powered by solar energy, which is fine-tuned and directed by energy expended by organisms. In a sense, the solar-energy-powered hydrologic cycle(Figure 3. 1)acts as an endless conveyer belt to move materials essential for life through ecosystem herge through Oxygen Synthesis of Figure 1. 2. Energy conversion and transfer by photosynthesis Figure 1.3 shows a general cycle with all five spheres or reservoirs in which matter may be contained. Human activities now have such a strong influence on materials cycles that it is useful to refer to the"anthrosphere'"along with the other environmental"spheres" as a reservoir of materials. Using Figure 1.3 as a model,it is possible to arrive at any of the known elemental cycles. Some of the numerous possibilities for materials exchange are summarized in Table 1.1 C 2000 CRC Press LlCpowered by solar energy, which is fine-tuned and directed by energy expended by organisms. In a sense, the solar-energy-powered hydrologic cycle (Figure 3.1) acts as an endless conveyer belt to move materials essential for life through ecosystems. Figure 1.2. Energy conversion and transfer by photosynthesis. Figure 1.3 shows a general cycle with all five spheres or reservoirs in which matter may be contained. Human activities now have such a strong influence on materials cycles that it is useful to refer to the “anthrosphere” along with the other environmental “spheres” as a reservoir of materials. Using Figure 1.3 as a model, it is possible to arrive at any of the known elemental cycles. Some of the numerous possibilities for materials exchange are summarized in Table 1.1. © 2000 CRC Press LLC