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A Science Odyssey
People and Discoveries

Amino acids are created in laboratory

Photo: Stanely Miller in lab

In 1929 British biochemist John Haldane (1892-1964) put forth the theory that the early atmosphere of Earth contained no free oxygen. Haldane and Soviet biochemist Aleksander Oparin (1894-1980) had both suggested that all the ingredients for life existed on Earth from the beginning and that energy from the sun and some unknown process had gotten life started.

In 1952 American chemist Harold C. Urey (1893-1981) published an elaboration of Haldane's theory, suggesting that Earth had formed from a cold stellar dust cloud. Its early atmosphere was then roughly similar to that of the rest of the universe -- that is, mostly hydrogen with traces of other elements. Urey figured that the trace oxygen, nitrogen, and carbon would be bound with hydrogen and exist as water, ammonia, and methane. With so much hydrogen around, free oxygen could not exist (it would always get bound up with hydrogen and form water). But as time went by (lots of time), many of the extremely light hydrogen atoms escaped into outer space until the balance changed. Without an excess of hydrogen, free oxygen could exist and gradually accumulate in Earth's atmosphere.

Stanley Miller (b. 1930) was a doctoral student working with Urey at the University of Chicago, researching possible environments of early Earth. In 1953 he combined the ideas of Urey and Oparin in a short, simple experiment.

He reproduced the early atmosphere of Earth that Urey proposed by creating a chamber with only hydrogen, water, methane, and ammonia. To speed up "geologic time" in his experiment, he boiled the water and instead of exposing the mix to ultraviolet light he used an electric discharge something like lightning. After just a week, Miller had a residue of compounds settled in his system. He analyzed them and the results were electrifying: Organic compounds had been formed, most notably some of the "building blocks of life," amino acids. Amino acids are necessary to form proteins which themselves form the structure of cells and play important roles in the biochemical reactions life requires. Miller found the amino acids glycine, alanine, aspartic and glutamic acid, and others. Fifteen percent of the carbon from the methane had been combined into organic compounds. As amazing as discovering amino acids at all was how easily they had formed.

That same year, the structure of DNA was elucidated, revealing even more strikingly the crucial role of very basic organic compounds. It also revealed a way in which some compounds -- nucleic acids -- could replicate and keep life going. The base pairs within DNA, which actually transfer the genetic code, are made of simple nitrogen-based compounds. Later researchers using techniques like Miller's were able to synthesize many of the components of DNA from gases thought to be present in the early atmosphere. In 1960 Juan Oró synthesized adenine, one of DNA's four bases and also a key component of ATP (adenosine triphosphate), an energy-carrier in cell respiration.

Miller's work showed that compounds necessary for life could have been formed in an environment without free oxygen, confirming Haldane's theory. The creation of amino acids from Earth's raw materials may well have been the first step of evolution. It also opens the possibility (since the proposed atmosphere was based on proportions of elements in the universe) that similar atoms and amino acids could have formed elsewhere, on planets formed in the same manner as Earth.

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