300 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1964 



metabolism of the cell. In this way, the nucleic acids control the 

 form and functions of all cells. 



With geological time available for the origin of life, the key event 

 may then have been the spontaneous production of nucleoside phos- 

 phates in the primitive environment. In contemporary cells, these 

 building blocks join together in the presence of special enzymes which 

 speed their rate of reaction ; but given enough time, it is possible that 

 nucleoside phosphates will spontaneously polymerize to nucleic acids. 



How might such nucleoside phosphates have originated, billions of 

 years ago, on the primitive Earth ? There are very good reasons for 

 believing that the primitive atmosphere of the Earth contained large 

 amounts of hydrogen, the most abundant element in the universe. 

 Some 4 billion years ago, the atmosphere should have consisted pri- 

 marily of hydrogen and the hydrogen-rich gases methane, ammonia, 

 and water. The transition from this primitive atmosphere to our 

 present oxidizing one is due in part to the escape of hydrogen into 

 interplanetary space, and in part to the production of oxygen by 

 plant photosynthesis. In 1953, Stanley Miller and Harold Urey 

 applied an electric spark — lightning on a smaller scale — to a mixture 

 of gases resembling the primitive atmosphere of the Earth. They 

 produced a variety of amino acids, the building blocks of proteins. 

 Since these pioneering experiments, other scientists have produced 

 other organic molecules — cyanides, aldehydes, hydrocarbons — in simu- 

 lated primitive atmospheres. In addition to electrical discharges, 

 other energy sources available on the early Earth, such as ultraviolet 

 light and high temperatures, have been utilized. 



In later experiments, the amino acids and other simple products 

 have themselves been used as starting points in the production of 

 more complex organic molecules — polypeptides, resembling simple 

 proteins ; sugars ; and the kinds of bases found in nucleosides. It is 

 a curious fact that these bases absorb ultraviolet light at just those 

 wavelengths transmitted, in the absence of ozone, by the primitive 

 terrestrial atmosphere. For this reason, Cyril Ponnamperuma, Euth 

 Mariner, and I last year irradiated dilute solutions of bases, sugars, 

 and phosphorus compounds, and found that we had made in high yield 

 various nucleosides and nucleoside phosphates. One of these was 

 adenosine triphosphate (ATP). It is not only the most important 

 energy-storage molecule in plants and animals; ATP is also an RNA 

 precursor, and differs in only one atom from an important building 

 block of DNA. From experiments such as these, it can be estimated 

 that the amount of organic matter produced from natural energy 

 sources in early times is so large that, if dissolved in the present 

 oceans, it would make about a 1 percent organic solution. 



Here, then, is a picture of the early stages of the origin of life. 

 Ultraviolet light, lightning, or other forms of energy produce sugars 



