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Uncovered crater solves mystery

Discovery of the Kebira impact crater confirms silica glass strewn over southwestern Egypt formed when a meteor collided with Earth millions of years ago.
Kebira Crater
This color-composite satellite image shows Kebira Crater in Egypt's Western Desert. Kebira's outer rim is 19 miles (31 km) in diameter. The recently discovered crater is almost twice the size of the Aorounga Impact Crater, the Sahara's next largest impact crater.
Boston University Center for Remote Sensing
April 1, 2006
Scientists combing through satellite images of Egypt's Western Desert made a surprising discovery: the largest impact crater found to date in the Sahara. The find confirms what many scientists have suspected for the last 75 years — a meteorite more than half a mile (1.2 kilometers) wide struck southwestern Egypt's vast sea of shifting sand dunes tens of millions of years ago.

Farouk El-Baz, director of Boston University's (BU) Center for Remote Sensing, named the double-ring impact crater Kebira, the Arabic word for "large." The name also refers to the crater's Gilf Kebir region location. The crater El-Baz and his BU colleague Eman Ghoneim found is 19 miles (31 km) in diameter. "Kebira may have escaped recognition because it is so large — equivalent to the total expanse of the Cairo urban region from its airport in the northeast to the pyramids of Giza in the southwest," says El-Baz.

Kebira dwarfs 0.7-mile-wide (1.2 km) Meteor Crater in Arizona; Kebira is more than 25 times Meteor Crater's width. The chunk of rock that carved Kebira out of desert sandstone was likely larger than the whole of Meteor Crater.

Wind and water also helped obscure the crater's features. "The courses of two ancient rivers run through it from the east and west," says Ghoneim. However, scientists suspected an impact had occurred in the region long before Kebira was discovered. Fragments of yellow-green silica glass found strewn across the desert floor, called Desert Glass, suggested an impact took place sometime in the past. High temperatures, like those produced during an asteroid impact, transform sand to silica glass. An examination of images snapped from a satellite's vantage point revealed the crater.

Kebira is the largest impact crater found to date in the Sahara Desert, but at least 20 other impact craters on Earth are even bigger. The three largest are Chicxulub Crater in Mexico's Yucatan at 112 miles (180 km) wide; Sudbury Crater in Ontario, Canada, at 155 miles (250 km) in diameter; and South Africa's enormous Vredefort Crater, which spans 186 miles (300 km) rim to rim.
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