concept

Hydrostatic pressure

The pressure exerted by the weight of the water column above, rising by about 0.1 MPa — near enough one atmosphere — every 10 m of descent. At the bottom of the deepest trench that is roughly 1,100 atmospheres, which sounds like a death sentence. But water is very nearly incompressible (about 4.5×10⁻¹⁰ per pascal), and tissue is mostly water, so even 110 MPa squeezes it by only a few per cent. Pressure deforms things only when it is unbalanced — more on one side of a wall than the other — so a gas-filled cavity is in danger while a gas-free body is squeezed identically from every direction with nothing to fail. What pressure actually breaks is molecular: enzymes slow, membranes stiffen.