What two theories does the theory of plate tectonics unite?
The Theory of Plate Tectonics
The theory of plate tectonics shows that Earth's lithosphere is composed of tectonic plates that move around and create the landscape of Earth. These plates move at a rate of a few centimeters per year. Plates can move apart at mid-ocean ridges where new seafloor forms, towards each other causing volcanoes to form, or past each other to create earthquakes.
Answer and Explanation:
Earth's outer shell, called the crust, is part of the lithosphere and lies on top of the semi-molten asthenosphere. The lithosphere is broken up into plates that move at about 2 centimeters per year on top of the asthenosphere. Before the theory of plate tectonics, scientists had no way of explaining geologic features such as mountains, oceans, continents, earthquakes, and volcanoes. One theory scientists had was seafloor spreading, where new crust forms on the ocean floor because of magma coming up through mid-ocean ridges and the ocean floor spreading as a result of it. The other theory was continental drift, which explained how continents fit together like a jigsaw puzzle, and since the formation of the continent Pangea, have drifted apart to where they are today. Plate tectonics unified these two previous theories by saying that the reason for the geologic features observed and the observation of continents appearing to drift is driven by the relative motion of these plates.
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from General Studies Earth & Space Science: Help & ReviewChapter 7 / Lesson 5