Evaluating the biosignature potential of ammonium in Proterozoic red beds and implications for the search for life on Mars
Bibliographic record
Abstract
Over the past two decades, it has become increasingly apparent that early Mars may once have been warmer, wetter and more habitable for microbial life than it is today, which has spurred discussions about potential biosignatures that may be preserved in Martian sediments. An impediment to this line of research is the pervasive oxidation of Mars’ surface due to photochemical oxidants that have likely destroyed remnants of organic matter. Here, we investigate whether nitrogen (N) transferred from biomass to phyllosilicate minerals during diagenesis can be preserved in oxidized mudrocks. We investigate two sequences of terrestrial Proterozoic red beds, namely the Sibley Group (1.4 Ga) in Canada and the Stoer Group (1.2 Ga) in Scotland, and we find enrichments in authigenic N in the range of several tens of ppm in both units. The highest concentrations (ca. 100 ppm on average) are found in the most desiccated red beds of the Stoer Group, concurrent with enrichments in potassium (K). We discuss similarities and differences between the two sets of rocks with regards to salinity, pH, biological productivity and K-metasomatism, and we conclude that the ideal mechanism for the preservation of biogenic N in red beds may be in-situ release of ammonium from microbial mats into the clay substrate, possibly facilitated by early diagenetic, biologically induced illitization. Illite and smectite have been observed on Mars, and experiments suggest that Martian waters contained moderate amounts of dissolved K. Hence, it is conceivable that a similar K and N enrichment process could have occurred as to what we document for the Proterozoic, preserving evidence of life that may have survived to the modern day.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".