Researchers have discovered evidence that 28 million years ago a comet entered Earth's atmosphere over Egypt and exploded, killing all life forms in its path.
The explosion sent a shock wave of fire down over the Sahara desert, the South African researchers say. This heated the sand to 2,000 C and resulted in the formation of yellow silica glass, which was used by ancient jewelers, and microscopic diamonds.
The key to the research was a black pebble found by an Egyptian geologist. After thorough analysis, the researchers determined it was the first known specimen of a comet nucleus.
"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," David Block of Wits University in Johannesburg said in a release.
The research will be published in Earth and Planetary Science Letters.