The first evidence of a comet striking Earth occurred 28 million years ago, scientists discovered.

Scientists have uncovered evidence of a 28-million-year-old comet, which exploded over Egypt, killing all signs of life in its path.

The comet entered the atmosphere over Egypt and exploded, heating the sand to 3,632 degrees Fahrenheit. As a result, a 2,316 square mile area of the Sahara Desert was heated to glass.

The glass, a yellow silica glass, is called Libyan Desert Glass. A scrap of it was found in Tutankhamen's brooch.

Amazingly, despite the size of the sea of glass, a tiny pebble proved evidence of the comet. The black pebble was "angular, black, shiny, extremely hard and intensely fractured." Researchers were trying to prove the pebble, called Hyptia, was part of a comet rather than a meteorite.

The black pebble was found by an Egyptian geologist in the sea of silica glass. Researchers used a host of analyses on the pebble to uncover its origon and prove the pebble belonged to a comet, rather than a meteorite.  Scientists conducted analyses including X-ray diffraction, Raman spectroscopy, and transmission electron microscopy on the pebble-and finally, they realized they were right.

"It's a typical scientific euphoria when you eliminate all other options and come to the realization of what it must be," lead author Jan Kramers, a geology professor at the University of Johannesburg, said in a statement.

The pebble was proven to be a comet because of the diamonds embedded within it. Diamonds are produced from carbon bearing material," Kramers explained. "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."

Meteorites have much less carbon than the pebble's carbon makeup. "If you compare it with meteorites ... they contain only about three percent carbon. And this thing contains 65 percent carbon," Kramers added.

"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 said in a statement. Block is an astronomy professor at Wits University in Johannesburg.

"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," Block said.

Scientists have had difficulty finding comet fragments-thus far, they've turned up some dust particles in Antarctic ice, and that's about it. But because they've had practice identifying Hyptia, more may be found in the future.

"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," Kramers said.