Knowra Plate tectonics Plate tectonics The theory that Earth's rigid outer shell is broken into moving plates that interact at their boundaries, driving earthquakes, volcanism and mountain building.
Seafloor spreading : The creation of oceanic crust at mid-ocean ridges as magma rises and plates diverge. The process that both moves plates apart and records their motion in the ocean floor.
Continental drift : Alfred Wegener's 1912 hypothesis that continents move across Earth's surface, rejected for lacking a mechanism. The precursor theory whose evidence survived and whose missing mechanism plate tectonics supplied.
Mid-Atlantic Ridge : The divergent boundary running down the Atlantic, separating the Eurasian and North American plates. The classic spreading center, walking distance across in Iceland.
Pangaea : The supercontinent that assembled about 335 million years ago and broke apart beginning in the Jurassic. Plate reconstructions turned Pangaea from hypothesis into a mapped episode of Earth history.
Mantle plume : A hypothesized column of hot rock rising from deep in the mantle, feeding intraplate volcanism like Hawaii. Whether plumes exist as drawn, and how they relate to plates, remains contested.
Subduction : The sinking of a dense oceanic plate into the mantle beneath an overriding plate at a convergent boundary. Slab pull from sinking plates is now considered the dominant force driving plate motion.
Alfred Wegener : German meteorologist who gathered evidence for continental drift and published it in 1915. The theory's founding figure, ridiculed in his lifetime and vindicated decades later.
San Andreas Fault : The transform boundary where the Pacific plate slides northwest past the North American plate. The textbook transform boundary, source of California's earthquake hazard.
Wilson cycle : The repeated opening and closing of ocean basins over hundreds of millions of years. The grand pattern of plate motion: oceans are born, widen, shrink and close.
Archean tectonics : The question of whether plate tectonics operated on the early Earth more than 2.5 billion years ago. When plates began moving is one of geology's live debates.
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