Plate tectonics is the model that treats Earth's outer shell as a set of rigid plates drifting over a ductile mantle — colliding, pulling apart, and grinding past one another. It displaced the older assumption that continents had stood fixed since the planet first cooled.
The case for drifting continents was first argued in detail by Alfred Wegener in 1915, and given a workable mechanism half a century later by seafloor-spreading work from Harry Hess and the magnetic surveys of Fred Vine and Drummond Matthews. Wegener rested his argument on matching coastlines and shared fossil beds — evidence his contemporaries dismissed for want of a driving force.
The consequences reached well past geology. Tectonics explained why earthquake belts and volcanic arcs trace the same narrow seams, why the deepest ocean trenches sit beside the youngest island chains, and why rock at a mid-ocean ridge is measured in millions of years while continental cores run to billions.
Resistance held for roughly four decades, mostly among geologists who wanted a physical driver before they would accept the motion. Paleomagnetic stripes read from the Atlantic floor supplied it: symmetric bands of reversed polarity on either side of the ridge, a tape recording of the seafloor widening. By the late 1960s the model was standard, and it remains the frame for how we read mountain belts, rift valleys, and seismic risk today.
References
- Wegener, A. (1915). Die Entstehung der Kontinente und Ozeane.
- Hess, H. H. (1962). History of Ocean Basins.
- Vine, F. J. & Matthews, D. H. (1963). Magnetic Anomalies over Oceanic Ridges.
- Wilson, J. T. (1965). A New Class of Faults and Their Bearing on Continental Drift.
- Oreskes, N. (1999). The Rejection of Continental Drift: Theory and Method in American Earth Science.