What triggered one of the most dramatic changes in Earth’s history? The ups and downs of oxygen

Amazing stuff!

"... For its first 2 billion years, Earth had almost no free oxygen in its air or oceans. Then, some 2.45 billion years ago, the ancestors of photosynthetic cyanobacteria began to flood the world with oxygen, creating the conditions that allowed complex life to evolve and prosper. The Great Oxidation Event (GOE), as it’s known, is “the most fascinating and most dramatic change in how the Earth’s surface works in its history,”

But that story has clouded recently. Mineral analyses suggest oxygen-producing microbes evolved hundreds of millions of years before the GOE, leaving a huge, unexplained gap when oxygen remained low. And the GOE appears to have been not one event but several, with oxygen repeatedly rising and falling over a span of some 200 million years—a great oxidation followed by a great deoxidation, and then back again, several times. 

Now, possible explanations are emerging.

One talk at the Goldschmidt conference this month proposed that oxygen could not rise until extensive shallow areas formed in the world’s oceans.

Another argued the oxygen pulses reflect ancient Earth’s periodic transformation into Snowball Earth, when ice engulfed the planet to low latitudes. 

Yet a study last year in Nature reported carbonate deposits created by oxygen-producing cyanobacteria 2.85 billion years ago. Using the mutation rates of modern-day microbes to date the origin of photosynthesis pushed it back even further, to as much as 3.5 billion years ago. And for 2 decades, researchers have tracked what appear to be “whiffs” of oxygen prior to the GOE, recorded in minerals that require oxygen to form. ..."

From the abstract of the oral presentation:

"The rise of atmospheric oxygen and the onset of Paleoproterozoic glaciations are commonly attributed to biological innovation, particularly the emergence of oxygenic photosynthesis. Yet geochemical evidence indicates that oxygen production predated the permanent rise of atmospheric O₂, implying that biological capability alone was insufficient to drive sustained oxygenation. Here we present results from a coupled ocean–atmosphere box model demonstrating that continental growth and shelf emergence acted as tectonic gatekeepers of long-term atmospheric redox evolution.

We introduce the concept of a continental oxygen inventory, defined as the product of shallow continental shelf area and dissolved oxygen concentration, to quantify the spatial constraint on oxygen export from the ocean to the atmosphere. Model results reveal two critical thresholds.

When the relative inventory exceeds ~0.01% of its modern value, atmospheric O₂ surpasses the mass-independent sulfur fractionation (S-MIF) threshold (~10⁻⁵ PAL).

When it exceeds ~1%, enhanced methane oxidation drives atmospheric CH₄ collapse, triggering global glaciation. Below these thresholds, even oxygenated surface waters fail to oxygenate the atmosphere.

Because shelf area is ultimately controlled by continental crust volume, mantle thermal state, plate mobility, and hypsometry, these results imply that deep Earth processes fundamentally regulated the timing and magnitude of atmospheric oxygenation. The Great Oxidation Event, therefore reflects not solely biological innovation but the progressive expansion of oxygen-producing habitats enabled by tectonic evolution during late Archean–early Proterozoic continental growth.

More broadly, this work highlights tectonics as a first-order control on planetary oxidation state and climate stability. By linking mantle dynamics to atmospheric composition through evolving continental geometry, our framework reframes Earth’s oxygenation as a coupled deep Earth–surface process. These findings have implications not only for interpreting the tempo of Earth’s environmental and biological evolution, but also for assessing the likelihood of atmospheric oxygen accumulation—and thus detectable biosignatures—on rocky exoplanets with differing tectonic regimes."

What triggered one of the most dramatic changes in Earth’s history? | Science | AAAS

Continental Growth as a Tectonic Gatekeeper of Early Earth Oxygenation (an oral presentation)

Bacteria ‘breathed’ oxygen nearly a billion years before the Great Oxidation Event

Amazing stuff!

"Aerobic respiration—using oxygen to power the process of producing cellular fuel—was a huge development for life on Earth. After some microbes figured out photosynthesis, levels of oxygen in the atmosphere jumped dramatically, resulting in what’s commonly called the Great Oxygenation Event some 2.3 billion years ago, paving the way for oxygen-breathing life to take over. But it’s never been clear when the ability to metabolize oxygen evolved. Now, thanks to a combination of fossil, genetic, and geological data, researchers have a new estimate— and it’s 900 million years before photosynthesis pumped oxygen into the atmosphere. 

..."

From the editor's summary and abstract:

"Editor’s summary

When exploring deep time, the problem is that there are few, if any, good fossils of the earliest living organisms, and it is impossible to precisely date the evolution of those that do exist.

One calibration point is provided by the impact event about 4.5 billion years ago that resulted in sterilization of Earth and formation of the Moon. Davín et al. used molecular clocks, machine learning, and phylogenetic reconciliation to present a reconstruction of the evolution of Earth’s bacterial biosphere over the past 4 billion years with particular emphasis on aerobic metabolisms. Their analysis showed that the last common ancestor of bacteria likely existed 4.4 to 3.9 billion years ago, and aerobic organisms likely emerged before the Great Oxidation Event (2.43 to 2.33 billion years ago). Oxygen tolerance may have been a prerequisite for, rather than a consequence of, the evolution of oxygenic photosynthesis. ...

Structured Abstract

INTRODUCTION

Microbial life dominates the biosphere, but a timescale of early microbial evolution has proven elusive as a result of an inadequate fossil record. The lack of maximum age calibrations—the earliest point in time at which a given group might have emerged—is particularly problematic.

However, the geochemical record bears the imprint of microbial metabolism through time, providing a complementary source of information.

A pivotal event in this history was the Great Oxidation Event (GOE) ~2.43 to 2.33 billion years ago (Ga), which marked a substantial increase in atmospheric oxygen.

This transition, driven by the evolution of cyanobacterial oxygenic photosynthesis and carbon burial, transformed the biosphere from predominantly anoxic to oxic, causing widespread adaptation to oxygen. In this study, we used the temporal link between atmospheric oxygenation and the evolutionary spread of aerobic metabolism to calibrate the phylogeny of the bacterial domain.

RATIONALE

To date the bacterial tree, we introduced multiple new maximum age calibrations by linking the GOE to the age of aerobic lineages. We used a Bayesian approach that assumes that aerobic nodes are unlikely to be older than the GOE but can predate it given sufficient evidence from fossils or sequence divergence. To implement this approach, we integrated phylogenetic reconciliation with machine learning to map transitions from anaerobic to aerobic lifestyles onto the bacterial tree. By aggregating signals across the genome, we could robustly infer aerobic and anaerobic phenotypes from incomplete ancestral gene repertoires.

RESULTS

We identified 84 anaerobic to aerobic transitions on a species tree of 1007 bacteria. Most transitions occurred after the GOE and were driven by horizontal acquisition of respiratory and oxygen tolerance genes.

However, despite the GOE calibration, at least three transitions predated this event, suggesting that aerobic respiration evolved before widespread atmospheric oxygenation and may have facilitated the evolution of oxygenic photosynthesis in cyanobacteria.

Our molecular clock analyses estimated that the last bacterial common ancestor lived in the Hadean or earliest Archaean era (4.4 to 3.9 Ga), whereas bacterial phyla originated in the Archaean and Proterozoic eras (2.5 to 1.8 Ga); most bacterial families are as old as land plants and animal phyla, dating back to the late Proterozoic (0.6 to 0.75 Ga).

CONCLUSION

We infer that the earliest aerobic bacteria emerged in the Archaean, predating the GOE by 900 million years. After the GOE, aerobic lineages experienced faster diversification than their anaerobic counterparts, highlighting the impact of atmospheric oxygenation on bacterial evolution. The approach developed here provides a framework for linking microbial traits to Earth’s geochemical history, offering a pathway for exploring the evolution of other phenotypes in the context of Earth’s history."

ScienceAdviser

A geological timescale for bacterial evolution and oxygen adaptation

An integrated approach to date bacterial evolution and reconstruct the history of oxygen adaptation.

How “Great” Was the Great Oxygenation Event?

Very recommendable! Amazing stuff! Great phylogenetics research!

"Around 2.5 billion years ago, our planet experienced what was possibly the greatest change in its history: According to the geological record, molecular oxygen suddenly went from nonexistent to becoming freely available everywhere. ...
The question that has not been resolved, however, is: Did the production of oxygen coincide with the GOE [Great Oxygenation Event], or did living organisms have access to oxygen even before that event? ...
o begin the study, Jabłońska sorted through around 130 known families of enzymes that either make or use oxygen in bacteria and archaea – the sorts of life forms that would have been around in the Archean Eon (the period between the emergence of life, ca. 4 billion years ago, and the GOE). From these she selected around half, in which oxygen-using or -emitting activity was found in most or all of the family members and seemed to be the founding function. That is, the very first family member would have emerged as an oxygen enzyme. From these, she selected 36 whose evolutionary history could be traced conclusively. ...
The phylogenetic trees the researchers ultimately obtained showed a burst of oxygen-based enzyme evolution about 3 billion years ago – something like half a billion years before the GOE. ..."

"... However, the degree to which oxygen was available to life before oxygenation of the atmosphere remains unknown. Here, phylogenetic analysis of all known oxygen-utilizing and -producing enzymes (O2-enzymes) indicates that oxygen became widely available to living organisms well before the Great Oxidation Event. About 60% of the O2-enzyme families whose birth can be dated appear to have emerged at the separation of terrestrial and marine bacteria (22 families, compared to two families assigned to the last universal common ancestor). This node, dubbed the last universal oxygen ancestor, coincides with a burst of emergence of both oxygenases and other oxidoreductases, thus suggesting a wider availability of oxygen around 3.1 Ga. [Gigaannum 10^9]"

How “Great” Was the Great Oxygenation Event?

Here is the link to the referenced paper:

The evolution of oxygen-utilizing enzymes suggests early biosphere oxygenation (behind paywall)

The researchers at the coffee table with pencil and notebooks (almost quaint)? 😄