1. Systems are collections of components that interact within a boundary. Biogeochemical cycles are examples of systems involving interactions between the atmosphere, hydrosphere, lithosphere and biosphere. 2. Biogeochemical cycles describe the movement and exchange of essential chemical elements between living and nonliving parts of the Earth. 3. Biogeochemical cycles are important because they regulate the supply of critical nutrients needed to sustain life on Earth, such as carbon and nitrogen. 4. What is common amongst biogeochemical cycles is that elements exist in pools within the Earth system and undergo transformations as they move between pools through fluxes, often facilitated by biological and geological processes.