Unusual nonterrestrial <scp>l</scp>‐proteinogenic amino acid excesses in the Tagish Lake meteorite
Bibliographic record
Abstract
Abstract– The distribution and isotopic and enantiomeric compositions of amino acids found in three distinct fragments of the Tagish Lake C2‐type carbonaceous chondrite were investigated via liquid chromatography with fluorescence detection and time‐of‐flight mass spectrometry and gas chromatography isotope ratio mass spectrometry. Large l‐enantiomeric excesses (lee ∼ 43–59%) of the α‐hydrogen aspartic and glutamic amino acids were measured in Tagish Lake, whereas alanine, another α‐hydrogen protein amino acid, was found to be nearly racemic (d ≈ l) using both techniques. Carbon isotope measurements of d‐ and l‐aspartic acid and d‐ and l‐alanine in Tagish Lake fall well outside of the terrestrial range and indicate that the measured aspartic acid enantioenrichment is indigenous to the meteorite. Alternate explanations for the l‐excesses of aspartic acid such as interference from other compounds present in the sample, analytical biases, or terrestrial amino acid contamination were investigated and rejected. These results can be explained by differences in the solid–solution phase behavior of aspartic acid, which can form conglomerate enantiopure solids during crystallization, and alanine, which can only form racemic crystals. Amplification of a small initial l‐enantiomer excess during aqueous alteration on the meteorite parent body could have led to the large l‐enrichments observed for aspartic acid and other conglomerate amino acids in Tagish Lake. The detection of nonterrestrial l‐proteinogenic amino acid excesses in the Tagish Lake meteorite provides support for the hypothesis that significant enantiomeric enrichments for some amino acids could form by abiotic processes prior to the emergence of life.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".