Volcanic Gas Helps Link Up the Building Blocks of Life

A gas emitted by volcanoes, carbonyl sulfide (COS), enables amino acid molecules to form peptide bonds.  That’s what long-time origin-of-life researcher Leslie Orgel and colleagues at Scripps Institute have found.  The reaction is especially productive in the presence of metal ions that act as catalysts, and even better in the presence of oxidizing agents.  Moreover, the bonds form at ambient temperatures, and are not hindered by salty seawater, they state in their paper published in Science.¹
    Science news outlets like EurekAlert are claiming this indicates that “volcanic gas may have played a significant role in the origins of life on Earth,” and that the discovery bridges an important “missing link” in studies of “pre-biotic” chemistry (National Geographic News.  Reza Ghadiri, one of the team, does not think life began at volcanoes, of course, but said, “It puts the whole idea of pre-biotic speculation on sure footing.  It’s something that could have happened.”  Amino acids have been produced in previous origin of life experiments (see 05/02/2003 headline), but, critics of chemical evolution have often claimed that peptide bonds between amino acids do not form readily in water (in fact, water hastens their dissolution).
    The team’s experiments began using one amino acid, phenylalanine, in only the left-handed form.  Several intermediates were produced in the reaction with COS, one of which was “reasonably stable” against hydrolysis with a half-life of up to 20 hours.  That intermediate was concentrated with more L-phenylalanine at alkaline pH 9.0 plus or minus 1.4 in anaerobic conditions, and yielded 6-7% dipeptide in 40-60 hours.  The step from the intermediate to the peptide bond is the slowest.  The team found, however, that metal ions (doubly-ionized lead, iron or cadmium) produced “dramatic rate accelerations” up to fourfold.  Even more effective, oxidizing agents (including oxygen, although not expected to be present on the early earth) produced 63% yield of dipeptide in just 5 minutes, 13% tripeptide, and 3% quadrapeptide and traces of longer chains of 5 or 6 amino acid residues.
    The team also succeed getting chains of another amino acid, serine (left-handed only) and mixtures of serine and phenylalanine.  They then generalized the experiment to others, including L-tyrosine, L-leucine, and L-alanine, in the presence of the lead ion catalyst.  “In all reactions,” they reported, “efficient production of mixed dipeptides and tripeptides was observed.”
    How realistic is the presence of COS in early earth scenarios?  Orgel et al. claim that COS is present in 0.09% of volcanic emissions, but “hydrolyzes rapidly on a geological time scale,” so is “unlikely to have accumulated to a high concentration in the atmosphere.”  A “prebiotic soup” or enriched atmosphere of peptides by the tons is not envisioned, therefore, but rather enrichment at “localized regions close to its volcanic sources.”  Because of the relatively short half-life of the intermediate, “it may be unlikely that a substantial proportion of any amino acids present would have been converted” to the necessary intermediates.  The team suggests a “polymerization on the rocks” scenario, “in which peptides long enough to be irreversibly adsorbed near the source of the COS were subject to slow chain elongation,” especially if metal ions or oxidizing agents were also present.
    “The direct elongation of peptide chains using COS as a condensing agent and the condensations catalyzed by Fe²⁺ or Pb²⁺ ions seem plausible as prebiotic reactions,” they claim.  And who knows; maybe COS was the effective ingredient to speed up other prebiotic reactions, too.  “It remains to be determined whether COS could have participated in prebiotic chemistry in other ways—for example, as an intermediate in the reduction of CO2 and as a condensing agent in phosphate chemistry.”

¹Leman, Orgel and Ghadiri, “Carbonyl Sulfide-Mediated Prebiotic Formation of Peptides,” Science, Science, Vol 306, Issue 5694, 283-286, 8 October 2004, [DOI: 10.1126/science.1102722].

There’s the plausibility criterion again (see 12/22/2003 and 01/15/2004 commentaries).  But how plausible is this series of ad-hoc scenarios?  First, the amino acids (however they got there, from meteorites or wherever) need to find themselves near a volcanic source with all the expected heat and commotion going on, to breathe in that 0.09% COS without getting destroyed in the process.  Then they need some handy doubly-ionized lead, iron or cadmium ions, or oxidizing agents, nearby to speed up the slow reaction before the COS or intermediates get hydrolyzed (i.e., split by the very water they are presumably soaking in).  But simultaneously, the other prebiotic molecules need to be shielded from the salts and oxidizing agents that would destroy them.  Then the lucky dipeptides or tripeptides need to find a handy rock to get adsorbed onto before they fall apart in the water, which hopefully was within the right pH range to begin with.  Good luck.
    Does Orgel really believe that under ideal conditions any chains longer than five or six are going to be produced?  Short chains are no more useful to a cell-wannabee than single amino acids.  What happens with a more realistic experiment consisting of a racemic mixture of left- and right-handed amino acids?  Why did they start with a concentrated, highly improbable one-handed set? (see online book).  Speculation on a “sure footing” is still speculation.  “Could have happened” doesn’t cut it in science.  Lots of things could have happened.  I could have won the lottery 100 times in a row, if I had bought the tickets.  Good thing I don’t have that kind of faith.
    The team can be congratulated for doing some interesting lab work in organic chemistry that adds to our understanding of how certain reactions occur under carefully controlled conditions.  To leap from there and think that it has any relevance to a naturalistic origin of life, however, is like thinking “the existence of plastic explains the origin of Legos.”  This new scenario suffers from all the faults of previous attempts to bridge the canyon between nonlife and life (see 10/31/2002 headline and 05/22/2002 commentary).  Every step in the Darwin Party’s hypothetical naturalistic origin-of-life scenarios is exceedingly improbable.  It is illogical to assume they reinforce each other.  Improbabilities do not add up to probabilities; they multiply into even greater improbabilities.  Even if, against all odds, Orgel succeeded in getting hundreds of peptide bonds, it would not explain the origin of the information needed for a polymer to function in any useful way as part of a system containing genetic instructions and molecular machines.
    Get real; read Creation-Evolution Headlines where, unlike the Darwin-worshipping science news outlets, we let you in on the damaging details camouflaged within the original journal articles instead of squawking like a silly parrot, “Volcanoes May Have Sparked Life on Earth” (National Geographic).  If you believe that, we have a fountain of youth to recommend: Mt. St. Helens.  Jump in and inhale all that life-giving carbonyl sulfide.