Of particular interest to the scientific community is the possible existence of extraterrestrial biological activity due to the presence of liquid water under the icy surface. This search is motivated by analogy with anaerobic life found in abundance in under sea volcanic vents on Earth (McCollom 1999; Pappalardo et al., 1999) and the dry valley lakes of Antarctica. If Europa does indeed have a liquid water ocean beneath the outer ice crust as a result of interior volcanic heating, then it is possible that hydrothermal vents located on the seafloor may provide the necessary conditions for simple ecosystems to exist. The water ejected from the hydrothermal vents is typically rich in sulfur and other minerals. Bacteria present in the water extract all nutrients directly from the sulfur via chemosynthesis, making sunlight and oxygen unnecessary. Geochemical models have been proposed to explore the possibility that lithoautotropic methanogenesis (CO2 + 4H2 = CH4 + 2H2O) could be a source of metabolically useful chemical energy for the production of biomass at putative Europan hydrothermal systems (McCollom, 1999; Delitsky and Lane, 1997). In the absence of oxygen, anaerobic decomposition takes place in these hydrothermal vents. As a result of putrefactive breakdown of organic material (proteins), some elements are produced, such as hydrogen sulfide, methane, ammonia, and mercaptans, which are thiols/thio alcohols (RS-H, R-paraffinic, aromatic or cyclopraffine group). The sulfur in mercaptans found in bacteria ultimately derives from sulfate (-SO2- 4), which is reduced in the cell. In bacteria that utilize sulfate as a source of sulfur, several steps in the reduction process eventually lead to hydrogen sulfide (H2S) which is a direct precursor of the amino acid cysteine which is a thiol! The original source of sulphur on the Europan surface may be either: (a) ions implanted from the Jovian plasma, or alternatively, (b) much of the sulphurous material may be endogenic.