In contemporary single celled organisms, the cell membrane forms a compartment which enables the organism to be separated from its environment and from other organisms. The mechanism by which early organims were separated from one another is an important issue for the origin of life. This need not necessarily have been by means of a membrane. For example, some theories suppose that early organisms could have been chemical systems adsorbed to the surface of minerals. They would have been separated from one another by virtue of occupying (more or less) fixed locations on the mineral surface.