Biogeochemical cycles #1 1. ELC is an independent organization 2. Health, living conditions, technological development, the economic future, and our relationship with nature are all shaped by environmental actions. 3. The Earth is a closed system for matter, except for small amounts of cosmic debris that enter the Earth's atmosphere. 4. This means that all the elements needed for the structure and chemical processes of life come from the elements that were present in the Earth's crust when it was formed billions of years ago. 5. carbon, nitrogen, oxygen, hydrogen, sulfur, and phosphorus are critical components of all biological life. 6. 80% of the weight of human being is oxygen and carbon. 7. Carbon, however, is relatively rare in the Earth's crust, and nitrogen, though abundant in the atmosphere, is in a form that is not useable by living organisms. 8. Each cycle takes many different pathways and has various reservoirs, or storage places. 9. Elements may reside for short or long periods of time. Carbon atoms in deep ocean sediments may take hundreds to millions of years to cycle completely through the system. An average water molecule resides in the atmosphere for about ten days, although it may be transported many miles before it falls back to the Earth as rain. 10. How fast substances cycle depends on (1) its chemical reactivity and (2) whether or not it can be found in a gaseous state. 11. A gaseous phase allows molecules to be transported quickly. 12. Phosphorous has no gaseous phase and is relatively unreactive, so it moves very slowly through its cycle. Phosphorus is stored in large amounts in sediment in the oceans or in the Earth's crust and is recycled back to the surface only over very long periods of time through upwelling of ocean waters or weathering of rocks.