In 1929, separately, two scientists, Alexander Oparin and John Haldane, published the same hypothesis (except for some details) on the origin of life. According to these scientists, upon Earth''s formation the atmosphere was essentially constituted by four gases: hydrogen, water vapor, ammonia and methane. These compounds would have reacted spontaneously and during these reactions the atoms of carbon, hydrogen, oxygen and nitrogen would have recombined to produce by abiotic synthesis the first organic compounds. The energy required for these reactions came from solar radiation (particularly ultraviolet), electrical discharges from lightnings, radiation, radioactive elements, heat from volcanic areas.
After forming in the early atmosphere, the first compounds would have been transported by rain into rivers, lakes and oceans and there accumulated in large quantities. Due to the high concentration, molecules would collide with each other originating spontaneous reactions. By molecular evolution or chemical evolution (the transformation of simple molecules into more complex ones), all kinds of organic molecules necessary to the emergence of life came to be.
Some of these molecules, which existed in what Haldane designated as "primordial soup", would have clustered spontaneously in small groups and isolated through a semipermeable membrane (which enabled the exchange of substances with the medium) resulting in pre-biological forms. In these forms there would have been chemical reactions important to life.
The pre-biological forms then would have originated more and more complex forms that would have been able to perform exchanges with the medium (most probably there would have formed glucose where they developed and the process from which they obtained energy would certainly have been fermentation, due to the absence of oxygen).
By evolution of pre-biological forms, would emerge the first life form: the cell - anaerobic bacteria, which fed on organic substances of abiotic origin in the medium.
Therefore, through biological evolution the first life forms increased their complexity originating autotrophic, eukaryotic and aerobic cells and through further evolution, originated the diversity of living beings that exist on Earth today.