ABSTRACT
The Earth’s surface – the toposphere – sits at the interfaces of the solid lithosphere, the gaseous atmosphere, and the watery hydrosphere. It is also the dwelling-place of many living things. Gases, liquids, and solids are exchanged between these spheres in three grand cycles, two of which – the water or hydrological cycle and the rock cycle – are crucial to understanding landform evolution. The third grand cycle – the biogeochemical cycle – is the circulation of chemical elements (carbon, oxygen, sodium, calcium, and so on) through the upper mantle, crust, and ecosphere, but is less significant to landform development, although some biogeochemical cycles regulate the composition of the atmosphere, which in turn can affect weathering.
