbon-rich dust found in Antarctic ice.
“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,” says Kramers.
The South African researchers said that an international collaborative research program has been formed to continue studies of the Hypatia stone.
“Comets contain the very secrets to unlocking the formation of our solar system and this discovery gives us an unprecedented opportunity to study comet material first hand,” said Block.