Dan McKenzie’s work focuses on the mechanics of the Earth. With Robert L. Parker he wrote the earliest paper on plate tectonics. Since then he has made a general study of the history of the ocean basins. In his paper with Jason Morgan on the geometry of the motion of three plates on a sphere, he found a beautiful explanation of the ‘great magnetic bight’ in the Pacific, which had been one of the principle difficulties in the acceptance of plate tectonics. Dan’s other papers have studied the cooling of a plate after it is formed on the ridge axis, and accounted for the broad variations of ocean depth and heat flow across a ridge. His interests also include the theory of convection in the mantle, and the generation of magma, its separation from its source regions and its geochemistry.