In 1932, scientists surveying the S-Egyptian desert came upon pieces of a translucent, pale yellow-green, glassy substance, from tiny fragments to football-sized chunks, scattered over a huge area at the Libyan border. Known as Libyan desert glass,this almost pure silica contained isotopes showing it to be of extraterrestrial origin. But scientists haven't been able to figure out where it came from. Now Farouk El-Baz from Boston Univ. for Remote Sensing, believes the mystery has been solved. Poring over satellite images of the Sahara Desert, he found a gigantic impact crater in the area. At a diameter of 30km, it's "the largest crater yet found in the Sahara," El-Baz says, & big enough to be the source of the glass, which covers a 60x100km area. He believes the crater hadn't been recognized before because it is so big; also, parts of its rims were eroded by two ancient river systems. El-Baz has named the crater, located on the Gilf Kebir plateau, the Kebira. "This is a large crater and well worth scientific investigation," says Friedrich Horz, a crater expert at the Johnson Space Center in Houston, Texas.
