Understanding the four major biogeochemical cycles, carbon, water, nitrogen, and phosphorus, is critical to understanding the impact that humans have on the ecology of the planet. These cycles exist independent of human activity, but are affected by humans. As such, understanding how they work and their dependencies deepens the understanding of ecological and environmental policies that may be under consideration. This research provides an examination of each of these cycles.
The global carbon cycle is driven primarily by photosynthesis and respiration; plants convert carbon dioxide from the atmosphere into sugar via photosynthesis. Animals may eat the plant and release carbon dioxide back into the atmosphere via respiration. Carbon dioxide also results when the plant dies via the decay process; the same is true when animals die and the decay process releases carbon dioxide. Fires also contribute carbon to the atmosphere, as does burning fossil fuel. There are also geological components to the carbon cycle as carbon can be produced by volcanoes (Remer, 2009).
Most of the earth's water is found in the oceans, polar ice, and groundwater; this restricts the access for most plants and animals, with humans being the major exception because humans can access water from all three sources. Water flux occurs through evapotranspiration, precipitation, and runoff. The sun heats water in the oceans, which evaporates into the atmosphere. Evapotranpiration includes evaporation from oceans as well as water vapor that evaporates from ice and snow, plus water that evaporates from soil. Evapotranpiration also includes transpiration from plants. Rising air currents lift the evapotranspired water vapor higher, where cooler temperatures result in condensation into clouds. The clouds produce precipitation, which returns water to the earth as rain
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