4 He described an occupation hazard that manifested as a painful inflammation in the eye in workers who were chronically exposed to an unknown “acidic vapor” while cleaning privies and cesspits. In medicine, perhaps the earliest reference to H 2S, even before its identity was established, was in a 1713 publication titled De Morbis Artificum Diatribes (Disease of Workers) by the Italian physician, Bernardino Ramazzini. High levels of H 2S are lethal to most animals, but a few like pupfish, poeciliids, molluscs, and giant tubeworms are specialized to flourish in H 2S-rich habitats like marshes and deep-sea hydrothermal vents. Furthermore, green and purple sulfur bacteria use H 2S as an electron donor for photosynthetic CO 2 reduction. 3 In this organism, H 2S provides the reducing power for CO 2 fixation via the Calvin cycle. One of the first reported examples of lithothrophy, i.e., the ability to utilize inorganic substrates for energy generation, is of the H 2S-oxidizing bacterium Beggiatoa, discovered by Winogradsky. H 2S would have been useful for synthetic purposes but also as a source of metabolic energy.
2Įarly life forms likely thrived in an H 2S-rich environment. Furthermore, the conditions that produced nucleic acid precursors likely also created the starting materials for natural amino acids and lipids suggesting that a simple set of reactions could have given rise to most of life’s building blocks. 2 It is possible to create nucleic acid precursors on metal centers starting with hydrogen cyanide, H 2S, and ultraviolet light. 1 It is postulated that RNA, protein, and lipid precursors have common origins in a cyanosulfidic protometabolism. The recent discovery of unanalyzed samples from Miller’s 1958 experiment confirmed that sulfur-containing molecules (including the amino acids cysteine and methionine) could have been formed under the atmospheric conditions of early Earth from H 2S, which is released in volcanic emissions and from other geothermal activity. Hydrogen sulfide (H 2S) is inextricably tied to the emergence of life on Earth.