No. 80: Mar-Apr 1992
The preceding discussion of life's origin at hydrothermal vents was penned by an oceanographer. Astronomers, it seems, prefer different scenarios. C. Chyba and C. Sagan, in a major review article in Nature, see a two-fold problem: (1) identifying the source of the raw materials; and (2) identifying the source(s) of energy required for the synthesis of complex organic chemicals. First, they point to the steady drizzle of tiny, organic-rich particles drifting down to earth from cometary debris. These particles, which even carry spacesynthesized amino acids down to the earth's surface, seem likely chemical precursors of life. However, the atmosphere is also a potential source of prebiotic chemicals -- providing energy sources are available. Chyba and Sagan suggest as sources: lightning, ultraviolet radiation, and the shock energy derived from meteorite/asteroid/comet impacts. Together these energy sources, especially ultraviolet light, might synthesize thousands of tons of complex organic compounds each year.
(Chyba, Christopher, and Sagan, Carl; "Endogenous Production, Exogenous Delivery and Impact-Shock Synthesis of Organic Molecules: An Inventory for the Origins of Life," Nature, 355:125, 1992. Also: Henbest, Nigel; "Organic Molecules from Space Rained Down on Early Earth," New Scientist, 2. 27, January 25, 1992.)
Comment. Little is said in either of the above articles about the nature of and impetus for that final elusive step from organic chemicals to the simplest life forms. Everyone assumes that it happened, but did it? One can always imagine a universe in which matter, energy, and life have always existed.