The simplest of the cells, and also the first types of cells to evolve about 4.5 billion years ago, are the prokaryote cells, cells that lack a membrane. The bacteria are the best know example of prokaryote cells, but recently a new type of prokaryote cell was discovered called archea.

             Prokaryotic cells were the only form of life on earth for about 2 billion years. Fossils of prokaryotes were found in Western Australia and South Africa and have been dated as being about 3.5 billion years old. The chemical composition of the rock they were found, and nature of the rocks suggests that lithotrophic and fermentative modes of metabolism involved in early prokaryotes. Photosynthesis in prokaryote cells seems to have developed at least 3billionyears ago. The prokaryotic cells first developed Anoxygenic photosynthesis and oxygenic photosynthesis proceeded later. Larger more complicated prokaryote cells did not develop until around1.5 billion years ago.

             Prokaryotic cells differ largely from eucaryotic cells because eucaryotic cells contain a membrane-enclosed nucleus and several of other membranous organelles. Prokaryote cells do not develop into multicellular organisms like some plants and animals. .

             Prokaryotes are the smallest and least complex of all cells. Most prokaryote cells are small in size compares to the size of eucatyootic cells. The typical prokaryote measures about 10 to100 micrometers in diameter. Eucaryote cells have much greater volume of cytoplasm compared to its surface area, where the typical prokaryote cell is only about the size of the mitochondria of a Eucaryote cell. It is suspected that prokaryote cells are the mast abundant form of life on earth, both in terms of biomass and also number of various species. In the sea prokaryotes make up about 90% of all of the combined weight of all the organisms. There are about 1,500 distinct species of prokaryotic cells are known to man, but this number is probably only about 1% of all the suspected species in nature.