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Crater in the sand

Researchers analyzing satellite images of the Sahara have discovered the region's largest impact crater, a 31-kilometer-wide feature located in remote southwestern Egypt.

The crater's heavily eroded rim (marked by the white dashes) rises about 230 meters above the surrounding terrain, says Eman Ghoneim, a physical geographer at Boston University. The age of the crater is unknown, but the feature must be younger than 100 million years, the age of the underlying sandstone, Ghoneim and her colleague Farouk El-Baz announced last week. The ancient impact, probably caused by an asteroid about 1 km across, might be responsible for the formation of Libyan desert glass. Those mysterious chunks of fused silica, first noted by explorers in the 1930s, are found scattered across a 50-by-130-km region near the crater.

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