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The Theory of Plate Tectonics

Plate tectonics is the modern, unifying theory of geology that explains the large-scale movements of Earth's lithosphere. The lithosphere, which is the planet's rigid outer layer, is broken into several large and numerous smaller pieces called tectonic plates. These plates are not static; they float on the semi-fluid asthenosphere beneath them and are in constant, slow motion. The theory explains a vast range of geological phenomena, including the formation of mountains, the occurrence of earthquakes and volcanoes, and the shapes and locations of the continents. There are three main types of plate boundaries: divergent, convergent, and transform.

At divergent boundaries, tectonic plates are moving away from each other. This process, known as seafloor spreading, allows magma from the mantle to rise and cool, creating new oceanic crust. The Mid-Atlantic Ridge is a classic example of a divergent boundary. In contrast, at convergent boundaries, plates move toward one another. When an oceanic plate collides with a continental plate, the denser oceanic plate is forced to subduct, or sink, beneath the continental plate. This process can form deep ocean trenches and volcanic mountain ranges, such as the Andes in South America.

The third type of boundary is a transform boundary, where plates slide horizontally past one another. The motion is not smooth, and the plates can lock, building up stress that is eventually released in the form of an earthquake. The San Andreas Fault in California is a well-known transform boundary. The theory of plate tectonics, developed in the mid-20th century, provided a comprehensive framework that connected many previously disparate geological observations, revolutionizing our understanding of the dynamic planet on which we live.