Molten Earth and the Origin of Prebiological Molecules

Abstract

Evidence for the molten Earth at its accretion time has been accumulated through the geochemical investigations and the observations of the surfaces of planets by space probes such as Venera 8, Mariner 9, Surveyor, Luna, and Apollo. The primitive terrestrial atmosphere might have been derived from the volcanic gases, as suggested by Rubey, but of a higher temperature than so far assumed. A thermochemical calculation of the composition of the volcanic gas suggests the following possibilities:

• (1) Large amounts of H₂ and CO were present in the primitive atmosphere. This gives a theoretical basis for the HCN-production experiment by Abelson.

• (2) HCHO and NH₃ existed in the primitive oceans, of the amount comparable with the weight of the present biosphere.

• (3) Plenty of NO ^-₃ , SO ^--₄ and PO ^---₄ were expected in the primitive oceans. The NO ^-₃ ions might have been useful for the nitrate respiration advocated by Egami.

In an appendix, it is argued, on the basis of the observational evidence of the exospheric temperatures of planets by space probes, that a highly reducing atmosphere would (if it existed on the primitive Earth) have disappeared very quickly due to the thermal escape of hydrogen from its exosphere.