The Earth's surface, in this model, is the plane and geology is involved with everything in the infinite half-space beneath that plane. Planning pipelines, tracking pollution in groundwater, laying out a mining program, scoping foundations, fixing landslides, mapping underground features, assessing the mineral potential of a piece of land are all tasks that geologists do. They can pursue any number of geologies: forensic geology, engineering geology, military geology, mining geology, environmental geology, oil & gas geology.
While it's fun and interesting and intellectually important to know about the Earth's core, things get more practically important the closer you get to the surface. Geology can be a remote, visionary field, and sure we like the mystique of being at home amid the sweep of continents in gigayears of time. But in truth, geologists are down to Earth, not buried in it. Geology is not just a good life; it's a good living.