Atmospheric Production of Glycolaldehyde Under Hazy Prebiotic Conditions
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Atmospheric Production of Glycolaldehyde Under Hazy Prebiotic Conditions Chester E. Harman · James F. Kasting · Eric T. Wolf
Received: 20 February 2013 / Accepted: 11 April 2013 / Published online: 22 May 2013 © Springer Science+Business Media Dordrecht 2013
Abstract The early Earth’s atmosphere, with extremely low levels of molecular oxygen and an appreciable abiotic flux of methane, could have been a source of organic compounds necessary for prebiotic chemistry. Here, we investigate the formation of a key RNA precursor, glycolaldehyde (2-hydroxyacetaldehyde, or GA) using a 1-dimensional photochemical model. Maximum atmospheric production of GA occurs when the CH4 :CO2 ratio is close to 0.02. The total atmospheric production rate of GA remains small, only 1×107 mol yr−1 . Somewhat greater amounts of GA production, up to 2 × 108 mol yr−1 , could have been provided by the formose reaction or by direct delivery from space. Even with these additional production mechanisms, open ocean GA concentrations would have remained at or below ∼1 μM, much smaller than the 1–2 M concentrations required for prebiotic synthesis routes like those proposed by Powner et al. (Nature 459:239–242, 2009). Additional production or concentration mechanisms for GA, or alternative formation mechanisms for RNA, are needed, if this was indeed how life originated on the early Earth. Keywords Prebiotic · Atmosphere · Chemistry · Glycolaldehyde · Fractal haze
Electronic supplementary material The online version of this article (doi:10.1007/s11084-013-9332-7) contains supplementary material, which is available to authorized users. C. E. Harman (B) · J. F. Kasting Department of Geosciences, Penn State University, University Park, PA 16802, USA e-mail: [email protected] E. T. Wolf Laboratory for Atmospheric and Space Physics, Space Science Building (SPSC), University of Colorado, 3665 Discovery Drive, Boulder, CO 80303-7820, USA
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Introduction The difficulty of forming RNA prebiotically has long been one of the greatest stumbling blocks for theories of the origin of life. Spark discharge experiments (simulating lightning) have been used to generate amino acids (Miller 1953; Cleaves et al. 2008), RNA precursor species like peptide nucleic acid (PNA) (Nelson et al. 2000), some nucleobases, in conjunction with eutectic freezing (Menor-Salván et al. 2009), and have been conjectured to form sugars (Schlesinger and Miller 1983), while forming ribose prebiotically is challenging (Shapiro 1984, 1988). Furthermore, hooking ribose together with pyrimidine nucleobases has long been considered difficult or impossible (Szostak 2009). Recently, Powner et al. (2009) discovered a way around this last problem by way of a novel multi-step ribonucleotide synthesis mechanism that bypasses the need for free sugars and nucleobases. As starting materials, their mechanism requires cyanamide (CN2 H2 ), cyanoacetylene (C3 HN), glycoaldehyde (HOCH2 CHO), glyceraldehyde (C3 H6 O3 ), and inorganic phosphate. These compounds could conceivably have been b
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