Squeezing the Last Life Out of the Miller Experiment
Can the dead live again? The Miller-Urey experiment of 1953, with its iconic spark-discharge flasks producing amino acids in a simulation of the early Earth, was pretty much dead by the turn of the millennium. Jonathan Wells wrote:
The Miller-Urey experiment is still featured prominently in textbooks, magazines, and television documentaries as an icon of evolution. Yet for more than a decade most geochemists have been convinced that the experiment failed to simulate conditions on the Earth, and thus has little or nothing to do with the origin of life. (Icons of Evolution, p. 10)
Now, rummaging through Stanley Miller's vials, some of Miller's followers say they've found enough unpublished evidence to resurrect the icon.
NASA's Astrobiology Magazine was among 65,000 sites that echoed the report of "Stanley Miller's Forgotten Experiments" around the Internet. Miller's second graduate student, Jeffrey Bada, had inherited those vials after his mentor suffered a stroke in 1999. In some vials from 1958, more amino acids were found than those in the original 1953 experiment. The difference was caused by the addition of a new ingredient, cyanamide, to the flask. Bada and Eric Parker (that's him the video above) of the University of Georgia have published the results of their replications of those experiments from 1958 in Angewandt Chemie, "A Plausible Simultaneous Synthesis of Amino Acids and Simple Peptides on the Primordial Earth." The abstract explains why this ingredient enhanced the output:
Following his seminal work in 1953, Stanley Miller conducted an experiment in 1958 to study the polymerization of amino acids under simulated early Earth conditions. In the experiment, Miller sparked a gas mixture of CH4, NH3, and H2O, while intermittently adding the plausible prebiotic condensing reagent cyanamide. For unknown reasons, an analysis of the samples was not reported. We analyzed the archived samples for amino acids, dipeptides, and diketopiperazines by liquid chromatography, ion mobility spectrometry, and mass spectrometry. A dozen amino acids, 10 glycine-containing dipeptides, and 3 glycine-containing diketopiperazines were detected. Miller's experiment was repeated and similar polymerization products were observed. Aqueous heating experiments indicate that Strecker synthesis intermediates play a key role in facilitating polymerization. These results highlight the potential importance of condensing reagents in generating diversity within the prebiotic chemical inventory. (Emphasis added.)
We see right off the bat that Miller's purpose in 1958 was to study the polymerization of amino acids. He didn't really produce any new amino acids, except when he added hydrogen sulfide (H2S) to the flasks that same year (strangely, he never published those results either, so Parker and Bada repeated the experiment in 2011). Alongside a historic photo of Stanley Miller proudly standing by his spark-discharge apparatus, NASA says:
The latest study is part of an ongoing analysis of Stanley Miller's old experiments. In 2008, the research team found samples from 1953 that showed a much more efficient synthesis than Stanley published in Science in 1953. In 2011, the researchers analyzed a 1958 experiment that used hydrogen sulfide as a gas in the electric discharge experiment. The reactions produced a more diverse array of amino acids that had been synthesized in Miller's famous 1953 study. Eric Parker was the lead author on the 2011 study.
Strecker synthesis was intelligently designed by Adolph Strecker in 1850 to generate amino acids through a series of reactions with artificially supplied reagents. Its contribution to this discussion, therefore, is nil, because no chemists were present at the origin of life. Bada and Parker need to account for naturally occurring "condensing reagents" in early-Earth conditions.
The diketopiperazines can be dismissed, too, because they are either found in life or synthesized by intelligent design (see paper in Chemistry and Biology, 2010).
What we should focus on is the addition of cyanamide and hydrogen sulfide to Miller's 1958 experiments. Is this something to get excited about?
Cyanamide (NCNH2) has been detected in interstellar space. Bada and Parker can therefore call it "the plausible prebiotic condensing reagent cyanamide" by presumably ferrying it to Earth in meteorites. (Just how plausible this may be is debatable.) In the lab, the Frank-Caro process requires temperatures of 1,000° C to produce cyanamide. Once you have it, you can use it as a dehydration agent to generate other organic molecules. Bada and Parker give it a role in the peptide condensation reaction, but their abstract only mentions dipeptides (two amino acids joined together). Proteins and enzymes are typically hundreds of amino acids long.
Hydrogen sulfide (H2S) is sometimes detected in volcanic gasses, although it is usually produced by biological sources. Bada and Parker can therefore expect this molecule to provide some of the reducing conditions for the origin of life.
That's about the only good news astrobiologists can expect, though, because all the old criticisms of the Miller experiment by Jonathan Wells still apply:
(1) They still used the wrong gasses: methane, ammonia, and water vapor. For decades, geochemists have not considered it likely these gasses were abundant in the early Earth atmosphere.
(2) They still ignored the presence of oxygen, which destroys the desired products. Wells explained that oxygen was likely abundant due to photodissociation of water in the atmosphere. The oxygen would remain, while the hydrogen would quickly escape to space.
(3) Even if trace amounts of ammonia or methane and other reducing gasses were present, they would have been rapidly destroyed by ultraviolet radiation.
(4) No amino acids have been generated in spark-discharge experiments using a realistic atmosphere of nitrogen, carbon dioxide and water vapor, even in the absence of oxygen.
To this we could add more problems:
(5) The amino acids produced were racemic (mixtures of left- and right-handed forms). Except in rare exceptions, life uses only the left-handed form. Astrobiologists need to explain how the first replicator isolated one hand out of the mixture, or obtained function from mixed-form amino acids initially, then converted to single-handed forms later. Neither is plausible for unguided natural processes -- especially when natural selection would be unavailable until accurate replication was achieved.
(6) Undesirable cross-reactions with other products would generate tar, destroying the amino acids. Only by isolating the desired products (a form of investigator interference -- one might call it intelligent design) could they claim partial success.
(7) Amino acids tend to fall apart in water, not join. Under the best conditions with cyanamide, Bada and Parker only got dipeptides. Repeated cycles of wetting and drying would need to be imagined for polymerization, but many astrobiologists today think life originated at deep sea hydrothermal vents.
(8) The desired reagents would be extremely dilute in the oceans without plausible concentrating mechanisms. Even then, they would disperse without plausible vessels, like cell membranes, to keep them in proximity.
(9) Lifeless polypeptides would go nowhere without a genetic code to direct them.
(10) The Miller experiments cannot speak to the origin of other complex molecules needed by life: nucleic acids, sugars, and lipids. Some of these require vastly different conditions than pictured for amino acid synthesis: e.g., a desert environment with boron for the synthesis of ribose (essential for RNA).
NASA's celebration of the iconic Miller experiments as "a piece of scientific history" is, therefore, much ado about nothing. But since it is such a valuable icon to Darwinists, there will be a lot of ado:
The study discovered a path from simple to complex compounds amid Earth's prebiotic soup. More than 4 billion years ago, amino acids could have been attached together, forming peptides. These peptides ultimately may have led to the proteins and enzymes necessary for life's biochemistry, as we know it.
It may be a beautiful theory to some, but as Thomas Huxley pointed out, many a beautiful theory was killed by an ugly fact. We just gave you ten ugly facts that kill the Miller icon. It's not going to live again.