Carbon monoxide (CO), a toxic gas that quickly causes death, is the ironic focus of a recent attempt by some researchers to resuscitate ailing naturalistic explanations for life’s origin. However, at the latest pulse check, that attempt appears vain.
Textbook origin-of-life scenarios suggest that chemical reactions in early Earth’s atmosphere produced small organic molecules (prebiotic compounds) that accumulated in Earth’s oceans to form the famed “primordial soup.” Within the soup, prebiotic compounds hypothetically reacted to generate life’s building blocks—key steps in the origin-of-life pathway.
Impetus for this idea came from the legendary spark-discharge experiments first conducted by Stanley L. Miller in the 1950s. This twenty-two-year-old graduate student ostensibly showed that energy discharges passing through early Earth’s atmosphere could have sparked the formation of amino acids and other organic compounds. Miller’s experiments launched countless prebiotic simulation experiments all seeming to indicate that life’s building blocks could form in a primordial soup.
Few textbooks as yet acknowledge, however, that most origin-of-life researchers now consider Miller’s experiments irrelevant. The consensus view of atmospheric constituents has changed since the 1950s. Then they were thought to be hydrogen, methane, ammonia, and water vapor. Now, scientists believe early Earth’s atmosphere was composed of carbon dioxide, nitrogen, and water. This gas mixture does not yield organic compounds in prebiotic simulation experiments (hence, no primordial soup)—a devastating blow for the naturalistic origin-of-life scenario.
In response to this blow, Miller and collaborators recently appealed to CO-based atmospheres as a possible matrix for the production of prebiotic materials. According to this alternative scenario, CO, not carbon dioxide, was present in the primordial atmosphere. Miller and his team maintain that if early Earth’s crust were in a more reduced state than today, and if cool temperatures prevailed on the planet’s surface, their scenario makes sense. These researchers also think that comets may have delivered CO to early Earth.
Miller’s team showed that gas mixtures comprised of CO, nitrogen, and water do produce organic compounds, including amino acids, when bombarded with high-energy protons (a component of cosmic rays). On the surface, this finding seems to indicate that if CO were present in the primordial atmosphere, cosmic rays could have stimulated the production of primordial soup ingredients.
However, no evidence exists to indicate that CO was ever present in the primitive atmosphere. Even if CO were introduced through cometary delivery or through the outgassing of the crust, Earth’s water vapor would have removed it. Further, the flux of cosmic rays to the Earth (necessary to break apart CO’s highly stable chemical bond) is insufficient to produce the levels of prebiotic materials necessary to keep up with their subsequent chemical decomposition in any primordial soup.
Despite such extensive and intensive efforts, origin-of-life researchers have again (and consistently) failed to identify relevant sources for prebiotic compounds. Without prebiotic materials, there can be no primordial soup, and without a primordial soup, naturalistic origin-of-life scenarios remain “dead in the water.”
 Stanley L. Miller, “A Production of Amino Acids under Possible Primitive Earth Conditions,” Science 117 (1953), 528-29; Stanley L. Miller, “Production of Some Organic Compounds Under Possible Primitive Earth Conditions,” Journal of American Chemical Society 77 (1955): 2351-66.
 François Raulin, “Atmospheric Prebiotic Synthesis,” presentation at the 12th International Conference on the Origin of Life and the 9th meeting of the International Conference on the Origin of Life, San Diego, CA 1999; Stanley L. Miller, “The Endogenous Synthesis of Organic Compounds,” The Molecular Origins of Life: Assembling Pieces of the Puzzle, ed. André Brack (New York: Cambridge University Press, 1998), 59-85.