Why Oceans Don't Drain
Oceans do not drain into the ground because they are held in tectonic depressions lined with impermeable rock, balanced by hydrostatic pressure, and regulated by a steady-state water cycle. Gravity pulls uniformly toward the center of mass, but the solid Earth provides a physical barrier that prevents downward flow. The system is stable over geological time scales.
System Stability
While small-scale processes like submarine groundwater discharge occur, they represent a net flow of freshwater *into* the ocean, not a drainage of ocean water *out*. The overall volume and containment of the oceans remain secure due to the combined effects of geology and physics.