 The S-layer, which is found in most Archaea, and in many bacteria, serves many crucial functions including protection from deleterious extracellular substances.The first S-layers were discovered in bacteria in the 1950s and the presence of S-layers in many Archaea was determined through microscopic (both light and electron) studies of Archaea.The presence of an S-layer in a member of the Methanosarcinales was determined in the 1980s by electron microscope (EM) studies examining the cell morphology of "Methanosarcina mazei".