Earth & Cosmos / Earth, Climate & Environment

Mapping the ocean floor

Marie Tharp and Bruce Heezen's sonar-based maps (1957) revealed a rift valley along the Mid-Atlantic Ridge.

Using echo-sounder profiles collected by Heezen's ships, Marie Tharp drew the first detailed physiographic map of the North Atlantic floor, published in 1957 (a fuller version followed in 1959), and noticed a deep rift valley running down the Mid-Atlantic Ridge. Earthquake epicentres plotted along it supported the idea that the sea floor is being pulled apart. The maps became key evidence for sea-floor spreading and plate tectonics.