Oceanic thermal subsidence ($d(t)-d_r\propto \sqrt{t}$)

Cooling oceanic lithosphere contracts and increases its column mass, causing isostatic deepening. Integrating a half-space cooling profile gives an excess mass proportional to $\sqrt{t}$. Converting this to seafloor depth includes the density contrast between mantle and seawater. Finite-plate cooling and basal heat supply limit indefinite square-root subsidence at old ages.