Life and Biogeochemical Cycles

Biogeochemical cycle. As discussed early in the chapter, this term describes the global or regional cycles of the "life elements" C, N, S, and P with reservoirs including the whole or part of the atmosphere, the ocean, the sediments, and the living organisms. The term can be applied to the corresponding cycles of other elements or compounds. 

Repeated splitting of lineages of organisms into separate species has resulted in the great richness and diversity of life that lived in the past and is found on Earth today. Earth would be very different if speciation had been a rare event during the life s history. Biogeochemical cycles are influenced by millions of species, each adapted to live under a particular range of conditions and to use environmental resources in a particular way. 

The evolution of life on Earfh has depended on a sustained supply of nutrients provided by the physical environment. Life, in turn, has profoundly influenced the availability and cycling of these nutrients hence the inclusion of bio in biogeochemical cycles. The involvement of the biosphere with biogeochemical cycles has been determined by the evolution of life s biochemical properties in the context of the physical and chemical properties of planet Earth. 

Although there are three Rji isotopes in the U- and Th-decay series, only is sufficiently long lived tm= 3.8 days) to be a useful estuarine tracer. Radioactive decay of Ra continuously produces Rn, which because of its short half-life is generally in secular equilibrium in seawater. Being chemically non-reactive except for very weak Van der Waals bonding makes this isotope a unique marine tracer in that it is not directly involved in biogeochemical cycles. 

Biogeochemical cycling of elements and pollutants exposure pathways in the tropical ecosystems, which occur between 30°N and 30°S, are both intensive and at high probability of risk for human and ecosystem health. The tropical belt receives about 60% of solar radiation inputting on the Earth s surface. The total area of tropical ecosystems is about 40 x 106 km2, with exception of the High Mountain and Extra-Dry Sandy Deserts with strongly depressed life processes. 

The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs the atmosphere, the biosphere, and the lithosphere. The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth s atmosphere and life. 

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