![]() Many others, particularly geologists, were unimpressed, hostile, even horrified. This idea of drifting continents intrigued some scientists. Although now far-flung, the continents were once joined together as a supercontinent Wegener dubbed Pangaea, or “all-Earth.” This would explain why rocks of the same type and age, as well as identical fossils, are found on either side of the Atlantic Ocean, for example. Instead, Wegener suggested, mountains form when continents collide as they drift across the planet’s surface. At the time, the prevailing idea held that mountains formed like wrinkles on the planet as it slowly lost the heat of formation and its surface contracted. In 1912, German meteorologist Alfred Wegener proposed at a meeting of Frankfurt’s Geological Association that Earth’s landmasses might be on the move. ![]() But the conceptual journey from fixed landmasses to a churning, restless Earth was long and circuitous, punctuated by moments of pure insight and guided by decades of dogged data collection. ![]() With so many lines of evidence now known, the theory feels obvious, almost inevitable. “Pretty much everything falls into place.” “It’s amazing how it tied the pieces together: seafloor spreading, magnetic stripes on the seafloor … where earthquakes form, where mountain ranges form,” says Bradford Foley, a geodynamicist at Penn State. Plate tectonics is “the first global theory ever to be generally accepted in the entire history of earth science.” Naomi Oreskes This cycle gives rise to many of Earth’s geologic wonders, as well as its natural hazards. New seafloor is created at the center of the oceans and lost as plates sink back into the planet’s interior. Moving at rates between 2 and 10 centimeters each year, some plates collide, some diverge and some grind past one another. Plate tectonics describes how Earth’s entire, 100-kilometer-thick outermost layer, called the lithosphere, is broken into a jigsaw puzzle of plates - slabs of rock bearing both continents and seafloor - that slide atop a hot, slowly swirling inner layer. The San Andreas Fault (shown) is the boundary between the Pacific and North American plates. Plate tectonics revealed how Earth’s surface features are intrinsically linked to its hot interior. Tuzo Wilson compared the impact of this intellectual revolution in earth science to Einstein’s general theory of relativity, which had produced a similar upending of thought about the nature of the universe. When plate tectonics emerged in the 1960s it became a unifying theory, “the first global theory ever to be generally accepted in the entire history of earth science,” writes Harvard University science historian Naomi Oreskes, in the introduction to Plate Tectonics: An Insider’s History of the Modern Theory of the Earth. The planet’s familiar landscapes, we now know, are products of an eons-long cycle in which the planet constantly remakes itself. Plate tectonics reveals how Earth’s surface is constantly in motion, and how its features - volcanoes, earthquakes, ocean basins and mountains - are intrinsically linked to its hot interior. But the theory of plate tectonics has rocked this picture of the planet to its core. For centuries, the outermost layer of Earth was thought to be static, rigid, locked in place.
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