Fig. 1. A generalized biosphere model showing the basic inputs and outputs of energy and materials.
Fig. 2. A schematic depiction a global, interconnected network of the biologically mediated cycles for hydrogen, carbon, nitrogen, oxygen, sulfur, and iron.The central importance of CO2 jumps out of Fig 2. Something to think about in the context of the present rapid change in its atmospheric concentration. J. E. N. Veron includes a graph (Fig 16.1) showing the concentration over for last 25 million years. The line is a little wiggly by more or less horizontal across the page (indicating values between roughly 200 and 300ppm) until the last millimetre when it shoots up (towards 1000ppm by 2100). What's really striking, though, is Veron's observation, 'if this diagram were redrawn with a horizontal axis 250 metres long, the spike [at the end] would still be a vertical line'.