1.) The field of study involving the complex interactions of the biotic and abiotic world and how elements cycle through the Earth.
2.) A series of impossibly complex chemical equations, most likely about soils, that you could never hope to understand that also gives rise to the suspicion that no one really gets it.
3.) What you tell your friends you study when you want to sound smarter than them.
Plants used to grow out of the dirt until I took biogeochemistry, now I don't even know what dirt is.