According to Oparin, the atmosphere of primitive earth was reducing because H atoms were most numerous and most reactive. Large quantities of H2, N2, water vapour CO2,CH4 and NH3 were present, but free oxygen was not present in significant amount. Related Theory Oparin and Haldane suggested that life originated from non-living organic molecules like proteins and RNA. This was followed by the theory of chemical evolution which suggested that atmospheric conditions of earth led to the formation of organic molecules from inorganic molecules.