I. Plate Tectonics

Plate tectonics is a theory explaining how major landforms are created. In the 1960's, the theory was solidified, which transformed into explaining many phenomena such as mountain building events, volcanoes, and earthquakes. It also describes the interaction between the different layers of the Earth. Lithosphere, which is the outermost layer- is made up of the crust and mantle- is broken into large plates. Meanwhile, the plates lying on the top of a partially molten layer is the asthenosphere. The lithosphere and asthenosphere move relative to each other due to convection. This interaction is responsible for different geological formations such as the San Andreas Fault in California and the Himalaya mountain range in Asia. 

In 1912, German scientist Alfred Wegenes changed the scientific debate that continents moved over time. He published the concept about the continental drift. In this article, he suggested that 200 million years ago, Pangaea, which is a supercontinent, broke into pieces, and its parts were moving away from each other. The fragments of these supercontinents are the continents we have today. In order to support his claim, Wegener pointed to the matching rock formation and similar fossils found in Brazil and West Africa. 

In the 1950s and 1960s, the theory of continental drift was supported by new data. Harry Hess, an American geologist proposed that molten rock is rising from the asthenosphere resulting in the ridges to form. As it came to the surface, the rock cooled, making a new crust, and spreading the seafloor away from the ridge in a conveyer-belt motion. After a million years, the crust would disappear into ocean trenches at a place called the subduction zone. But there was one question with the plate tectonics theory:

Most volcanoes are found above subduction zones, but some form far away from these plate boundaries. How could this be explained?

In 1963, a Canadian geologist, John Tuzo Wilson, answered this question by proposing the idea of volcanic island chains. It is like a Hawaiian island, as they are created by fixed “hot spots” in the mantle. At the mantle, the magma forces its way upward through the moving
plate of seafloor As it moves to another hotspot, another volcanic island can be formed. 

Access this link for an interactive activity and broaden your knowledge about Plate Tectonics: