A Spark in the Sand

It's hard to believe that something as ephemeral as lightning could be frozen in time for thousands of years. But that's just what happens with fulgurites--glassy, hollow tubes that form when lightning melts sand. For the first time, researchers have successfully dated these unusual geological formations, and the findings are providing a unique insight into the long-ago climate and ecology of the Sahara desert.

Fulgurites record the past by providing direct evidence of thunderstorms and rain. But when Rafael Navarro-González, a chemist at the National Autonomous University of Mexico in Mexico City, came across an unusual specimen from the Sahara desert in southwestern Egypt, he realized that some fulgurites may have a much more interesting story to tell. Unlike most fulgurites, this one was rounder and solid, but what really caught his eye were tiny, embedded glass bubbles. He wondered if they might contain gas.