It may not have been the one that killed off the dinosaurs, but a massive comet soared into Earth's atmosphere about 28 million years ago and exploded upon entry, raining down a "shockwave of fire" that killed off everything in its path and created a sea of silica glass spread out over a 6,000 square kilometer area in the Sahara desert.
This discovery marks the first ever definitive proof of a comet striking Earth, says a team of South African scientists and international collaborators that plans to announce its findings Thursday.
"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 in a press release from the University of the Witwatersrand in Johannesburg, South Africa.
Understanding comets and how their impacts affect planets in the earlier stages of formation can help scientists in piecing together answers to longstanding mysteries surrounding our solar system.
The discovery was made after years of chemical analyses were conducted on a black pebble that was found by an Egyptian geologist among the shards of silica left by the comet's blast. The blast had heated the sand beneath it to about 2,000 degrees Celsius when it impacted with Earth. The sea of silica was a well-known area of study as its glass was found in highly valuable jewelry, including a brooch of the Egyptian pharaoh Tutankhamun.
It turns out the black pebble was in fact the comet's nucleus, and the first well-known hand specimen of such an object ever found on Earth. Traditionally, such objects are simply unusual types of meteorites, the scientists explained.
"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," said lead author Jan Kramers of the University of Johannesburg.
The scientists have chosen to name the discovery-bearing pebble Hypatia, after the Alexandrine philosopher and astronomer who became the first well-documented woman in mathematics.
The research is slated to be published in Earth and Planetary Science Letters and includes the work of geoscientists, physicists, and astronomers from the University of Wits, the South African Nuclear Energy Corporation, and the University of Cape Town.