I graduated from UCSC with a Masters degree in Earth Science, so I'm obviously a little bias, but none the less; I think there is nothing more awesome than the forces of nature which shape our planet, and ultimately prescribe the boundaries we humans (and all animals) must live within.
Water
Water is one of the most remarkable of the Earth shaping forces, and the one mineral that ALL life as we know it requires in order to survive.
Geology
and you thought it was just a rock!?!