If one assumes that life originated on Earth, then this happened about 4.0 - 3.5 billion years ago. The oldest known fossils of living organisms are about 3.5 billion years old. Nothing is known about the very first living systems and their precursor structures. It is, however, generally accepted that one important characteristic property of all living systems is the presence of compartments. There is no life today without cellular compartments, which allow a separation of an internal organization from the environment.

Lipid vesicles - resembling the basic structure of the lipid matrix of contemporary biological membranes - are currently considered as reasonable models for the precursors of the first living systems. Lipid vesicles - also called liposomes or simply vesicles - are formed in aqueous solution upon dispersing a bilayer-forming amphiphile (often just called lipid); they are spherical structures containing an aqueous interior and one (or several) closed lipid bilayers which represent the boundary of the vesicles. The diameter of vesicles can vary between about 20 nm and 0.1 mm or more, covering the sizes of biological cells. Vesicles form from contemporary phospholipids present in biomembranes, such as phosphatidylcholine, or from mixtures of as simple chemical substances as linear fatty acids and the corresponding carboxylates. In this latter case, the kinetics of vesicle formation, vesicle growth and reproduction has been studied, in particular using cis-9-octadecenoic acid and cis-octadecenoate (oleic acid and oleate). Vesicles composed of oleic acid and oleate can be prepared directly from oleate micelles or from oleic anhydride through an alkaline hydrolysis, a process which is autocatalytic and leads to vesicle formation, growth and reproduction.

References:
Walde P., Wick R., Fresta M., Mangone A., Luisi P. L. (1994) J. Am. Chem. Soc. 116, 11649.
Blochliger E., Blocher M., Walde P., Luisi P. L. (1998) J. Phys. Chem. B, 102, 10383.