Alkanes: Sources and Relevance
Alkanes: Natural Products
Alkanes are widespread in nature, originating mostly from biological processes. For example, odd-numbered, unbranched alkanes can be found in the spores of fungi while even-numbered alkanes are contained in sedimentary rocks. A theory stating that large amounts of methane found on Earth and Jupiter are of non-biogenic origin has not been proven as yet.
In nature, methane is mostly produced by bacteria, for example in the intestines of cows and pigs. Additionally, the simplest alkane is also produced by bacteria in wetlands, thus for a long time giving it the name marsh gas . It also exists in coal mines (mine gas) and because of the very explosive nature of an air and methane mixture it is responsible for mine gas explosions. The output of methane has doubled in the last hundred years making it one of the most important greenhouse gases which are responsible for global warming.
Presumably, methane played an essential role in the origin of life on earth. Methane and ammonia were the main components of the primordial atmosphere. Under the influence of UV irradiation, they form hydrogen cyanide (HCN) which subsequently could polymerize to adenine, an important building block of ribonucleic acid. Reaction of methane and ammonia in the presence of water leads to amino acids.
Some microorganisms, e.g. fungi, can metabolize alkanes. These microorganisms become increasingly important as a resource for degrading polluted soil caused by crude oil spills, i.e. the spoiled soil does not have to be removed and deposited elsewhere.