Further Reading

Chaisson, Eric, and Steve McMillan. Astronomy Today.

6th ed. New York: Pearson/Addison-Wesley, 2007. Comins, Neil F. Discovering the Universe. 8th ed. New

York: W. H. Freeman, 2008. Snow, Theodore P. Essentials of the Dynamic Universe: An

Introduction to Astronomy. 4th ed. St. Paul, Minn.:

West, 1991.

geochemical cycles Geochemical cycles refers to the transportation, cycling, and transformation of the different chemical elements through various reservoirs or spheres in the Earth system, including the atmosphere, lithosphere, hydrosphere, and biosphere. The cycles occur through a great variety of processes, timescales, and different reservoirs or systems within the whole Earth system. Geochemical cycles are characterized by a closed flow in the Earth system; if the system is fully defined, the particular element remains in the same abundance in the cycle but moves from location to location by a series of processes. In other words, there is a material balance in geochemical cycles. The most basic picture of a geochemical cycle is analogous to the rock cycle, where molten magma rises from the deep interior of the Earth, crystallizes to form an igneous rock, then erodes to form a sedimentary rock, which gets buried and becomes a metamorphic rock, which eventually is heated to become a magma that rises back to the surface.

All geochemical cycles have a characteristic time necessary for completion. The longest is the geo-chemical cycle that brings material from deep within the Earth to form midocean ridges that then form oceanic crust that gets subducted, returned to the deep mantle to eventually rise back to the surface. This cycle takes from several hundred million years to about 4.5 billion years by some estimates.

The material balance of chemical elements in a geochemical cycle can be complex and includes

Continue reading here: Geochemical cycles

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