Curiously, Miller and Orgel concede many of his points in their book either directly or indirectly. Both volumes discuss the composition of the primitive atmosphere as a key factor in any theory of the origin of life. Gish points out that the idea of a reducing atmosphere was developed by Oparin and Urey as a necessary condition for the formation of organic compounds needed for living things. Miller and Orgel are frank to admit the problems and their own preconceptions in this area. Geological and geophysical evidence is insufficient to allow us to state with any precision what conditions were like on the surface of the primitive earth.
Arguments concerning the composition of the primitive atmosphere are particularly controversial.
It is important, therefore, to state our own prejudice clearly. N 2 and H 2 O against the methane-ammonia atmosphere of Urey but points out further that there is little evidence that outgassing of the primitive earth would produce either type of atmosphere. Gish further cites work by Davidson and Brinkmann which suggests that the oxygen concentration in the earth's atmosphere would have reached an appreciable fraction of its present level very early in the earth's history. Miller and Orgel consider most of the same evidence but cling to their admitted prejudice that a reducing atmosphere must have been present long enough for the formation of compounds needed to begin life on the primitive earth. With this assumption, Miller and Orgel turn to a consideration of sources of energy and the nature of possible reactions involved in prebiotic syntheses.