26. Origin of Life on Earth   Previous PageNext Page
       The Drama of Life

3. Volcanic outgassing from the interior created a new atmosphere for the planet, made up of reduced compounds: H2, CH4, N2, NH3, H2O, and H2S. In the absence of today's high-altitude ozone shield, ultraviolet radiation from the sun penetrated all the way to the surface of the Earth. This radiation, lightning discharges, volcanic heat, and natural radioactivity all provided energy sources for the spontaneous reaction of the atmospheric gases to form more complex molecules: HCN and aldehydes, nitriles, organic acids and bases, simple carbohydrates and amino acids. These were leached into the oceans by rain, where they slowly built up a thin "Haldane soup", which was stable for long periods of time in a reducing atmosphere.

4. Life evolved from this soup, perhaps through intermediate stages of localized but nonreproducing chemical systems, protected by simple barrier membranes. Catalytic proteins, or crude enzymes, developed from random polymers of amino acids, sometimes in association with metal ions and organic molecules. Energy for chemical syntheses was provided by the breakdown of polyphosphates, or later by molecules such as ATP, both formed originally by nonbiological means. As competition depleted the natural supply of many necessary substances in their surroundings, the more successful "protobionts" developed the ability to synthesize these substances from more plentiful molecules. Those primitive chemical systems that also developed a machinery for duplicating all of this chemistry in daughter systems, crossed the threshold of what we would define as life. The primitive information-transfer system need have borne little resemblance to the elaborate DNA-RNA-ribosome system of today, but the function would have been the same.

5. As the natural supply of polyphosphates and ATP ran short, some protocells evolved glycolysis as a means of degrading organic molecules and saving the energy as homemade ATP. This pattern of metabolism became so advantageous that only those organisms that possessed it survived to the present. Glycolysis and gluconeogenesis developed, with the necessary enzymes floating freely in the cell fluid. The stage of the fermenting bacteria was reached. Even with this metabolic capability, the amount of life on the planet was strictly limited by the available supply of nonbiologically produced organic molecules for use as energy sources.

  Page 31 of 36 HomeGlossary