'Discuss the geochemical cycle of the element sulfur' - Essay Example

Sulfur occurs in nature and it is also present in coal, crude oil, natural gas, oil shale and many other minerals. The most abundant of all sulfur is a compound of sulfur and iron called pyrite. Sulfur cycle is a major biogeochemical cycle of significance to climate and life on the planet earth. Living things require certain safe, low levels of this nutrient. It is an essential component of proteins and amino acids. All plants and animals require small amounts of sulfur to live. Plants obtain sulfur form soil.

Many foods from plants including cabbage, onion, and soybean flour are rich in sulfur. Methionine a substance required in the human diet also contains sulfur. It is also present in the foods such as eggs, dairy products and meats. In nature sulfur exists in various forms such as elemental sulfur, sulfides, sulfites, sulfates, oxides of sulfur, etc. However the majority mainly occurs in the form of elemental sulfur, sulfides and sulfates. Early earth ecosystems with well developed sulfur cycles thriving in environments receiving reduced sulfur gases (and H2) from the mantle.

Such environments might include recirculating hydrothermal systems as found in areas of ocean crust formation and places of active terrestrial volcanism. These environments were likely thermophilic to hyperthermophilic with primary production occurring by anaerobic photosynthesis when light was available. In the absence of light, organic matter production occurred by chemolithoautotrophic metabolisms utilizing H2 as the electron donor and oxidized species such as elemental sulfur (forming H2S) or carbon dioxide (forming methane) as the electron acceptors.

Organic compounds were oxidized by the reduction of elemental sulfur and sulfate (chemoheterotrophic metabolisms), as well as by the fermentation of acetate, producing methane. Elemental sulfur was produced by the reaction between H2S and SO2, while anaerobic photosynthesis was an important source of sulfate. The evolution of