Corals keep eruption record.

When the Indonesian volcano Krakatau exploded in 1883, it blew so much dust and gas into the atmosphere that it turned sunsets red around the globe for months. Keepsakes of that debris have now turned up lodged inside the skeletal structure of coral off the Florida Keys, reports Elizabeth A. Merman of the University of South Florida in St. Petersburg.

Corals produce annual bands as they grow, making it easy for researchers to date specific layers. Looking at a band from the mid-1880s, Merman and her coworkers found a distinctive mixture of elements matching that of rock from the Krakatau eruption. The same combination didn't appear in any other band before or after the eruption, she reported in San Francisco at a meeting of the American Geophysical Union last month.

Researchers could use this technique to trace dust from many sources, such as storms of sand blowing off the Sahara toward the United States. "There is information being held within these [coral] skeletons," says Merman.