According to Nicholas van der Elst, a seismologist at Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, plate tectonics is the unifying theory of geology (Oskin, 2014). These plates are divided up into three main categories: major plates, minor plates, and micro plates. The seven largest plates are the African, North American, South American, Eurasian, Indian-Australian, Antarctic, and Pacific plates (Sipiera, 1998). These plates are constantly moving and shifting at small rates. These movements create three types of plate tectonic boundaries: divergent, convergent, and transform boundaries. Plate tectonic movement can be difficult to understand as many active areas converge with multiple boundaries. This theory of movement was first introduced in 1596 by Abraham Ortelius. His theory was later referred to as, continental drift. This theory was more fully developed in 1912 by Alfred Wegener. By 1958, Wegener's theory was more fully developed and accepted as plate tectonics.