In the previous chapter it was determined that the current chloroplasts (as endosymbiotic organelles of eukaryotic cells) have their origin in free prokaryotes possess DNA, ribosomes and double membrane. Therefore the question is about the origin of these free prokaryotes able to produce organic matter and oxygen for later use by the mitochondria.

Until 1977 it was assumed that the inhabitants of the seabed were nourished by the organic matter from the surface and therefore all organisms had its origin into beings of the earth's surface.

However the discovery of submarine hydrothermal black smokers allowed to propose other options to be isolated into the depths, organisms with photosynthetic capabilities and others with chemo synthetic capabilities.

Both could be the source of free prokaryotic chloroplast.

Although at first it was thought that chemosynthetic organisms could be pre-photosynthetic, studying their current metabolic mechanisms that fact becomes unlikely as to get the energy it needs the oxygen dissolved in the water, later development, by the reaction 4SH2+CO2+O2=CH20+4S+3H20.

Similarly considering that the first organisms from the depths were photosynthetic we are in a difficult situation as the current representatives, For example Chroloflexus auricantiacus of Chloroflexaciae family can use the light energy emitted by the black smokers but perform an anoxygenic photosynthesis using SH2 as electron donor by reacting 2SH2+CO2=CH20+2S+H20.

Thus we face the possibility that the original free prokaryotes chloroplasts proceed somehow more primitive form that used the photosynthetic energy such as anoxygenic (it uses light energy of wavelength close to red 700 nm from heat sources) and through this possibility, we might call the methylenic route produce methylene and oxygen. This route would use the inorganic carbon by the reaction:

(1) 4C+ 2SH2+ 2H20= 4CH2+2S+02 leading to formation of oxygen in the depths and perhaps the first carbohydrate (6CH2 + 302 = C6H1206) similar to those produced by the chlorophyll function but with a lower yield in the production of free oxygen.

This pre-chloroplast form of low performance could evolve into a oxygenic route using energy wavelength of 680 nm or less, from sunlight, and carbon dioxide instead of inorganic carbon (2) 6CO2 + 6H20 = C6H1206 +602.