Stanlley Miller

PERCEPTIONS OF SCIENCE

Prebiotic Soup—Revisiting the Miller Experiment
Jeffrey L. Bada and Antonio Lazcano

Fifty years ago, Science published a paper by a graduate student reporting the synthesis of amino acids under presumed primitive Earth conditions. This report started modern research on the origins of life.

ESSAY

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sn’t life wonderful?” sang Alma Cogan entists favored theidea of primordial be- organic compounds was not considered to and Les Howard in their almost forgotten ings endowed with a plant-like (autotroph- be a necessary prerequisite for the emer1953 hit. That same year, Stanley L. ic) metabolism that would allow them to gence of life. Miller raised the hopes of understanding use CO2 as their source of cellular carbon. From the 1950s, chemists were drawn theorigin of life when on 15 May, Science However, some scientists—including A. I. toward the origin of life. Driven by his inpublished his paper on the synthesis of Oparin, J. B. S. Haldane, C. B. Lipman, and terest in evolutionary biology, Melvin amino acids under conditions that simulat- R. B. Harvey—had different ideas (3). The Calvin tried to simulate the synthesis of ored primitive Earth’satmosphere (1). Miller most successful and best-known proposal ganic compounds under primitive Earth had applied an electric discharge to a mix- was that by Oparin, who, from a Darwinian conditions with high-energy radiation ture of CH4, NH3, H2O, and H2—believed analysis, proposed a series of events from sources. He and his group had limited sucat the time to be the atmospheric composi- thesynthesis and accumulation of organic cess: the irradiation of CO2 solutions with tion of early Earth. Surthe Crocker Laboratory’s prisingly, the products 60-inch cyclotron led only were not a random mixture to formic acid, albeit in of organic molecules, but fairly high yields (5). rather a relatively small Miller’s publication 2 number of biochemically years later showed how significant compounds suchcompounds of biochemias amino acids, hydroxy cal importance could be acids, and urea. With the produced in high yields publication of these drafrom a mixture of reduced matic results, the modern gases. era in the study of the oriThe origin of Miller’s gin of life began. experiment can be traced Since the late 19th cento 1950, when Nobel lautury, the belief in a natural reate Harold C. Urey, whoorigin of life had become Highlights in organic synthesis in conjunction with theories of the origin of life. had studied the origin of widespread. It was generalthe solar system and the ly accepted that life’s defining properties compounds to primordial life forms whose chemical events associated with this could be understood through physico-chemi- maintenance and reproduction depended process,began to consider the emergence cal characterization of “protoplasm,” a term on external sources of reduced carbon. of life in the context of his proposal of a The assumption of an abiotic origin of highly reducing terrestrial atmosphere. used to describe the viscous translucent colloid found in all living cells (2). Expressions organic compounds rested on firm grounds. Urey presented his ideas in alecture at the like “primordial protoplasmic globules” were In 1828, F. Wöhler had reported the first University of Chicago in 1951, followed by used not only by scientists but also in fiction, chemical synthesis of a simple organic the publication of a paper on Earth’s primfrom Gilbert and Sullivan’s Pooh-Bah in The molecule (urea) from inorganic starting itive atmosphere in the Proceedings of theMikado (1885) to Thomas Mann’s somber materials (silver cyanate and ammonium National Academy of Sciences (6). imaginary character Adrian Leverkühn in chloride). Almost a year and a half after Urey’s After a large body of research on the lecture, Miller, a graduate student in the Doktor Faustus (1947). But few dared to be explicit, even in novels. Questioned about the synthesis of simple...