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Seismic profile. Geologist on a research ship printing out a seismic profile of the oceanic crust. Seismic profiling uses loud sound sources (such as airguns) to create seismic waves in rock. The reflected sound is detected with hydrophones (underwater microphones) and analysed to find out about the structure of the rock below. The printout shows the layers in a slice through the ocean floor. The vessel is the British Antarctic Survey's Royal Research Ship James Clark Ross. Photographed in the East Scotia Sea in 1996. (KEYSTONE/SCIENCE PHOTO LIBRARY/BRITISH ANTARCTIC SURVEY)