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Forming Polymers: A Problem for the Origin of Life

Walter Bradley
Casey Luskin
Photo: Hydrothermal vents, by NOAA, Public domain, via Wikimedia Commons.

Editor’s note: We are delighted to present a series by Walter Bradley and Casey Luskin on the question, “Did Life First Arise by Purely Natural Means?” This is the fourth entry in the series, a modified excerpt from the recent book The Comprehensive Guide to Science and Faith: Exploring the Ultimate Questions About Life and the CosmosFind the full series so far here.

Assume for a moment that there was some way to produce simple organic molecules on the early Earth. Perhaps these molecules did form a primordial soup, or perhaps they arose near some high-energy hydrothermal vent. Either way, origin-of-life theorists must then explain how amino acids or other key organic molecules linked up to form long chains (polymers), thereby forming proteins or RNA through a process called polymerization

A Popular Model

A problem for the primordial soup version of this model is that it would be at chemical equilibrium, without any free energy for organic monomers to react further.1 Indeed, chemically speaking, the last place you would want to link amino acids or other monomers into chains would be a vast, water-based environment like the primordial soup or in the ocean near a hydrothermal vent. As the U.S. National Academy of Sciences acknowledges, “Two amino acids do not spontaneously join in water. Rather, the opposite reaction is thermodynamically favored.”2 Origin-of-life theorists Stanley Miller and Jeffrey Bada similarly acknowledged that the polymerization of amino acids into peptides “is unfavorable in the presence of liquid water at all temperatures.”3 In other words, water breaks protein chains of monomers back down into amino acids (or other constituents), making it very difficult to produce proteins (or other polymers like RNA) in the primordial soup or underwater near a hydrothermal vent. 

The hydrothermal vent model is popular among origin-of-life theorists because it represents a high-energy environment, but this model faces additional problems. Hydrothermal vents tend to be short-lived, lasting perhaps only hundreds of years4 — timescales so short that the origin of life at undersea vents has been said to be “essentially akin to spontaneous generation.”5 It is also difficult to envision how prebiotic chemicals could become concentrated in such a chaotic, unbounded oceanic environment.6

The Biggest Obstacle

But perhaps the biggest obstacle to the origin of life at hydrothermal vents is implied in their name: extremely high temperatures. According to Scientific American, experiments by Miller and Bada on the durability of prebiotic compounds near vents showed that the superheated water would “destroy rather than create complex organic compounds.”7

In the view of Miller and Bada, “organic synthesis would not occur in hydrothermal vent waters,” indicating that vents are not an option for the origin of life because “[a]ny origin-of-life theory that proposes conditions of temperature and time inconsistent with the stability of the compounds involved can be dismissed solely on that basis.”8 Some might reply that certain alkaline thermal vents have lower temperatures,9 but the high pH present near alkaline vents tend to precipitate carbon into carbonate minerals, with very little carbon remaining in the seawater for prebiotic chemical reactions,10 and such a high pH is highly destructive to RNA.11 As one paper put it, “the evolution of RNA is unlikely to have occurred in the vicinity of an alkaline deep-sea hydrothermal vent.”12

Next, “The ‘Clumping’ Problem and the Origin of Life.”

Notes

  1. Nick Lane, John F. Allen, and William Martin, “How did LUCA make a living? Chemiosmosis in the origin of life,” BioEssays 2 (2010), 271-280.
  2. Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life, National Research Council, The Limits of Organic Life in Planetary Systems (Washington, DC: National Academy Press, 2007), 60.
  3. Stanley Miller and Jeffrey Bada, “Submarine hot springs and the origin of life,” Nature 334 (August 18, 1988), 609-611.
  4. John Horgan, “In the Beginning,” Scientific American 264 (February 1991), 116-125. Horgan is discussing the research of Miller and Bada in Miller and Bada, “Submarine hot springs and the origin of life.” 
  5. Jeffrey L. Bada, “New insights into prebiotic chemistry from Stanley Miller’s spark discharge experiments,” Chemical Society Review 42 (2013), 2186-2196.
  6. Koichiro Matsuno and Eiichi Imai, “Hydrothermal Vent Origin of Life Models,” Encyclopedia of Astrobiology, eds. Gargaud M. et al. (Berlin, Germany: Springer, 2015), 1162-1166.
  7. Horgan, “In the Beginning.”
  8. Miller and Bada, “Submarine hot springs and the origin of life.” See also Stanley L. Miller and Antonio Lazcano, “The Origin of Life Did It Occur at High Temperatures?,” Journal of Molecular Evolution 41 (1995), 689-692.
  9. Matsuno and Imai, “Hydrothermal Vent Origin of Life Models”; Deborah S. Kelley et al., “An off-axis hydrothermal vent field near the Mid-Atlantic Ridge at 30°N,” Nature 412 (July 12, 2001), 145-149; Deborah S. Kelley et al., “A Serpentinite-Hosted Ecosystem: The Lost City Hydrothermal Field,” Science 307 (March 4, 2005), 1428-1434.
  10. Norio Kitadai and Shigenori Maruyama, “Origins of building blocks of life: A review,” Geoscience Frontiers 9 (2018), 1117-1153.
  11. Harold S. Bernhardt and Warren P. Tate, “Primordial soup or vinaigrette: did the RNA world evolve at acidic pH?,” Biology Direct 7 (2012), 4.
  12. Bernhardt and Tate, “Primordial soup or vinaigrette?”

Walter Bradley

Fellow, Center for Science and Culture
Walter L. Bradley received his B.S. degree in Engineering Science (Physics) in 1965 and his Ph.D. in Materials Science and Engineering in 1968, both from the University of Texas (Austin).  He subsequently taught at the Colorado School of Mines, Texas A&M University as Full Professor of Mechanical Engineering, and for 10 years at Baylor University as a Distinguished Professor. His research area has been Materials Science and Engineering, with a focus on the mechanical properties of plastics and polymeric (plastic) composite materials, fracture and life prediction. He has received more than $7 million in research funding and published more than 150 refereed technical papers and book chapters.  He has been honored by the American Society for Materials and the Society of Plastics Engineers as Educator of the Year. His most recent work has focused on converting agricultural waste into functional fillers for engineering plastics to provide new economic opportunities for poor farmers in developing countries.

Casey Luskin

Associate Director, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.

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amino acidsFirst Life from Purely Natural Means? (series)hydrothermal ventsJeffrey Badaoceanorganic synthesisorigin of lifepolymerizationpolymersprimordial soupproteinsRNAScientific Americanseawaterspontaneous generationStanley MillertemperatureTIME