Earth’s oceanic crust averages only about seven kilometers thick
Under the oceans, Earth’s crust is a thin basaltic shell averaging roughly seven kilometers thick — far slimmer than continental crust, which often runs 30–50 kilometers deep.
That thinness lets seafloor spread and subduct relatively easily, recycling into the mantle at trenches. Continents float thicker and buoyant, resisting subduction and preserving ancient rock.
Thickness decides destiny. Earth’s dual crust — thin ocean, thick land — is why plate tectonics can run, something no other solar-system planet clearly repeats.
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