origin of cell membranes
Cell membrane formation was a crucial stage in the evolution of terrestrial life. However, whether the first self-replicating life-forms on Earth possessed a membrane or whether they were merely naked strands of nucleic acid is as yet undetermined. Even if the earliest organisms did possess a membrane of some sort, it was probably not of their own making. The likelihood is that ready-made receptacles were to hand which they could have used. Such receptacles may form in interstellar space on the surface of cosmic dust grains. At least two pieces of evidence support this view: (1) the discovery of what appear to be two-layered vesicles in material extracted from the Murchison meteorite (see organic matter, in meteorites); and (2) the synthesis of similar microscopic structures on Earth in experiments designed to replicate conditions within interstellar clouds of gas and dust.