Hydrogen compounds, marine organic

Although how they were produced is not completely understood, petroleum and natural gas were most likely formed from the remains of marine organisms that lived about 500 million years ago. Petroleum is a thick, dark liquid composed mostly of compounds called hydrocarbons that contain carbon and hydrogen. Table 9.5 lists the formulas and names of several common hydrocarbons. Natural gas, usually associated with petroleum deposits, consists mostly of methane but also contains significant amounts of ethane, propane, and butane. 

Although we do not really understand completely how petroleum deposits were formed, they most likely came from the remains of marine organisms living over 500 million years ago. Petroleum is composed of hydrocarbon compounds (which contain only carbon and hydrogen). Carbon is a unique element in that it can produce chains of atoms in a molecule of different lengths. Table 4.4 gives the names and formulas of some simple hydrocarbons. Natural gas is associated with petroleum deposits and consists mainly of methane with some ethane, propane, and butane mixed in. 

Dissimilatory sulfate reducers such as Desul-fovibrio derive their energy from the anaerobic oxidation of organic compounds such as lactic acid and acetic acid. Sulfate is reduced and large amounts of hydrogen sulfide are generated in this process. The black sediments of aquatic habitats that smell of sulfide are due to the activities of these bacteria. The black coloration is caused by the formation of metal sulfides, primarily iron sulfide. These bacteria are especially important in marine habitats because of the high concentrations of sulfate that exists there. 

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