After Alfred Wegener died, his idea of continental drift refused to die with him. Scientists continued to examine the idea of continental drift and eventually the concept of seafloor spreading was developed. In 1960, a professor from Princeton University, by the name of Harry Hess developed the new theory of seafloor spreading. This is the idea that a new ocean crust forms at spreading centers, most commonly on the ocean floor, and then pushes the continents aside. In 1965, the two theories of continental drift and seafloor spreading were combined to produce the concept of plate tectonics. The theory of plate tectonics says that Earth's outer layer is comprised of several lithospheric plates floating around on the athenosphere. When these plates are heated, the athenosphere expands and begins to rise dragging the lithospheric plates with it. .
There are three types of plate boundaries: divergent plate boundaries, convergent plate boundaries and transforming plate boundaries. Divergent plate boundaries are regions were plates are moving apart. As a result, new ocean or rift valley with eventually form and a spreading center forms at the junction. Convergent plate boundaries are regions where the plates are pushing together and because of this a mountain range, island arc or trench will eventually form. Transforming plate boundaries where the crustal plates shear laterally past one another. Crust is not produced or destroyed. .
The major features of the ocean floor are all related to plate movements. Mid-ocean ridges are spreading centers. When Harry Hess and Robert Dietz were investigating the features of the ocean floor and the continents they suggested the idea that new seafloor develops at mid-ocean ridges and then spreads outward. This idea is seen in divergent plate boundaries. Here a ridge forms at the spreading center. Plate tectonics explains the formation of guyots. Guyots are flat-topped, submerged, inactive volcanoes.