These GEITP pages have often discussed events during evolution — which in fact occurs because of gene-environment interactions. Once the original nucleic acid formed “the first gene” (more than 4 billion years ago), all genes ever since have diverged and mutated in response to environmental and climate changes — in order to improve survival (i.e. need to find food, avoid predators, and reproduce) of the species. Carbon dioxide (CO2) and atmospheric oxygen (O2) are two gases essential for aerobic life on Earth. [This fact flies in the face of today’s eco-environmentalists — who erroneously claim that existing levels of CO2 are undesirable and dangerous.] These two gases are linked via photosynthesis: CO2 + H2O = CH2O + O2
This important link between CO2 and O2 is evident in the geological record from association of the most dramatic events in the histories of both gases. The Great Oxidation Event (GOE) — during which time Earth’s O2 levels increased by several orders of magnitude — and the Lomagundi event (LE) — when carbon-isotope ratios of marine carbonates [(CO2-)3 and (C=O)(O-)2] increased as much as ~10% — both occurred between ~2.5 and ~2.0 billion years ago. The temporal association of the two events suggests that both may be attributed to a single mechanism, such as enhanced organic carbon (organic C) burial; this is because increasing the fraction of carbon buried as organic C (forg), relative to carbonate, will increase the amount of O2 that is produced and allowed to accumulate (CO2 + H2O = CH2O + O2).
Despite the apparent temporal association of the GOE and LE, and the conceptual consistency of explaining both events via increased forg, its role as the driver of the GOE and LE remains uncertain. There is evidence that photosynthesis evolved at least a half billion years before the GOE, so why would O2 have remained low for so long?. In addition, other studies have suggested that the GOE may have preceded the LE by ~100 million years. If the onset times of the GOE and LE were indeed temporally different — it becomes difficult to explain both events via a single mechanism; this has led researchers to propose mechanisms invoking decreased sinks of O2 as the main driver of the GOE. Whereas decreased O2 sinks would allow atmospheric O2 to accumulate, it is unclear how they would drive the associated positive C-isotope excursion.
Authors [see attached article] propose a single mechanism for the GOE and LE. Modeling shows that their proposed mechanism can simultaneously explain both increased O2 production and a positive C-isotope excursion in marine carbonates. Authors show that their proposed mechanism is consistent with a delay between the evolution of photosynthesis and increased O2 levels, as well
as a delay between the build-up of O2 in the atmosphere, and the positive C-isotope excursion observed in marine carbonates.
Authors demonstrate that ~2.5 billion years ago, a tectonic transition — that resulted in increased volcanic CO2 emissions could have led to increased deposition of both carbonates and organic C via enhanced weathering and nutrient delivery to oceans. Increased burial of carbonates and organic C would have allowed the accumulation of atmospheric O2 while also increasing the delivery of carbon to subduction zones. Coupled with preferential release of carbonates at arc volcanoes, and deep recycling of organic C to ocean island volcanoes, authors report that such a tectonic transition can simultaneously explain the Great Oxidation Event and the Lomagundi Event — without any change in fraction of carbon buried as organic C relative to carbonate (which is often invoked to explain carbon isotope excursions). Authors therefore suggest that the first substantial burst of O2 on Earth was added by a wave of volcanic eruptions — brought about by tectonic plate movements. Their study offers a new theory to help explain the Great Oxidation Event of ~2.5 billion years ago, from which Earth began an explosion of evolution of many aerobic-metabolism organisms — in addition to the predominance of anaerobic metabolic organisms from ~4.2 billion to ~2.5 billion years ago. 😊
DwN
Nature Geoscience; Dec 2019; https://doi.org/10.1038/s41561-019-0492-6