The earth s crust is composed of a mixture of lighter elements that are more available to organisms. During the formation of the earth, many of the heavier elements sank to the earth s core. Because life as we know it only exists on the surface of the planet, these are but a small subsample of elements on earth that life can utilize. In Chapter 4 and in the next study guide, we will see that the rates of weathering and other soil processes control the availability of these nutrients. Organisms in ecosystems require nutrients, and plants are the main group for extracting them from the environment.
Essential elements come from atmospheric inputs and weathering from the soil.
Their natural availability sets the stage for a number of ecosystem processes such as species composition and site productivity. An extremely important source of nutrients is rock weathering. Comparison of energy and material cycling paradigms Like energy, elements flow through the ecosystem as they are taken up by autotrophs, which are then eaten by herbivores, which are eaten by carnivores, and so on. Matter cycling differs from energy, however, in that energy is lost at each step in the food chain. Elements like N, C, P, S, Mg, K, and Ca can be cycled over and over thanks to decomposers that break down dead organisms and resupply nutrients to autotrophs.