An Experimental and Theoretical Investigation of HCN Production in the Hadean Earth Atmosphere
Bibliographic record
Abstract
A critical early stage for the origin of life on Earth may have involved the production of hydrogen cyanide (HCN) in a reducing, predominantly H 2 atmosphere. HCN is crucial for the origin of life as it is a possible precursor to several biomolecules that make up RNA and proteins including nucleobases, nucleotides, amino acids, and ribose. In this work, we perform an in-depth experimental and theoretical investigation of HCN production in reducing atmospheric conditions (89–95% H 2 ) possibly representing the earliest stages of the Hadean eon, ∼4.5–4.3 billion years ago. We make use of cold plasma discharges─a laboratory analog to shortwave UV radiation─to simulate HCN production in the upper layers of the atmosphere for CH 4 abundances ranging from 0.1 to 6.5%. We then combine experimental mass spectrum measurements with our theoretical plasma models to estimate the HCN concentrations produced in our experiments. We find that upper atmospheric HCN production scales linearly with CH 4 abundance with the relation [HCN] = 0.13 ± 0.01[CH 4 ]. Concentrations of HCN near the surface of the Hadean Earth are expected to be about 2–3 orders of magnitude lower. The addition of 1% water to our experiments results in a ∼50% reduction in HCN production. We find that four reactions are primarily responsible for HCN production in our experiments: (i) 4 N + CH 3 → H 2 CN + H → HCN + H 2, (ii) 4 N + CH → CN + H followed by CN + CH 4 → HCN + CH 3, (iii) C 2 H 4 + 4 N → HCN + CH 3, and (iv) 4 N + 3 CH 2 → HCN + H. The most prebiotically favorable Hadean atmosphere would have been very rich in CH 4 (>5%), and as a result of greenhouse effects, the surface would be likely very hot. In such a prebiotic scenario, it may have been important to incorporate HCN into organic hazes that could later release biomolecules and precursors into the first ponds.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".