From Science News: A wealth of data from petrified lightning.

The lumps of glass created when lightning strikes sandy ground can preserve information about ancient climate, new research indicates.

Worldwide, lightning flashes occur about 65 times per second. Each bolt releases as much energy as is stored in a quarter-ton of TNT. The flash heats the air to about 30,000°C, about five times the temperature of the surface of the sun. If that electrical discharge strikes sandy ground, it can melt and then fuse sand and other materials into masses of glass called fulgurites, says Rafael Navarro-González, a geochemist at the National Autonomous University of Mexico in Mexico City. Those masses take their name from fulgur, the Latin word for lightning.

Although thunderstorms are common in many parts of the world, they’re rare in the desert of southwestern Egypt. "Satellite data gathered between 1998 and 2005 detected little, if any, lightning in that area," says Navarro-González. However, the lumps and tubes of glass that litter the region’s shifting dunes are proof that lightning, the only source of fulgurites, frequently touched down there in the past.

(I removed the link to Science News, as the article is no longer on their website.)