David Sandwell uses satellites to make accurate measurements of the shape of the ocean surface.  He explains how this enabled him to create a global map of the topography on the sea-floor.  This revealed the global extent of classic plate-tectonic features, such as spreading ridges and transform faults, but also intriguing new features we still do not understand.

David Sandwell is a Professor at Scripps Institution of Oceanography at the University of California San Diego.