An early origin of oxygenic photosynthesis delays the Great Oxidation
Bibliographic record
Abstract
The Great Oxidation Event (GOE) was the most significant chemical revolution in Earth's history, occurring 2.4 billion years ago. The metabolism that made this transition possible, oxygenic photosynthesis, may have evolved as early as the Eoarchean (3.5 Ga) and certainly by the end-Archean. A long period with low oxygen was facilitated by rapid atmospheric oxidation reactions prior to ozone layer formation, but the mechanisms controlling the length of the delay remain unknown. In this paper, we use EONS (Earth Oxygenation and Natural Systematics), a new biogeochemical model of the Earth system, to evaluate different scenarios for the evolution of two key metabolic pathways-oxygenic photosynthesis and nitrogen fixation, and inorganic phosphorus cycle boundary conditions to constrain determinants of oxygenation timing. We find, counter-intuitively, that an early origin of oxygenic photosynthesis leads to a longer delay before the GOE, and that the earliest-modelled origins delay the Great Oxidation the longest in absolute terms. The ultimate control over oxygenation delay is phosphorus availability; a strong productivity bottleneck emerges when oxygenic photosynthesis and nitrogen fixation evolve before the accumulation of significant surface phosphorus reservoirs. This bottleneck is perpetuated by strong ocean redox stratification and efficient phosphorus sequestration, which limit primary productivity and hence oxygen accumulation.This article is part of the discussion meeting issue 'Chance and purpose in the evolution of biospheres'.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| 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".