This article is from
Journal of Creation 37(1):120–128, April 2023

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The origin of L-amino acid enantiomeric excess: part 2—by preferential photosynthesis using circularly polarized light?

by Royal Truman

Several mechanisms have been proposed to explain the origin of homochirality, the use of only one enantiomer in constructing proteins, RNA and DNA.¹ The best-known theory for L-amino acids (L-AAs) involves asymmetric photochemistry of AAs present in space by UV right-circularly polarized light (r-CPL), discussed in part 1 of this series.² CPL is an electromagnetic wave, the electric field vector of which traces a spiral in the direction of propagation, as shown in figure 1.

Rubenstein et al. suggested, in 1983, that regions on opposite sides of the plane of predominant polarization would be exposed to light of opposite helicity, although overall symmetry would be preserved.³ Key papers followed up on this suggestion.^4-7 Enantioenriched photoproducts were proposed to have been delivered to Earth by comets and meteorites.^8,9

Approximately 1% enantiomeric excess (ee) has been claimed for some AAs in optimized synchrotron experiments after photo-destroying 99.99% to 99.999% of racemic D- and L-AA mixtures. A specific wavelength was selected to optimize the miniscule effect.¹⁰ However, different wavelengths selectively destroy D- or L-AAs, tending to annul any net effect.² In addition, a specific AA, leucine (Leu), was emphasized in these experiments, known to have an abnormally large difference in molecular absorption coefficient (ε) when using UV CPL.²

Experiments producing racemic amino acids

Earth’s early atmosphere was supposedly non-reducing, with CO₂ being the main source of carbon.¹¹ But experiments using high energy sources (acting on gas mixtures thought to reflect the putative ancient Earth atmosphere) to generate reactive fragments have produced, at most, trace amounts of only the simplest AAs.¹¹ Therefore, a more suitable chemical environment had to be found.

Muñoz and colleagues performed some experiments in 2002, showing that AAs form at very low temperatures using UV light.¹² An ice mixture containing H₂O, CH₃OH, NH₃, CO, and CO₂ in 2:1:1:1:1 molar proportion was placed in a high-vacuum chamber at 12 K and irradiated with UV light having energy 7.3–10.5 eV, mostly around 10.2 eV, which corresponds to a wavelength of λ = 121.6 nm.¹² After warming to room temperature, the small amount of residue formed was hydrolyzed with 6 N HCL to extract AAs from larger materials such as peptides. 16 AAs were identified, 6 of which are found in proteins. Glycine was by far the major product. It is important to recall, though, that glycine and other AAs have so far not been detected in the interstellar medium.¹²

Similar results were obtained when the carbon-containing molecules were isotopically labelled (i.e. using H₂O, ¹³CH₃OH, NH₃, ¹³CO, and ¹³CO₂) to determine from the products if terrestrial contamination was occurring. No evidence for contamination was found but now valine and proline were not detected.¹² This illustrates the technical difficulties of these kinds of experiments and the caution needed when reading the papers.

In studies like these and those which report the proportion of D- and L-AA enantiomers from meteorites statistical analysis reveals something remarkable. In a significant majority of cases when the enantiomeric proportions are within experimental error, more L is reported. The difference is often less than 1% and believed to be within random experimental error, but why is the error not randomly distributed? This appears to be an example of bias in data cleanup and selection of which repeated measurements were included in averages and how the results were described.¹³ Concerning the principle of researcher bias, we read in this study that

“As expected for photosynthesis using unpolarized light, the amino acids produced appeared to be racemic, with enantiomeric excesses fluctuating within experimental errors [emphases added].”¹²

And what should be considered experimental error? The L/D ratio for serine reported was 3.86 / 3.29 depending on the helicity of the CPL. This corresponds to an enantiomeric excess of 100 × (3.86 – 3.29) / (3.86 + 3.29) ≈ 8%. For aspartic acid, the only case in which the D enantiomer predominated, L/D was 1.07 / 1.14, which corresponds to ee_L = –3.2%. Empirical calibration errors could creep into these kinds of studies, since the AAs are usually chemically derivatized to facilitate GC (gas chromatography) or LC (liquid chromatography) analysis, and the resulting labelled diastereomers have different relative spectral absorptivity. In the majority of cases, corrections are necessary, creating opportunities for errors.¹⁴

When there is a consensus that a racemic mixture must result, then even 8% ee_L was not further commented on, but the opposite also occurs routinely. To illustrate, the first studies on the Murchison Meteorite reported that the biogenic AAs were racemic and this was used as evidence for lack of terrestrial contamination.^15-17 These researchers had selected the best fragments available and presumably believed L-AAs could have arisen on earth for origin-of-life purposes. Later, other evolutionists wished to show that AAs having an excess of L-form may have been the source of original homochirality and reported their results from experiments based on less pristine samples, when contamination was more likely to have accumulated. They now claimed small excesses were found, far under 8% ee, results the original researchers strongly claimed were experiment artefacts.¹⁸ Scientists must be very wary about claims which are very close to being within experimental error where not all the repeated tests are reported and the experiments are technically difficult to reproduce, whereby the results support a favoured but controversial view. Confirmation bias can occur unconsciously or deliberately.

It is assumed that tiny silicate and carbon-based interstellar dust grains may have provided an environment to form very simple molecules which served as building blocks for biologically relevant more complex molecules. Accretion from the gas-phase collisions, and chemical reactions on the surface would coat the grain with refractory carbonaceous matter. These grains would eventually contain frozen H₂O, CO₂, CO, NH₃, as well as small amounts of CH₃OH, CH₄, H₂O, and HCOOH.¹⁹

In another experiment, also published in 2002, Bernstein et al. created ice films at 15 K consisting primarily of H₂O mixed with 0.5–5% NH₃, 5–10% CH₃OH, and 0.5–5% HCN, relative to H₂O.¹⁴ UV irradiation used light nearly evenly divided between the Lyman α-line (121.6 nm) and a ~20 nm wide source centered at 160 nm. Each sample was photolyzed with a photon flux corresponding to ~500 years at the edge of a dense cloud.¹⁴ After deposition and photolysis, the ices were warmed at ~2 K/min under dynamic vacuum at ~10^–8 torr to room temperature, leaving behind an organic residue, which was hydrolyzed with concentrated HCl to produce free AAs. ¹⁴ Three AAs were identified, serine, glycine, and alanine. The chiral ones (serine and alanine) were found to be racemic within the integration error (100.1 ± 1.6%) using GC-MS.

Experiments producing an enantiomeric excess

Meierhenrich reported in 2010 that enantiomers in aqueous solution could absorb slightly differently at a given wavelength.²⁰ To obtain a small L-excess, a researcher must carefully expose a racemic mixture of an AA to CP UV light of the ‘correct’ wavelength(s). Of course, the same L-AA will absorb less strongly than its D-AA counterpart at another wavelength, counteracting the desired outcome.

The first cosmic ice simulation experiments that produced an AA (alanine) with enantiomeric excess was reported in 2011 by a team led by Nahon and d’Hendecourt.²¹ They used a gas mixture of H₂O:¹³CH₃OH:NH₃ (2:1:1) at 80 K irradiated with an energy of 6.64 eV (186.7 nm) for ~36 hr in a high vacuum chamber. The high temperature (80 K) was used instead of the observed temperatures for interstellar ices (10–20 K) to enhance formation of photoproducts within the ices. After warming to room temperature at a rate of 1 K /min the samples were irradiated at room temperature for another 10 hrs. The samples were then hydrolyzed with 6 M HCl at 110°C for 24 hrs to extract free AAs.²¹

This led to an ee_L of –1.34% (±0.40%, 3σ) alanine using r-CPL vs. +0.71% (±0.30%, 3σ) when using l-CPL. An approximately twice as intense UV beam was used in the case of r-CPL, which might explain the difference in ee (i.e. more photolysis would have occurred). No isovaline (which has the highest ee reported from meteorite carbonaceous chondrites) was identified. The major product was glycine, 14 times more abundant than the second most abundant AA, alanine. ²¹

Nahon and colleagues from the SOLEIL Synchrotron in France reported other experiments in 2013. They monitored the spectra of gaseous neutral alanine molecules photoionized with CPL having a fixed photon energy of hv = 10.2 eV (121.6 nm). This energy can only eject photoelectrons from the highest occupied molecular orbital of neutral alanine.^21,22 From the spectral data, the researchers estimated that at interstellar temperatures ranging from 10 to 200 K about 0.5 – 2% of the alanine molecules would survive ionization at 10.2 eV. If some alanine had survived this irradiation, they thought that a maximum of 4% ee could have been attained in the limit of pure CPL, based on a mathematical model.²¹ Their conceptual scenario assumed that a racemic mixture of gas-phase alanine would be embedded into a CPL field with a given and constant helicity over a large region of space.

Clearly these kinds of studies are artefacts from carefully designed laboratory experiments. The concentration of racemic alanine would have been infinitesimally low, of which almost all would have to be destroyed through irradiation to produce a very small ee, using just the right CPL wavelength and unmixed helicity. To put things in perspective, so far, the only AA claimed to have been detected in the interstellar medium is glycine, which is not even chiral. Even this observation remains unlikely since some spectroscopic lines which should have been present were not found.²³

The only evidence from astronomy for circular polarization involves near-infrared wavelengths, thought to arise from the scattering of stellar radiation from aligned dust grains. ^2,24 This part of the electromagnetic spectrum has no relevance to AA photo-destruction, because the photon energy is too low. Destruction can be caused by higher energy UV (<300 nm) absorbed by the carboxylate chromophore attached to the α-carbon.

As already emphasized, despite intense effort, no astronomical UV CPL has been found. In part 1 of this series, it was shown that the small enantiomeric excess increases and reverses depended on the UV wavelength, and there is no reason why only r-CPL would have existed.² The hypothetical scenario would have produced <1% ee_L after photo-destroying over 99.999% of the racemic AA. Slow, extraterrestrial influxes of this concentration and purity render naturalist origin-of-life models even less plausible, especially since the miniscule ees would have racemized on Earth in water during long geological times.

Irradiation of CO, NH₃, and H₂O at very high energy

In another study a gaseous concentrated mixture of carbon monoxide, ammonia, and water was irradiated with high-energy 3.0 MeV protons from a van de Graaff accelerator.²⁵ A complex mixture of organic materials was obtained having molecular weight ranging from several hundred up to 3,000 Daltons. This mixture was then irradiated with UV r-CPL and l-CPL having wavelengths >200 nm.

After UV–CPL irradiation, the material was hydrolyzed with 6 M HCl at 110°C for 24 h to extract free AAs. Seven biogenic AAs were identified, where glycine predominated. No leucine was found. The r–CPL is claimed to have produced alanine having ee_D = 0.44% and using l-CPL to an ee_L = 0.65%.²⁵

These results are consistent with other simulation experiments using proton irradiation, UV irradiation and gamma-ray irradiation under simulated interstellar environments. These conditions, however, were not shown to form free AA precursors which might lead to AAs.²⁵ These studies also showed that the chemically bound AA analogs formed were photochemically much more resistant to destruction by gamma rays and UV irradiation than free AA analogs.²⁵

Photosynthetic mechanisms?

Producing an enantiomeric excess of L-AA is almost always assumed to require selective photo-destruction of 99.99% or more of the AA using CPL. Perhaps more efficient mechanisms exist to directly synthesize AAs aided by CPL. However, as Meierhenrich et al. pointed out in a 2018 review article, “Investigations on the absolute asymmetric synthesis of amino acids are scarce.”²⁶

Photosynthesis of AA using unpolarized UV light

To find potential paths able to produce an extraterrestrial enantiomer excess, it is helpful to identify photochemical mechanisms which produce AAs. In 2016 Oba et al. examined a mixture of CH₂DOH, H₂O, CO, and NH₃ in a ratio of 2:5:2:2, irradiated at 115–170 nm for 20 hrs at 10 K.²⁷ The use of deuterated methanol (CH₂DOH) helped establish what radical species are involved in forming which products.²⁷ At this wavelength photodissociation of methanol is known to form specific radicals, as shown in figure 2A.^28,29 In addition, unimolecular hydrogen molecule elimination (UHME) will also occur, as shown in figure 2B.^28,30

Glycine, α-alanine, β-alanine, sarcosine, and serine, and various isotopologues having a deuterium (D) atom bound to carbon atoms, were found in organic residues formed after warming up to room temperature. For simplicity, the deuterated products are not shown in figure 2. The abundances of AAs obtained increased by a factor of more than five after hydrolyzing the organic residues.

The researchers assumed that these five AAs were produced by reactions of small radicals during warming of the irradiated ice and that most AAs formed were incorporated into macromolecules via relatively weak bonds such as peptide bonds.²⁷

The kinds of radicals formed and their proportion will depend on the compounds available. It seems highly unlikely that CPL of a single handedness would produce radicals which lead to predominantly D- or L-AAs. This is especially true when considering that slow warming in space over thousands of years to permit radicals to combine into stable bonds would tend to produce racemic products. Nevertheless, experiments have been conducted to determine if an ee could be obtained.

Photosynthesis of AA using CPL UV light

Pioneering work to determine whether an ee_L could be produced through photochemical synthesis (instead of selective photochemical destruction) was reported by Nuevo et al. in 2006.^31,32 The authors prepared interstellar ice analogs by depositing equimolar H₂O, ¹³CH₃OH and NH₃ onto a cooled substrate at 80 K and irradiating either with r- or l-CPL at 167 nm, see figure 3. The authors reported an ee <1% for α-Ala and 2,3-diaminopropanoic acid.

In a key 2014 study conducted at the SOLEIL synchrotron facility in France, Modica et al. irradiated water, methanol, and ammonia ice in a ratio of ~2:1:1 H₂O, ¹³CH₃OH and NH₃ with an intense UV beam.³³ Methanol was labelled with ¹³C to help distinguish between true products and terrestrial contamination during the experiments.³³

The experiments were carried out at 77 K in a high-vacuum chamber at a pressure <10^–7 mbar, linked to a Fourier transform infrared spectrometer. Separate experiments used different UV wavelengths, 188 nm (6.6 eV) and 122 nm (10.2 eV). In some experiments, the original ices were irradiated, in others, organic residues resulted. In the third type of experiment, both ice and organic residues were irradiated.³³

At the end of the irradiation, the ice samples were slowly warmed at 1 K/min to room temperature (to allow diffusion of free radicals and subsequent recombination). During this process, the volatiles (~99.9% of the products formed), sublimated and were removed by the pumping system. Solid residue was obtained at room temperature. Hydrolysis was performed on the residue material using 6 M HCl for 24 hr at 110°C to liberate free AAs which were analyzed with multidimensional GC.³³

The researchers identified 16 distinct AAs (24 counting individual enantiomers), see table 1.

The measured ee_L values for alanine as a function of the photon energy (i.e. wavelength), the stage at which the samples were irradiated by CPL, and the helicity of CPL used are shown in table 2. The experiments were conducted at different times and under differing experimental conditions, such as photon flux per deposited molecules and concentrations of the extracted samples; therefore, comparing the absolute ee values is difficult.

Remarkably, the results from irradiation of the ice might indicate that the reactions of the radicals are affected by the helicity of the CPL. This would imply that the ee_L of alanine is not only caused by selective photolysis. In any event, the possible excess would be very small. Recall that in experiments above using unpolarized light, ee values of 3% and 8% were stated to be racemic within experimental error.

Of the products formed, the enantiomeric excess of five were measured: α-alanine, 2,3-diaminopropionic acid, 2-aminobutyric acid, valine, and norvaline, with ee_L values ranging from –0.20% ± 0.14% to –2.06% ± 0.34%, as shown in table 3. The statistical uncertainties reported were based on multiple gas chromatographic injections for each sample (up to 10), and not repetition of the entire experimental protocol.³³ We are not informed why the number of repetitions ranged from 3 to 7, since repeating GC runs is very easy.

As discussed in part 1,^2,9 due to the wavelength dependence of asymmetric photochemical reactions, the sign of the induced ee_L depended, for the five AAs examined, on the helicity and the energy of CPL.

It is noteworthy that the ee_Ls were induced in both the ice-only and residue-only samples irradiated by CPL. In the case of the irradiation of the water/methanol/ammonia ices, a two-step reaction may be occurring:

• Step 1. Initially the CPL forms ions, radicals, and/or small molecules which possess a chiral centre (these could also be induced by ordinary unpolarized light).
• Step 2. Asymmetric photochemical processes then occur on the chiral intermediates, preferentially producing one of the enantiomers. For example, a precursor enantiomer could be selectively asymmetrically photolyzed.³³ The recombination reactions which occur during the warming up phase of the ices without any further irradiation appear to retain an impact of the effect caused by the chiral CPL field.³³

In the case of irradiation of the residue using CPL of only one helicity, racemic mixtures of chiral molecules were present. Presumably destructive photolysis of one enantiomer occurred, as described in part 1.^2,33 That mechanism requires photoreduction of >99.99% of racemic AAs to produce an enantiomeric excess of about 1% of one of the enantiomers.

The five AAs in table 3, when irradiated with r-CPL, always led to an excess of L-enantiomer, and l-CPL to an excess of the opposite enantiomer. Notably, the unpolarized light should have always produced racemic mixtures but did not. In fact, the average of six or seven measurement repetitions produced ee_L values ranging from –0.05% to +0.67%, as shown in the right-most column of table 3. In two of the five AAs, irradiation with UPL led to absolute ee_L values of over 0.6%.

Unexpectedly, for α-alanine a larger absolute ee was reported when irradiated with UPL than l-CPL (0.46 vs –0.34). The same unexpected behaviour was also obtained for 2,3-diaminopropionic acid (0.67 vs –0.20). Therefore, ee_L results between ±%1 might be spurious, representing about half of the results when applying r-CPL and l-CPL in table 3. This suggests that identifying real ee’s, even under ideal experimental conditions, is quite difficult.

Furthermore, the authors pointed out that the presence of ¹²C fragments in the mass spectra demonstrated terrestrial contamination especially in the case of alanine.³³ This is the second most abundant AA found in human proteins, after leucine, raising the possibility of accidental contamination during experimental handling. This contamination occurred despite great care to prevent it. This illustrates how easy it is to also pick up terrestrial contamination of L-AAs when studying the composition of meteorites, in which sometimes ee_L values of ~1% have been claimed.

Astronomical significance

The best candidates for CPL sources have been proposed to be reflection nebulae in star-forming regions associated with a dominant high-mass young stellar object.³³ High levels of CPL have been observed in the near-IR (NIR) spectra in reflection nebulae such as OMC-1, at levels of −5 to +17%^5,34-36 and more recently in NGC 6334, at levels of 22%.^37,38 To date, however, no chiral molecule has been identified in the interstellar medium.³³

Modica et al. proposed an astrophysical scenario in which the solar system was formed in a high-mass star-forming region where icy grains in the outer solar nebula might have been exposed to irradiation of a single helicity, inducing a stereo-specific photochemistry.³³ The grains on which molecules were photosynthesized could have accreted on comets and asteroids. At that point the molecules may have been shielded from further UV exposure until their delivery to the early Earth during or just after the late heavy bombardment.³³

Chondrites are stony meteorites which contain small mineral granules called chondrules. Carbonaceous chondrites comprise about 3% of all meteorites collected and are of interest because they contain a high proportion of carbon (up to 3%). They are subdivided into six groups based on their chemistry and other criteria (CI, CM, CV, CO, CR, and CK). If photosynthetic routes had formed large ee_Ls for AAs in putative presolar ices, this would be apparent across the various meteorite classes. However, the relative proportions of D- and L-enantiomer for α-AAs do not support this. The non-proteogenic isovaline (which lacks an α-hydrogen and is therefore very difficult to racemize) is an exception with more L-isovaline enantiomer being reported for the small minority of meteorites of class CR. This excess was not even found in meteorite classes CR2 and CR3, though.³⁹

An important observation is that the relative absorptions of UV CD spectra of the α-methylated AAs L-isovaline and L-α-methyl valine are in the opposite direction to those of protein relevant enantiomers of α-H AAs.⁴³ Therefore, their putative presence would predict an excess of the ‘wrong’ D-α-hydrogen AAs being delivered to Earth.⁴⁰

Conclusions for origin-of-life purposes

In experiments like those discussed above, high energy sources were used to produce charged chemical fragments or radicals, which then combined to produce various molecules, including trace quantities of AAs. High energy sources such as UV light, protons, intense shock, or electric discharge as used in the Miller-Urey experiments can of course do this.⁴¹ In some experiments, the energy source was CPL and in others, r-CPL or l-CPL was applied after the fragments or molecules had formed.

Most authors claim that their experimental conditions reflect some degree of plausibility to natural conditions. We see instead that in all cases an intended outcome determined how the experiments were expertly set up. To produce AAs, reactive carbon-, nitrogen-, and hydrogen-containing fragments were produced in very high concentrations, thanks to the near ideal relative stoichiometries at the same location; high concentration of starting materials; intense energy source; and use of a closed container. Forming key -CO, -NH and -CH fragments was inevitable under the expertly guided conditions, and the intended chemical reactions were inevitable upon careful warming up since the reactive fragments formed were not allowed to simply diffuse into free space. Typical heating rates of icy mantles under astrophysical conditions are on the order of only 1 K per century. This influences the mobility of reactants as they desorb in the ices.¹⁹ However, laboratory studies on the photostability of AAs have demonstrated their limited survival when exposed to interstellar UV irradiation over a wide range of wavelengths near 200 nm and cosmic rays.^42-45 Only a small proportion might be embedded in chemically bound form in the interior of comets and asteroids and thus shielded from the destructive radiation.¹⁹

The importance of producing large numbers of concentrated reactive fragments by experimental design is demonstrated by the considerably greater variety of products generated upon producing greater amounts of residue.³³

Obtaining an enantiomeric excess then required further expert guidance. Whether a positive or negative ee_L resulted depended on the wavelength of irradiating CPL. In outer space this effect would cancel out almost entirely since natural sources of CPL would be spectrally broadband.³³ Recalling that an excess of r-CPL or l-CPL has never been found by astronomers, we see, in addition, that the experiments used only one or the other, and at a wavelength already known to be absorbed more strongly by one AA enantiomer.

One might argue that, by chance, the UV wavelength distribution might have been such that photolysis destroyed more of the D-enantiomer. For example, aliphatic AAs have a strong absorption UV band centred at about 210 nm. However, as Belgian scientists Cerf and Jorissen noted, other biogenic AAs having additional functional groups show the opposite effect in the same region.⁶ An example is tryptophan, which has a strong circular dichroism (CD) band centred at about 195 nm, with an opposite sign to the carboxyl 210 nm band. Proline is another example, with a strong CD band of opposite sign around 193 nm in a neutral solution.⁶ Therefore, an ee_L for all the relevant AAs would not have been produced.

CD spectra for l-CPL and r-CPL are needed to determine how severe this problem is, and these must be measured for neutral AAs and not in aqueous solutions, to reflect conditions in space. Other AAs exhibit complex CD absorption due to the presence of other chromophores in their side chain such as an aromatic ring for phenylalanine, tyrosine, and tryptophan and a sulfur-containing group for cysteine and methionine.⁶

Having set up experiments which do not reflect any known natural astronomical conditions, the researchers were able to obtain, at best, an ee_L ~1%, present in vanishingly small concentrations. Recall that about 99.99% photo-destruction was necessary, but of course 100% must not occur!

Although no UV CPL from astronomical sources has ever been found, Bailey et al. gave some thought about how high an ee_L could be if more L-AAs were produced under optimal conditions. They pointed out that the global ee on an ancient post-bombardment Earth would be less than that of the original source material due to racemization (with full racemization estimated at 10⁶ years at 0°C to 10³ years at 50°C).⁴⁶ They also noted correctly that dilution with terrestrially produced racemic AAs would also have reduced the excess. They then proposed that the global ee would be in the range of 5 × 10^–3 to 10^–7. The higher value assumes 50% of the AAs were of extraterrestrial origin, having 10% ee and a racemization time scale of 10⁶ years. The lower estimate is based on a 1% extraterrestrial source of AAs having 10% ee and a 10³-year racemization timescale on average for each kind of AA.⁴⁶ This is not plausible. An estimate of ee_L ≈ 10^–7 for biogenic AAs (even though already fatal for the claimed basis of AA ee) would still be far too high. Let us see why.

Sometime after a putative late heavy bombardment, AAs would have become thermally stable as the earth cooled. For a few million years the oceans would have remained extremely hot and accumulated perfectly racemized AAs. In fact, complete racemization at around the boiling temperature of water would have occurred in a matter of only days.³ Evolutionists believe AAs were delivered slowly via cometary and asteroid impacts or perhaps when the earth traversed molecular clouds.^6,33 Most of the AAs would have been in chemically bound state, but under the still very high temperature conditions hydrolyzed to form free AA, which then racemized.

After eventually cooling to about 50°C (where the authors assumed a racemization time of 10³ years) it is inconceivable that extraterrestrial AA now arriving would constitute 1% of the total amount present (since c. 100% racemized AA would have accumulated from all sources over millions of years). The freshly arriving AAs would need to survive the heat generated during passage through the atmosphere and the impact with the earth. Most of the new AAs arriving would be chemically bound, and not land in an environment of 6 N HCl at over 100°C (the conditions to free the AAs in a laboratory). Any conditions able to free these bound AAs faster, such as higher temperatures or basic catalysts, would have also accelerated the rate of racemization.⁴⁷

Furthermore, photochemical reactions producing AAs in the presence of UV CPL would be far less frequent than in the presence of unpolarized UV light, the only kind of UV radiation found in space to date. Therefore, an extraterrestrial influx having 10% ee on average from all sources for all biogenic AAs is not realistic. One does not observe all AAs displaying such high ees across all meteorite classes, not even for leucine, the exceptional case which might be able to produce an ee. Most of the AAs of extraterrestrial origin show no ee, and the exceptions are on the order of 1–2% ee, widely assumed to be caused by terrestrial contamination.

Note that as time passed, the total volume of racemized AA on an early earth would have steadily increased, leading to ever greater dilution of newly arriving AAs having a putative ee_L. Under plausible evolutionary prebiotic scenarios an ee_L <<10^–7 would have to be assumed for all time periods.

Water is necessary to dissolve AAs and peptides, and indeed most of the AAs arriving would have landed in water or been flushed into an ocean over time. However, peptide elongation in water is always slower than racemization, so production of large homochiral peptides would not have occurred.⁴⁸ As the German evolutionist chemist Dr Günter Wächtershäuser pointed out (translated):

“The primordial soup theory has faced devastating criticism for being illogical, inconsistent with thermodynamics, chemically and geochemically implausible, inconsistent with biology and biochemistry, and experimentally disproved.”⁴⁹

This source of ee_L, based on hypothetical and idealized reaction conditions, makes no useful contribution to a naturalist explanation for the origin of homochiral biopolymers. In fact, it appears to be terminally damaging to the speculations that are still popularized, without substantiation, in the literature. Evolutionists are left to make do as best possible, however, and further speculate that miniscule excesses of L-enantiomers once present may have separated from the D-enantiomers (the L-AAs were ‘amplified’). These proposals will be critiqued in future papers, noting also that physically separated L-AAs in isolated crystals are unsuitable for any origin-of-life scenario. They need to redissolve, where remixing simply soon regenerates the racemic mixture.

The theoretical availability of biogenic AAs having ee_L <<10^–7 would be utterly inadequate to produce peptides with any kind of secondary structure, a minimum requirement to form stable folded proteins. Forming the smallest biologically relevant secondary protein features requires on average about 95% pure L-AAs.⁵⁰