Helpful H-Bomb

IN THEIR QUEST FOR KNOWLEDGE, SCIENTISTS WILL take advantage of anything that's helpful, even a nuclear blast. Studies of the shock waves given off by a Chinese .66-megaton nuclear test have revealed a "continent" 2,000 miles underground, at the boundary between the molten iron of the planet's core and the molten rock just above it. The word continent is used loosely; what two scientists at the U.S. Geological Survey found was a region 200 miles across and 80 miles deep that is denser than surrounding regions. The implication: the core-mantle boundary may be as complex as the earth's surface.

When the Bomb sent shock waves through the earth, ripples were detected at North American seismic centers. Because a wave's speed depends on the composition of what it's moving through, the timing of detections helped scientists compare densities of subterranean regions. This type of research may uncover other structures inside the earth, but -- fortunately -- H-bombs don't go off every day.