What is isostasy in geology?

Isostasy in geology refers to the balance of the lithosphere (the rigid outer layer of the Earth) floating on the semi-fluid asthenosphere (the upper part of the mantle). This concept is crucial for understanding how different geological features, such as mountains and ocean basins, achieve equilibrium based on their density and thickness. When forces such as erosion or the addition of ice weigh down the lithosphere, it will sink further into the asthenosphere until a new equilibrium is reached. Conversely, when material is removed, the lithosphere can uplift. This balance is vital for explaining phenomena related to topography and tectonics.

Other options address different geological concepts that are not related to isostasy. For instance, the pressure exerted by fluids beneath the surface pertains more to hydrogeology and not the balance of Earth's layers. Meanwhile, the mention of a type of fault that causes buckling relates to tectonic processes but does not define isostasy. Lastly, the process of heat conduction in rocks does not reflect the concept of buoyancy and equilibrium that characterizes isostasy. Thus, the correct answer encapsulates the essence of how the Earth's crust balances itself atop the underlying mantle.