Prebiotic synthesis of simple organic monomers

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Editor’s note: We are pleased to present a series by Walter Bradley and Casey Luskin on the question “Did life first arise by purely natural means?” This is the third entry in the series, and is a modified excerpt from the last book The Comprehensive Guide to Science and Faith: Exploring the Ultimate Questions about Life and the Universe. Find the full series so far here.

Miller-Urey experiments were conducted in 1952-19531 It was celebrated as a major advance in the search for a chemical pathway from the gases presumably in Earth’s early atmosphere to the chemical reactions that produced amino acids, the building blocks of protein molecules. This experiment (see apparatus described below), and other similar experiments, produced additional simple monomers – some of the building blocks of life.

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Miller-Urey reviews

Subsequently, careful criticism of Urey Miller Experiments and similar experiments have raised significant doubts about their significance, although they are still taught in some high school textbooks as if they were scientifically sound. The atmosphere used in their experiments assumed a primitive atmosphere very rich in energy from methane, ammonia, and hydrogen, none of which was chemically stable in Earth’s early atmosphere. NASA studies of Earth’s atmosphere as early as the 1980s confirmed that the mixture of atmospheric gases used in the pioneering Miller-Urey experiments was wrong. the magazine Sciences He summarized the discoveries in 1980 by noting, “There is no geological or geochemical evidence collected in the past 30 years favoring an energy-rich, strongly reducing primordial atmosphere (such as hydrogen, ammonia, and methane without oxygen). Only the success of Miller’s laboratory experiments is who recommends it.2 Subsequent articles described him equally frankly – in 1995, Sciences He stated that “the early atmosphere was nothing like Miller Urey’s situation”.3 Back in 2008, an article was published in Sciences She stated, “Geoscientists today suspect that the primordial atmosphere had the highly reductive composition that Miller used.”4

Early Earth’s Atmosphere

There are good reasons to understand why Earth’s early atmosphere did not contain high concentrations of methane, ammonia, or other reducing gases. Earth’s early atmosphere is believed to have resulted from the release of gases from volcanoes, and the formation of those volcanic gases is related to the chemical properties of the Earth’s inner mantle and core. Geochemical studies have found that the chemical properties of the Earth’s interior were very similar in the past as they are today.5 But today’s volcanic gases do not contain methane or ammonia, and generally no less. Instead, a carbon dioxide-dominated atmosphere is preferred, but this presents a problem for prebiotic synthesis experiments, as prominent origin of life researcher David Demmer noted: “CO2 does not support the rich set of synthetic pathways that lead to potential monomers, So the question arose again: What is the main source of organic carbon compounds?6

Another problem with Miller-Urey prebiotic synthesis experiments is that when amino acids are synthesized from energy-rich gases, a racemic amino acid mixture of 50 percent L-amino acids and 50 percent amino acids, sometimes called left And the Aimen. Protein molecules created in living systems must contain 100% of the L-amino acids. If there are any D-amino acids in the chain, this will prevent the amino acid chain from folding into the proper 3D protein structures attached to the amino acid chain, thus It prevents her from doing her job.

More problems with Miller Urey

There are several additional problems in Miller-Urey research that seeks to identify plausible chemical pathways for the synthesis of proteins, DNA and RNA molecules—the molecules of life. The evidence against prebiotic synthesis of the building blocks of life is so rigorous that in 1990, the National Research Council’s Council on Space Studies recommended “a re-examination of biomonomer synthesis under primitive Earth-like environments, as demonstrated by current models of early Earth.”7 Because of these difficulties, many leading theorists have abandoned the Miller-Urey experiment and the “primal soup” model it is claimed to support. In 2010, Nick Lane, a biochemist at University College London, stated that the primitive soup theory “does not hold water” and “has passed its expiration date.”8 Instead, it is suggested that life originated in hydrothermal vents under the sea where water circulates through hot volcanic rocks on the ocean floor. But both the hydrothermal hypothesis and the primordial soup hypothesis face another major problem.

next one“The Formation of Polymers: A Problem at the Origin of Life.”

Notes

  1. Stanley L. Miller, “Amino Acid Production Under Possible Primordial Earth Conditions,” Sciences 117 (May 15, 1953), 528-529.
  2. Richard A. Kerr, “The Origin of Life: Proposed New Components,” Sciences 210 (October 3, 1980), 42-43.
  3. John Cohen, “Novel Center Seeks to Add Spark to Origins of Life” Sciences 270: 1925–1926 (December 22, 1995).
  4. Adam B Johnson, “The Miller Volcanic Spark Discharge Experiment”, Sciences 322 (October 17, 2008), 404.
  5. Kevin Zanley, Laura Schaefer, and Bruce Fegley, “Early Earth’s Atmosphere,” Cold Spring Harbor’s Perspectives on Biology 2 (10), a004895 (October 2010) (“Geochemical evidence in the oldest igneous rocks on Earth indicates that the redox state of the Earth’s mantle has not changed during the past 3.8 Gyr”); Dante Cannell, “Vanadian in peridot, oxidation and reduction in tectonic environments: Archean to the present,” Earth and Planetary Science Letters 195: 75-90 (2002).
  6. David W. Demer, “First Living Systems: A Bioenergy Perspective,” Microbiology and molecular biology reviews 61: 239 (1997).
  7. The Council for Space Studies of the National Research Council, Searching for the origins of life (Washington, D.C.: National Academy Press, 1990).
  8. Deborah Kelly, “Is it time to get rid of the ‘primal soup’ theory? NPR (February 7, 2010).