Seafloor spreading hypothesis

Harry Hess's 1962 proposal that new oceanic crust forms at mid-ocean ridges and carries seafloor laterally toward trenches, recycling itself.

Harry Hammond Hess: Princeton geologist who proposed seafloor spreading in 1962, calling himself 'an accordion player' for the speculative idea. He framed seafloor spreading as 'geopoetry', an explicit guess later vindicated by magnetic evidence.
Mantle convection: Slow solid-state circulation of Earth's mantle driven by heat, proposed as the engine moving plates. Hess explicitly tied spreading to convection cells rising under ridges and descending at trenches.
Vine–Matthews–Morley hypothesis: The 1963 explanation that symmetric magnetic stripes on the seafloor record reversals during spreading. The decisive test: striped magnetic anomalies proved spreading operates exactly as Hess imagined.
Expanding Earth hypothesis: The idea that Earth grows in volume, spreading the continents apart without any subduction. Its main rival in the early 1960s; abandoned once subduction balanced seafloor creation.
Plate tectonics: The unifying theory that Earth's lithosphere consists of moving plates interacting at their boundaries. Spreading was the missing mechanism that allowed the full theory to be assembled by 1967.
Marie Tharp: Cartographer whose 1950s physiographic maps of the Atlantic revealed a continuous mid-ocean ridge rift valley. Her maps made the ridge system visible, giving spreading a physical stage to occur on.
Mid-ocean ridge: The 65,000-kilometer undersea volcanic mountain chain where new oceanic crust is generated. The factory floor of the hypothesis: magma rises here to create fresh oceanic lithosphere.
Geomagnetic reversal: Episodes when Earth's magnetic field flips polarity, recorded as alternating magnetization in cooling lava. Reversals provide the clock that stamps spreading crust with dateable magnetic stripes.
Permanentist paradigm: The pre-1960s geological consensus that continents and ocean basins are fixed and unchanging. Spreading demolished the fixist orthodoxy that had rejected continental drift for decades.
Wilson cycle: J. Tuzo Wilson's model of oceans opening and closing over hundreds of millions of years. Generalized spreading and subduction into a repeating lifecycle of ocean basins.

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