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The Theory of Plate Tectonics

The theory of plate tectonics fundamentally transformed our understanding of Earth's geology. It posits that the planet's outer shell, or lithosphere, is divided into several large and small rigid plates that float on the semi-fluid asthenosphere beneath. These plates are in constant, slow motion, interacting with each other at their boundaries. This movement is the primary driving force behind many of Earth's most dramatic geological phenomena, including earthquakes, volcanic eruptions, and the formation of mountain ranges. The theory provides a unifying framework for explaining these seemingly disconnected events.

There are three main types of plate boundaries, each characterized by a distinct form of interaction. At divergent boundaries, plates move apart, allowing magma from the mantle to rise and create new crust, as seen at the Mid-Atlantic Ridge. At convergent boundaries, plates collide. This can result in one plate sliding beneath another in a process called subduction, which often creates deep ocean trenches and volcanic arcs. Alternatively, the collision of two continental plates can thrust up massive mountain ranges, such as the Himalayas. Finally, at transform boundaries, plates slide horizontally past each other, a motion that frequently generates powerful earthquakes, like those along California's San Andreas Fault.

The evidence supporting plate tectonics is extensive and comes from various scientific disciplines. Fossil records show identical species on continents now separated by vast oceans, suggesting they were once joined. The magnetic striping on the ocean floor provides a record of Earth's magnetic field reversals, symmetrically aligned on either side of mid-ocean ridges, confirming seafloor spreading. Furthermore, GPS technology now allows scientists to directly measure the slow, continuous movement of the plates, providing definitive proof of this dynamic geological process.