Chognogeny (Nature of primitive life and its Evolution)continued selection of more successful eobionts accompanied with the formation of first cell. Earliest cells were called anaerobic prokaryotic, & chemo heterotrophic.
They derive nutrition (organic compound) from Seas. So these cells grew to enormous size. To restrict their size chemoheterotrophs started cell mitosis and so increased their number. Some of chemoheterotrophs shows modification to form chemoautotroph. These started to synthesizing their own organic food from inorganic Compounds in presence of chemical energy and enzymes e.g. sulphate Reducing bacteria etc. Main force for this kind of evolution was proposed to be of mutation.
First photoautotrophs were anoxygenc as these did not use water as a raw Material in photosynthesis. Later these developed true chlorophyll & started using the water as a reagent so O2 was evolved in process Of photosynthesis.
First oxygenic and aerobic photoautotrophic were the cyanobacteria that believed to evolve about 3500 million years ago. Only forms of life on the earth were bacteria, moulds and cyanobacteria. Gradually blue green algae evolved into other forms of algae. It is Estimated that eukaryotes developed around 1600 million years back, they evolved from either mutation in prokaryotes or symbiotic association of different prokaryotes. Later many algae protozoans and other living Organisms were developed.