Spontaneously form membranes when mixed in water and most likely were one of the first organic compounds formed on earth?

phospholipids

Explanation:

As regards the lipid membrane of the first protocells, it is most likely that it initially consisted of simpler fatty acids than the phospholipids that make up the current membranes (see appendix). If the modern membranes are bilayers of glycerol phospholipids, the primitive membranes would probably be made up of simpler, single-chain molecules, also amphiphilic in nature (with a soluble part and another insoluble in water), such as monocarboxylic acids or alcohols. The origin of these compounds could be multiple. On the one hand, it has been seen that they are very abundant in meteorites of the type of carbonaceous chondrites, so they could have arrived on Earth already formed from outer space. But it is also possible that they were formed abioticly on the primitive Earth by the reaction of CO and hydrogen to give rise to various hydrocarbons, a reaction that would be viable at high temperatures in the presence of ferric catalysts, on the surface of montmorillonite clays and also in hydrothermal conditions. Regardless of the origin, the result would be the presence of fatty acids initially very diluted in an aqueous solution, but which would be concentrated by successive evaporation cycles, or by the formation of small aerosolized drops that would also transfer those vesicles to points distant from the place where The first organic membrane compounds that formed on Earth were formed and would be.