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The Theory of Plate Tectonics

The idea that continents are not fixed in place but have moved over geological time is central to the modern theory of plate tectonics. However, this concept was not always accepted. In the early 20th century, German scientist Alfred Wegener proposed the theory of "continental drift," suggesting that the continents were once joined together in a single supercontinent he named Pangaea. Wegener supported his theory with evidence such as the complementary shapes of coastlines, matching fossil distributions across oceans, and similar rock formations on different continents. Despite this, his theory was widely rejected by the scientific community at the time.

Wegener's primary weakness was his inability to provide a convincing mechanism to explain how entire continents could move. The scientific establishment remained skeptical for decades. It wasn't until the 1950s and 1960s that new evidence emerged, primarily from ocean floor mapping. Scientists discovered mid-ocean ridges, where new oceanic crust is formed, and deep-sea trenches, where it is destroyed. This process, called seafloor spreading, provided the missing piece of the puzzle and formed the foundation for the theory of plate tectonics, which superseded Wegener's original model.

Today, plate tectonics is the unifying theory of geology. It explains that the Earth's outer layer, the lithosphere, is broken into several large and small tectonic plates that move over the semi-fluid asthenosphere beneath. The interactions at the boundaries of these plates are responsible for most of the Earth's major geological features and events, including earthquakes, volcanoes, and the formation of mountain ranges. The theory represents a major scientific revolution, providing a comprehensive framework for understanding the dynamic processes that shape our planet.