Biogeochemical+Cycles

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Earth is a complex, evolving body characterized by ceaseless change. To understand Earth on a global scale means using a scientific approach to consider how Earth's component parts and their interactions have evolved, how they function, and how they may be expected to further evolve over time. This visualization adapted from NASA helps explain why understanding Earth as an integrated system of components and processes is essential to science education.

Click on the link below to watch the short video. [|Earth as a System]

A biogeochemical cycle is the cycle that a single chemical takes through nature. For instance, nitrogen in the atmosphere is broken down by certain bacteria in the soil. Plants growing in that soil use the nitrogen; then, they get eaten by an animal. That animal dies and decomposes. More bacteria eat the decaying tissues and eventually convert the nitrogen back into a gas. The nitrogen has traveled through a cycle of air, bacteria, soil, plant, animal, bacteria, air. Nothing Lost No chemical is ever considered to be lost in a biogeochemical cycle. Sometimes the chemical may be held somewhere for a very long time, such as the carbon that is in coal deposits deep in the earth, but it is still there. That kind of holding place for a chemical is called a reservoir, and they are generally non-organic. Exchange pools are the steps of the cycle that don't last very long; they are usually organic. Given enough time, all chemicals will cycle through both organic and inorganic factors. Chemicals of Life The kinds of chemicals that are studied in biogeochemical cycles are ones that are used by living organisms. They include oxygen, nitrogen, carbon, phosphorous, sulfur and water. Following the progress of a single chemical through air, earth and organism illustrates the connectivity of nature and the dependence of living beings on their environment and vice versa. It also illustrates the point the recycling is a fundamental principle in nature.



The Water Cycle One of the easiest biogeochemical cycles to explain is the water cycle, or hydrological cycle. First, water vapor in the atmosphere condenses into liquid due to cold temperatures. It falls to the earth as rain and either soaks into the ground or runs off into rivers. Great heat causes the liquid to evaporate, or turn back into a gas. You can also add to that the water absorbed by plants and drunk by animals, which returns eventually by way of drying up, sweat, urine and other means.



 The Carbon Cycle Carbon dioxide is the gaseous form of carbon which fills our atmosphere. It is absorbed by plants through photosynthesis and used to make carbon-based plant food. When those plants get eaten, the carbon passes onto that animal -- or else they decay, and the carbon goes into the ground. From one animal, the carbon may pass onto another animal by eating and eventually will either be breathed out in the form of carbon dioxide, or it go into the earth when the animal dies. The stored carbon in organic matter can turn in time into coal, to be released only when it gets dug up and burned.

 The Nitrogen Cycle All plants and animals need nitrogen to make amino acids, proteins and DNA, but the nitrogen in the atmosphere is not in a form that they can use. The molecules of nitrogen in the atmosphere can become usable for living things when they are broken apart during lightning strikes or fires, by certain types of bacteria, or by bacteria associated with bean plants.

Most plants get the nitrogen they need to grow from the soils or water in which they live. Animals get the nitrogen they need by eating plants or other animals that contain nitrogen. When organisms die, their bodies decompose bringing the nitrogen into soil on land or into ocean water. Bacteria alter the nitrogen into a form that plants are able to use. Other types of bacteria are able to change nitrogen dissolved in waterways into a form that allows it to return to the atmosphere.

Certain actions of humans are causing [|changes to the nitrogen cycle] and the amount of nitrogen that is stored in the land, water, air, and organisms. The use of nitrogen-rich fertilizers can add too much nitrogen in nearby waterways as the fertilizer washes into streams and ponds. The waste associated with livestock farming also adds large amounts of nitrogen into soil and water. The increased nitrate levels cause plants to grow rapidly until they use up the supply and die. The number of plant-eating animals will increase when the plant supply increases and then the animals are left without any food when the plants die.