mdsolar writes in with a story about evidence of a comet explosion over Egypt 28 million years ago. "Saharan glass and a brooch belonging to King Tut provide the first evidence of a comet directly impacting Earth, a new study claims. The finding may help unlock some of the mysteries surrounding the birth of our solar system. About 28 million years ago a comet exploded over Egypt, creating a 3600F (2000C) blast wave that spread out over the desert below. The fiery shockwave melted the sand, forming copious amounts of yellow silica glass scattered over 2,300 square miles (6,000 square kilometers) of the Sahara. Polished into the shape of a scarab beetle, a large piece of this glass found its way into a brooch owned by the famed Egyptian boy king Tutankhamen. 'Because there is no sign of an impact crater, it has been a mystery as to what kind of celestial event actually could have caused this debris field, but a small, black stone found lying in the middle of the glass area caught our attention,' said study co-author David Block, an astronomer at Wits University in Johannesburg, South Africa."