Wilson Cycle

Lab 17 Part A: What is a Wilson Cycle? Early study of Plate Tectonics in the 20th Century arrived at the conclusion that if Tectonic plates being driven around on the outermost hard layer of the Earth (e.g., the lithosphere) never changed direction that the Earth should always be composed of a single, large, landmass accounting for nearly all of the continental crust. In other words, if the Theory of Plate Tectonics was to be valid, there had to be a process for plates to “go in reverse” or have forces change direction, otherwise the continents as we see them today should all be stuck together. Subsequent research has indicted that, indeed, the Earth has undergone several cycles (called “Wilson Cycles”) whereby all of the major landmasses on Earth were combined in one location, then split apart, then combined again, etc. During this process of combining and separating, the large masses of continental crust are surrounded by thinner, more-dense oceanic crust. That oceanic crust is created and added onto the edges of tectonic plates when they move apart, and that oceanic crust is destroyed (subducted) from the edges of tectonic plates when they move together. In addition, this process appears to have been repeated several times during Earth’s long history. Watch Video 01, and visualize how the last stage in the video could easily repeat to the first stage shown in the Video 01: à https://youtu.be/I_q3sAcuzIY [1:36 min YouTube video] This cartoon indicates the main phases of the Wilson Cycle. Question A.1: At first glance, when the tectonic plate containing the continental land mass splits apart, it looks like the two are moving “away” from each other. However, if one remembers that the Earth is round, you could also say the two tectonic plates are moving “towards” each other. Explain. Question A.2: At the 0:28 minute mark in Video 01 (when the continental crust of the two plates are as far apart as they will get), where are volcanoes generating new crust? Explain. Question A.3: Beginning at the 0:29 minute mark in Video 01, something changes. Briefly describe the process that occurs at the edge of the western tectonic plate, and then again discuss where there are volcanoes generating new crust. Explain.