The earth of several billion years ago was a very different place than it is today, or so scientists who have studied the its past tell us. The atmosphere wasn't the same as it is today, and continents were still forming from the hot magma that underlies what we now experience as solid ground. Some scientists theorise that life had its beginnings in this chaotic environment, forming in warm ocean or lake water from a collection of chemicals they call the primordial soup. The theory has many detractors, but it has been successfully tested twice.
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The Primordial Soup Theory
For a time, scientists believed that earth's early atmosphere consisted of a number of hydrogen-based gases including methane and ammonia. When these gases were energised, possibly by lightning, cosmic radiation or shocks generated inside the earth, they formed complex chains of molecules called amino acids that dropped to earth with falling rain. When they collected in the hospitable environment of a suitable warm body of water, they formed the primordial soup in which they further combined to form proteins and finally rudimentary organisms. The primordial soup theory was first proposed in 1920 by A.I. Oparin, a Russian chemist, and J.B.S. Haldane, a British geneticist, who worked independently of each other.
Testing the Theory
In a experiment conducted in 1950, a physicist, Harold Urey, and a chemist, Stanley Miller, combined methane, ammonia and hydrogen gases with water and energised them with electricity. By doing so, they managed to produce amino acids. Later they discovered they could achieve similar results by energising the mixture with ultraviolet radiation, heat or a physical shock. Subsequent to the experiment, scientists became sceptical that the chemicals Miller and Urey used were present in earth's early atmosphere, so chemist Jeffrey Bada performed it again in 1983 with a different mixture and achieved similar results.
Problems with the Primordial Soup Theory
The primordial soup theory has many detractors in the scientific community, who oppose it for several reasons. They say the soup may have contained amino acids, but these molecules can combine in an enormous number of ways, and the probability that they would have formed into proteins is minuscule. Doing so, they say, violates the Second Law of Thermodynamics, which mandates increasing disorder and chaos in the universe. Moreover, the soup would have to have been in a very small body of water, or the mixture would be too diluted for the level of organisation required for life to form.
Scientists lost faith in the primordial soup theory until Urey's and Miller's results were replicated by Bada using a solution more likely to have existed in earth's early atmosphere. Many still prefer the idea that life was delivered to earth on a comet or meteorite. A laboratory for testing the theory may exist on Enceladus, one of the moons of Saturn. The Cassini spacecraft has photographed plumes of water vapour streaming from one of its poles, and some researchers believe conditions may exist inside the moon favourable for the formation of life according to the primordial soup theory. Further investigation may yield evidence to support or refute the theory.
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