Using detailed seismic data, scientists have obtained the clearest picture yet of the earth's inner workings. The images provide long-awaited direct evidence for mantle plumes--large columns of heat emanating from the planet's interior--which were first predicted in the 1970s.

Raffaella Montelli of Princeton University and her colleagues analyzed findings from more than 3,000 seismographic stations around the world that had monitored movement of some 86,000 earthquakes since 1964. The speed at which the resulting seismic waves move through the earth depends in part on the temperature of the rock. Based on the observed differences in speed, the team assembled a 3-D temperature map of our planet that is described in a paper published online today by the journal Science. When the researchers compared the heat columns in their map to suspected sites of mantle plumes around the globe, they identified 32 plume locations. Some are well-known so-called hot spots, such as those underneath Tahiti and the Hawaiian islands, whereas others are new to science. "This is the first visual evidence that mantle plumes exist," Montelli says. The mapping technique is not foolproof, however. Some expected plumes--including one thought to lie underneath Yellowstone National Park--did not appear.

Montelli next plans to repeat the analysis using different types of seismic waves in order to refine the images. "Some plumes may be gaining strength and other may be fading," says Jason Morgan of Princeton, who first proposed the existence of mantle plumes but did not work on this project. "I don't know what will come of that, but it will be something interesting I am sure."