All the ways the earth can murder you (natural disasters)
Psudo-geology of Jupiter as compared to Earth
Sulfuric-acid caves in South America
Hypothetical/Theoretical future of Earth over a long period of time
Different ways that geology can be manipulated and/or harvested to solve major world problems
Possible/alternate outcomes of the Earth
Geological obstacles that have/have not been overcome
Unknown mysteries of geology, and speculation of theories
Similarities between Earth and other (previously) geologically active planets