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Plate Tectonics and Continental Drift

The theory of plate tectonics is the fundamental framework for understanding the geology of our planet. It posits that Earth's outer shell, the lithosphere, is broken into several large and small rigid plates that move over the semi-fluid asthenosphere below. The interactions at the boundaries of these plates are responsible for most of Earth's major geological features and events, including mountains, volcanoes, and earthquakes. This concept provides a unified explanation for phenomena that were once considered unrelated.

The modern theory of plate tectonics has its roots in the earlier idea of continental drift, proposed in the early 20th century by meteorologist Alfred Wegener. Wegener hypothesized that the continents were once joined together in a single supercontinent he called Pangaea and had since drifted apart. He presented several lines of evidence, such as the complementary shapes of coastlines like South America and Africa, matching fossil distributions across oceans, and similar rock formations on different continents. However, Wegener's theory was not widely accepted because he could not provide a plausible mechanism to explain how the continents moved.

It was not until the mid-20th century that Wegener's ideas were revived. Extensive mapping of the ocean floor revealed mid-ocean ridges, where new crust is formed, and deep-sea trenches, where it is subducted back into the mantle. This process, known as seafloor spreading, provided the missing mechanism for continental movement. Driven by convection currents in the mantle, it vindicated Wegener's original observations and led to the development of the comprehensive theory of plate tectonics, which remains a cornerstone of modern geology.