Margaret Oakley Dayhoff -- Thermodynamics of Planetary Atmospheres
| In the early 1960s, Dr. Dayhoff collaborated with EllisLippincott and Carl Sagan, among others, to develop thermodynamic modelsof cosmo-chemical systems, including prebiological planetary atmospheres. She used a computer to model atmospheric conditions and composition on various planets under different conditions. 燭o do this, she developed a computer program that calculated equilibrium concentrations of gases in a planetary atmosphere. The particular compounds and elements to be considered could be chosen each time the program was run. The result was a highly versatile program that could be used to model the background or average atmospheres of Venus, Jupiter and Mars. In addition, it could model the present-day andprimordial terrestrial atmosphere. In her study of the primordial terrestrial atmosphere, Dr. Dayhoff showed that long -chain hydrocarbons (oils)would form naturally under reducing conditions. As the oxygen content ofthe atmosphere increased, a sharp cut-off point would be expected, after whichsuch natural formation of oils would abruptly cease. The abundance of oilin the earth's crust may be explained in part by such formation of hydrocarbonsbefore the oxygen content of the atmosphere passed the cut-off point. |  ? |
| C-H-O ternary diagram for the atmosphere of Mars. | |
Dr. Dayhoff was especially interested in whether a primordial atmosphere at thermodynamic equilibrium might have contained compounds necessary for the formation of life. She found that numerous small biologically important compounds can appear with nospecial equilibrium mechanism to explain their presence. On the other hand,there are compounds that are critical to life, such as ribose, adenine andcytosine, which are extremely scarce in the equilibrium situation. | |