Environmental conditions surrounding the origin and early Archean evolution of life: A hypothesis

Abstract

The supposition that free oxygen was absent from the Earth's early atmosphere may be questioned. The paradoxes raised for the prebiotic formation of early peptides, proteins and nucleic acids by the absence of oxygen (UV-destruction) and the presence of oceans (spontaneous hydrolysis) are difficult to resolve and are usually ignored. An alternative hypothesis may be entertained that the primitive Earth lacked an early condensed ocean of water and was surrounded instead by a moist greenhouse atmosphere capable of providing the small amounts of photolytic oxygen necessary for a UV-protective ozone screen. These conditions favor the hydration—dehydration cycles needed for complex organic polymerizations, while they minimize the problem of UV-destruction. Simpler prebiotic starting materials can be derived from carbonaceous chondrites (or comets) rather than from terrestrial atmospheric reactions.