For almost a century, popular thought has held the Primordial Soup theory as the most likely means for the generation of life. But as Yan Chen reports, a new recipe may prove more palatable.
Image credit: James W. Brown, NC State University
In 1871, Charles Darwin suggested the idea of a “warm little pond” as the origin of life in a letter to Sir Joseph Hooker. This formed the basis of the primordial soup theory model proposed by Haldane in 1929. He suggested that strong ultraviolet radiation gave energy to convert simple molecules such as water, methane, and ammonia into the first organic molecules. Due to a lack of living organisms at the start, the organic molecules started to accumulate. This increased the chances of the additions of all the organic molecules into larger molecules until RNA – a precursor of the genetic material DNA – molecules were formed. This theory was backed up by Peter Miller’s synthesis of organic molecules theory published in 1953. The supporters of this theory believed RNA is the first molecule produced after all the “soup” reactions. In this model, RNA acts as the only catalyst and the only replicator causing all the other biochemical reactions. It has been more than 80 years since the theory was first proposed. Is the theory still standing or is about to pass its expiry date?
In the primordial soup theory, there are a lot of descriptions of chemical reactions and absolutely no mention of the cell. Furthermore, it suggests a paradoxical source of energy. The primordial soup theory suggests the energy comes from the ionization of the UV light. However, light intense enough to initiate biochemical reactions would also have been deleterious, as seen in its carcinogenic properties. Therefore, it is too hard to believe that UV is the energy source and initiator to generate the first cell.
Bill Martin suggested archaea (single celled organisms that share a lot of traits with higher organisms) and bacteria are most likely to have descended from a common ancestor of all life after studying their evolutionary relationships. The common ancestor must have had a genetic code of the same sort as all existing organisms and a mechanism to convert it into useful molecules, which is also present in all modern life. Combined with a great collection of geological, geochemical and thermodynamic findings, an alternative model – alkaline hydrothermal vent system – was proposed by Russell in 1994. He pointed out the differences in acidity, temperature and redox potential (a measure of the tendency of a chemical species to acquire electrons) can provide the continuous energy needed for the chemical reactions in the origin of life. They suggested that a very common mineral found in the early sea floor – olivine – reacted with water to produce a warm, alkaline, hydrogen-rich solution that came up from the sea floor to produce the alkaline hydrothermal vent. Such an environment allowed the reactions leading to first cellular life by establishing the ionic and temperature gradient provided by a cell before cells had developed. Cellular life stemmed from this environment-differential as a means to drive metabolic and self-replicating reactions.
Martin and Russell have painted a great picture of the origin of life. There are still some gaps, but the evidence is certainly growing. It may be time to throw out the Primordial Soup.
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