Even the first protagonists of chemical evolution were aware of the fact that the composition of the early atmosphere had a strong influence on the probability that the biomolecules needed for an evolution of the first cell would be formed. Quite early, i.e., before 1950, two schools of thought are existed. Firstly, there were the advocates of an oxidizing or at least neutral atmosphere, who considered CO2 and CO as the primary source of carbon compounds and N2 as the only source of nitrogen containing organic compounds. Secondly, there were advocates of a reducing atmosphere mainly containing H2, CH4 as source of carbon, and NH3 as source of nitrogen compounds. The first comments on the early atmosphere came from geologists without direct connection to the hypothesis of chemical evolution. However, with the first two protagonists of chemical evolution, A. I. Oparin (1924, 1938, 1957, 1961) and J. B. S. Haldane (1929), representatives of both opposite directions of thoughts appeared on the scene.