Dynamics of Biological Systems, Chapter 5: Basics of Plant Growth

First paragraph. The sun is the ultimate energy source for the biosphere. Using the terminology of the second law of thermodynamics, this statement is equivalent to saying solar energy decreases the entropy of the biosphere. Processes in the biosphere continually lose heat to their surroundings, and without the continuous influx of solar energy, energy-exchange processes (and thus life) on earth would cease. Solar energy can be a direct input to natural and agricultural ecosystems (as solar radiation) or an indirect input (as wind, heat, rain, water flow, etc.). In agricultural ecosystems, fossil fuels (a very concentrated form of solar energy) also serve as significant energy inputs. Ecosystem outputs include heat and various processed forms of energy (such as food and organic waste products).