# Dating the evolution of oxygenic photosynthesis using La-Ce geochronology

Laureline A Patry, Pierre Bonnand, Maud Boyet, Munira Afroz, Dylan T Wilmeth, Brittany Ramsay, Philippe Nonnotte, Martin Homann, Pierre Sansjofre, Philip W Fralick, et al.

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To cite this version:

Laureline A Patry, Pierre Bonnand, Maud Boyet, Munira Afroz, Dylan T Wilmeth, et al. Dating the evolution of oxygenic photosynthesis using La-Ce geochronology. Nature, 2025, 642, pp.99-104. 10.1038/s41586-025-09009-8. hal-05057809

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Dating the evolution of oxygenic
photosynthesis using La-Ce
geochronology

Laureline A. Patry<fnref n="1" />, Pierre Bonnand<fnref n="1" />*, Maud Boyet<fnref n="2" />, Munira Afroz<fnref n="1" />, Dylan T. Wilmeth<fnref n="1" />†, Brittany Ramsay<fnref n="3" />‡, Philippe Nonnotte<fnref n="1" />, Martin Homann<fnref n="4" />, Pierre Sansjofre<fnref n="5" />, Philip W. Fralick<fnref n="3" />, and Stefan V. Lalonde<fnref n="1" />*

<footnote n="1">¹ Laboratoire Geo-Ocean, CNRS, Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, 29280 Plouzané, France</footnote>

<footnote n="2">² Laboratoire Magmas et Volcans, CNRS, Université Clermont Auvergne, 63178 Aubière, France</footnote>

<footnote n="3">³ Department of Geology, Lakehead University, Thunder Bay, P7B 5E1 Ontario, Canada</footnote>

<footnote n="4">⁴ Department of Earth Sciences, University College London, WC1E 6BS London, United Kingdom</footnote>

<footnote n="5">⁵ Muséum National d’Histoire Naturelle, UMR7590 IMPMC, 75005 Paris, France</footnote>

<footnote>* Corresponding Authors: pierre.bonnand@univ-brest.fr and stefan.lalonde@univ-brest.fr</footnote>

<footnote>† Current address: Geology Department, Grand Valley State University, 49401 Allendale, Michigan, U.S.A.</footnote>

<footnote>‡ Current address: Department of Geological Sciences and Geological Engineering, Queens University, Kingston, K7L 3N6 Ontario, Canada</footnote>
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There is ongoing debate as to when oxygenic photosynthesis evolved on Earth¹,².
Geochemical data from ancient sediments indicate localised or ephemeral photosynthetic O₂
production prior to Great Oxidation Event (GOE) ca. 2.5-2.3 billion years (Ga) ago, and
currently suggest Archean origins, approximately 3 Ga ago or earlier³⁻⁹. However, sedimentary
records of the early Earth often suffer from preservation issues, and poor control on the timing
of oxidation leaves geochemical proxy data for the ancient presence of O₂ open to critique¹⁰⁻¹³.

Here we report rare earth element data from three different Archean carbonate platforms preserved in greenstone belts of the NW Superior Craton (Canada) that were deposited by the activity of marine photosynthetic bacteria at 2.87 Ga, 2.85 Ga, and 2.78 Ga. All three indicate O₂ production before the GOE in the form of significant depletions in cerium (Ce), reflecting oxidative Ce removal from ancient seawater, as occurs today¹⁴. Using ¹³⁸La-¹³⁸Ce geochronology, we show that La/Ce fractionation, and thus Ce oxidation, occurred at the time of deposition, making these the oldest directly dated Ce anomalies. These results place the origin of oxygenic photosynthesis in the Mesoarchean or earlier and bring important new perspective on a long-standing debate regarding Earth's biological and geochemical evolution.
## Main text

While the significant accumulation of atmospheric oxygen during the ca. 2.5 to 2.3 Ga Great Oxygenation Event (GOE) places a later bound on the evolution of oxygenic photosynthesis, its earlier bound is poorly constrained. For more than a decade now, geochemical data from Precambrian sedimentary records world-wide have indicated the establishment of both marine and lacustrine “O₂ oases” prior to the GOE, where O₂ was locally and/or ephemerally produced by oxygenic photosynthesis under otherwise anoxic atmospheric conditions between 2.5 and 3.0 Ga³⁻⁹, and perhaps as far back as 3.8 Ga¹⁵. Theoretical considerations support the development of pelagic¹⁶ and benthic¹⁷ O₂ oases where open ocean, shallow-water, and terrestrial O₂-producing microbial communities may have thrived for hundreds of millions of years before having any significant effect on atmospheric O₂ contents. Molecular clock analyses also support a relatively early origin of oxygenic photosynthesis between 3.6 and 2.8 Ga¹⁸⁻²⁰ but estimates may vary widely, from 4.5 Ga to 2.32 Ga²¹. Without unambiguous evidence at present of oxygenic photosynthesis during the Archean in the form of cyanobacterial microfossils²² or biomarkers²³, recognising whether free O₂ was being biologically produced in deep geological time depends largely on geochemical and isotopic proxy data from Precambrian sedimentary rocks.

However, the primary nature of geochemical signals of early photosynthetic O₂ production on Earth is often questionable given the diverse diagenetic, metamorphic, hydrothermal, and surface oxidative weathering processes that affect the Precambrian sedimentary record. The issue of syngenicity is particularly problematic for sensitive trace metal and metal isotope redox proxies in sedimentary sequences of paleobiological interest have been exposed to oxygen-rich surface conditions for millions of years or more. On one hand, since Anbar et al.'s seminal oxygen whiff paper³, the body of work presenting trace element or stable isotope evidence for transient free oxygen production prior to the GOE continues to grow⁴,⁵,⁷⁻⁹,²⁴. On the other hand, follow-up work has revealed significant concerns regarding the syngenetic nature of some of these signals, whether by the fact that they may be present in surface samples but absent in drill core¹⁰⁻¹², or more controversially, that remobilisation and concentration in later phases of mineralisation affected certain proxy signals¹³, although there are multiple lines of evidence to the contrary²⁵. As a result, there is significant uncertainty as to the timing of the origin of oxygenic photosynthesis on Earth.

With these issues in mind, we examined multiple carbonate platforms of the Northwest Superior craton for geochemical evidence of Archean photosynthetic O₂ production. All three
sites show unambiguous fossil evidence for photosynthetic bacterial influence by the abundant
carbonate microbialites they preserve (Figure 1). Fresh carbonate samples from the 2.87 Ga
Red Lake Greenstone Belt<sup>26-28</sup>, 2.85 Ga Woman Lake Assemblage<sup>26,29</sup>, and 2.78 Ga Steep Rock
Group<sup>5,30</sup> were collected from PQ-size industry drill core (Red Lake), short NQ-size backpack
drill cores (Red Lake, Woman Lake), and from outcrop at recent exposures (Woman Lake,
Steep Rock) and analysed for their major element, trace element, and Ce isotope compositions.

Dominated by recrystallized stromatolitic dolostones, microbialitic and aragonite-crystal-fan
limestones, and associated clastic and chemical sediments (Figure 1), these little-explored
northern Canadian fossilised microbial ecosystems exemplify the trend of increasing thickness
in Earth's known sedimentary carbonate deposits throughout the Archean<sup>5</sup>. Outcrops often
show glacial striations due to their recent surface exposure after the last glacial maxima ca.
20,000 years before present, making these sites excellent targets for Precambrian paleoredox
investigations as they have experienced minimal modern surface weathering.

Post-Archean Australian Shale (PAAS)-normalised REE data for weak leach digestions of highly pure carbonate samples from all three sites demonstrate their marine sedimentary origin via characteristic positive anomalies in La and Gd, high Y/Ho, as well as heavy REE (HREE) enrichment, and their open-ocean connection is further supported by the presence of positive Eu anomalies characteristic of Archean hydrothermally influenced seawater (Figure 2, Supplementary Tables 1 and 2). Cerium is unique amongst REE in that oxidation of Ce(III) to Ce(IV) under mildly oxidising conditions and enhanced particle scavenging of Ce(IV) to organic and mineral surfaces³¹ generate characteristic positive and negative Ce anomalies in shale-normalised REE spectra in marine chemical sediments deposited from oxygenated seawater³². Importantly, samples from all three sites show variable degrees of Ce depletion, with negative Ce anomalies (Ce/Ce* calculated using the geometric projection from Pr and Nd³³) as low as 0.79 at Red Lake, 0.46 at Woman Lake, and 0.38 at Steep Rock. These anomalies, some comparable in magnitude to those found in modern oxygenated seawater (mean Ce/Ce* of 0.36 above 400 m depth as compiled by ref. 34), are some of the largest yet described for Precambrian sediments.

The only process known to generate such large Ce anomalies is the oxidation of Ce(III) to
Ce(IV) in the presence of free O₂. The oxidation of Ce in aqueous solution occurs at a redox
potential close to the Mn(II)/Mn(IV) couple, but appears highly sensitive to the presence of
diverse ligands, and is significantly lowered in the presence of Mn oxides upon which oxidation
is surface-catalysed³⁵,³⁶. Even in modern oxygenated seawater, oxidation is rarely complete¹⁴,
as Ce oxidation is limited by kinetic factors. Under high-pH conditions such as in alkaline
lakes, Ce oxidation is significantly accelerated³⁷, whereas at the circumneutral pH of rivers and seawater, oxidation is slow, and largely driven by catalysis at mineral surfaces. Indeed, rivers today transport predominately Ce(III) and generally lack significant Ce anomalies except at unusually high pH³⁸. Upon oxidation, the resulting Ce(IV) is less soluble than trivalent REE and rapidly scavenged from solution by surface adsorption onto sinking organic matter, clays, and Fe- and Mn-oxides. To generate such significant negative Ce anomalies in natural waters similar to those reported here, several criteria must be met. Physically, particulates bearing surface-adsorbed Ce(IV) must be isolated from their formation waters in order for the latter to develop an anomaly in the residual aqueous phase; remineralisation of potential Ce(IV) carriers (organic matter, Mn and Fe oxyhydroxides) may act to prevent efficient sequestration of Ce(IV) from Ce(III)³⁹. Furthermore, Ce(IV) oxidation rates are generally slow compared to Ce(III) scavenging rates in shallow-water marine environments, and only in waters poor in settling particulate matter does the Ce(IV) oxidation rate become important relative to the rate of Ce(III) removal, which is also governed by adsorption⁴⁰. Thus, Ce oxidation may be cryptic in shallow-water or particulate-rich environments, whereas the development of notable water column Ce anomalies is favoured in offshore environments with slower scavenging of trivalent REE. This modern observation is particularly pertinent for Archean depositional environments where Ce(III) scavenging prevailed and Ce(IV) oxidation was minimal in most depositional environments.

Several Ce(III) oxidation pathways are possible, however only a few are relevant to the Precambrian. Firstly, H₂O₂ is an efficient Ce(III) oxidant, however its photochemical production in the Archean atmosphere is thought to have been insignificant relative to other potential oxidants⁴¹, which include Fe(III), O(-II), and Mn(IV). While appreciable Ce anomalies have been generated by adsorption to iron oxyhydroxides under experimental conditions³¹, Archean seawater appears to have been ferruginous in nearly all settings, and was likely buffered around the relatively low redox potential set by the Fe(II)/Fe(III) couple. The rock record itself further indicates that Ce(III) oxidation by Fe(III) was negligible relative to Ce(III) scavenging during much of the Archean, as banded iron formations generally do not show important Ce anomalies until ca. 2.46 Ga⁴². At this time, mild but appreciable sedimentary Ce anomalies become widespread, often in association with sedimentary Mn enrichments, reflecting a more permanent establishment of O₂-bearing surface waters in the global ocean redox environment in the wake of the GOE⁴³,⁴⁴. However, as elaborated below, even the most immobile and well-understood redox tracers – such as the presence of Ce anomalies – may be subject to false positives for ancient O₂ as the result of the complex
alteration histories of such highly ancient sediments<sup>12,45,46</sup>. This problem is arguably the
principal issue currently limiting our understanding of when oxygenic photosynthesis evolved.

Recent advances in radiometric isotope geochemistry offer a promising solution to this problem. At least three currently applied redox tracers (based on U, Re, and Ce) form radiogenic parent-daughter pairs that can be used to date the closure of their radioisotope systems on time scales suitable for ancient Earth studies; however, few examples of such applications exist at present. An analysis of the U-Th-Pb systematics of basalt samples from drill core recovered from over 100 m depth in the Marble Bar region of the Pilbara Craton, Northwestern Australia, revealed that the hematite present is due to later alteration of the basalts by oxidising fluids<sup>47</sup>, and not the presence of an Archean O<sub>2</sub>-bearing atmosphere, as previously suggested<sup>48</sup>. In the late Archean Mount McRae Shale from Western Australia, where a pre-GOE oxygen oasis was previously identified<sup>3</sup> and since supported by multiple lines of evidence, including stratigraphic trends in Mo, U, Se, as well as S and N (see synthesis by ref. 49), Re-Os systematics indicate the onset, and then termination, of a transient episode of pre-GOE oxidative continental weathering ca. 2.495 Ga in a unique case where Re-Os isotopic closure is effectively demonstrated to be near syn-depositional<sup>49</sup>.

The La-Ce system is similarly capable of anchoring La-Ce separation processes, and thus redox reactions, in geological time<sup>50-52</sup>. In the La-Ce system, <sup>138</sup>La decays via two parallel processes: 34.8% of the isotope undergoes β<sup>-</sup> decay to stable <sup>138</sup>Ce, while the remaining 65.2% disintegrates by electron capture, forming stable <sup>138</sup>Ba (ref. 53). The long half-life (t<sup>1/2</sup> = 1.036 ± 0.02 x 10<sup>11</sup> years, 1σ)<sup>53</sup> and the low natural abundance (0.089%) of <sup>138</sup>La generates only very small variations in <sup>138</sup>Ce/<sup>142</sup>Ce compared to other radiogenic isotope systems<sup>54</sup>. Furthermore, the high abundance of <sup>140</sup>Ce, about 400 times more abundant than the isotopes <sup>136</sup>Ce and <sup>138</sup>Ce, as well as multiple potential isobaric interferences from Ba, renders Ce isotopic analysis particularly challenging.

Although <sup>138</sup>Ce/<sup>142</sup>Ce variations are small in nature and their measurement requires particularly efficient chemical purification and high analytical precision, this system is nonetheless highly promising for determining the closure age of the La-Ce system and thus the age of generation of Ce anomalies driven by redox processes. Hayashi et al.<sup>45</sup> were the first to analyse the La-Ce isotope systematics of ancient sediments, showing that in the 3.3 Ga Fig Tree and 3.2 Ga Moodies Groups of the Barberton Greenstone Belt, South Africa, the observed negative Ce anomalies could not be primary, but rather were generated during episodes of alteration that took place sometime in the past 1.1 Ga. More recently, Bonnand et al.<sup>46</sup>
constrained the timing of Ce anomalies in 3.2 Ga BIF from the Moodies Group to the last 100
million years using the La-Ce geochronometer, generating an isochron of 60 ± 32 Ma that
unquestionably confirmed that these anomalies are secondary artefacts of Phanerozoic surface
alteration.

To constrain the origin of Ce anomalies in the Archean carbonate platforms studied
here<sup>5,23,25</sup>, a subset of samples were analysed for their La-Ce isotope compositions
(Supplementary Table 3). The samples of this subset were selected to generate a maximum
range in La/Ce (which inherently included those samples showing the most significant Ce
anomalies) as well as consistent spacing in their La/Ce values, minimal concentrations in
detrital-sourced elements such as Al and Ti (&lt;1% and 0.1%, respectively), and more arbitrarily,
on the basis of a visual and numeric assessment of their REE spectral features (e.g., non-flat
slopes and clear seawater signatures). The Ce/Ce* values in this subset range from 0.79 to 1.02
for Red Lake, 0.46 to 0.74 for Woman Lake, and 0.38 to 0.84 for Steep Rock. Plotting the
<sup>138</sup>La/<sup>142</sup>Ce vs. <sup>138</sup>Ce/<sup>142</sup>Ce isotope compositions together from the three sites is highly
informative (Extended Data Figure 1). The 18 samples analysed across the three sites have
<sup>138</sup>La/<sup>142</sup>Ce ratios ranging from 0.005 to 0.030 and <sup>138</sup>Ce/<sup>142</sup>Ce ratios ranging from 0.0225796
to 0.0227409. These 18 values form a slope of 0.007353 ± 0.00127 (MSWD = 48.2) with a
corresponding La-Ce age of 3125 ± 536 Ma and an ε<sup>138</sup>Ce<sub>initial</sub> = -1.89 ± 5.80. When 4 outliers
are removed, the remaining 14 values form a slope of 0.006357 ± 0.00024 (MSWD = 1.99)
with a corresponding La-Ce age of 2706 ± 102 Ma and an ε<sup>138</sup>Ce<sub>initial</sub> = 1.45 ± 0.74. The data
point toward an initial <sup>138</sup>Ce/<sup>142</sup>Ce ratio that is close to that of CHUR (Extended Data Figure
1), as expected for a crustal REE source ca. 3 Ga, and the negative Ce anomalies observed in
these Archean carbonate samples are clearly very ancient.

The data from the three different sites form three distinct individual isochrons (Figure 3).
The Red Lake samples (without outliers, n=5) form a slope of 0.006823 ± 0.000422 (MSWD = 0.19) with a corresponding age of 2902 ± 178 Ma and an ε¹³⁸Ceinitial of 0.77 ± 1.38 (Figure 3a). The Woman Lake samples (without outliers, n=4) form a slope of 0.006574 ± 0.000411 (MSWD = 1.38) with a corresponding age of 2797 ± 173 Ma and ε¹³⁸Ceinitial of -0.06 ± 2.48 (Figure 3b). The Steep Rock samples (n=5) form a slope of 0.006430 ± 0.000349 (MSWD = 1.07) with a corresponding La-Ce age of 2736 ± 147 Ma and ε¹³⁸Ceinitial of 0.72 ± 2.13 (Figure 3c). Crucially, all three La-Ce isochrons provide ages that overlap within error with the minimum depositional ages determined independently by zircon U-Pb geochronology (Extended Data Figure 2), which are 2873 ± 7 Ma for Red Lake, 2846 ± 5 Ma for Woman
Lake, and 2780 ± 1 Ma for Steep Rock⁵⁵. Using the best currently available estimates of the
¹³⁸La β⁻ and β⁺ decay constants and their uncertainties (see Methods), the La-Ce closure ages
are resolved from the GOE for all the three sites, with 2s uncertainty limits that are no younger
than 2724 Ma, 2624 Ma, and 2589 Ma for Red Lake, Woman Lake, and Steep Rock,
respectively. These become 2619 Ma, 2522 Ma, and 2489 Ma, respectively, at the uppermost
2s limit of the ¹³⁸La β⁻ decay constant. The joint probability that all three signals can be
explained by Ce oxidation sometime after 2.5 Ga is ruled out to better than 3.5 sigma even if
we doubled our analytical uncertainty (see Extended Data Figure 2 and Supplementary
Information). These data strongly indicate a syn-depositional origin for the reported La/Ce
fractionations (and thus Ce anomalies).

The direct geochronological evidence we present for an ancient, pre-GOE origin of
negative Ce anomalies has important implications for our understanding of the timing of the
evolution of oxygenic photosynthesis and the early evolution of biogeochemical cycles. Firstly,
at all three sites, the presence of negative Ce anomalies was far from universal across the
hundreds of samples analysed from these sites for their REE systematics. Indeed, at Red Lake,
only a small number (<20) of samples showed significant negative Ce anomalies, and the vast
majority came from one site in particular, at the Golden Arm site where m-scale limestone
domes comprised of crystal fans underlain by carbonate microbialite outcrop at the lakeshore.
This indicates that even at Archean sites where oxygenic photosynthesis is likely to have been
occurring, sedimentary trace element and isotopic signals for the presence of O₂ may be rare.
This is not surprising for the Ce redox proxy considering that even in modern shallow-water
environments with abundant water column O₂, Ce(III) oxidation rates may be slow, and only
in more open-ocean settings where flocculating particulate concentrations reach a minimum
does the Ce(III) oxidation rate exceed the Ce(III) turnover time and permit the water column
expression of significant Ce anomalies⁴⁰. In other words, it is unlikely that O₂ production was
restricted to deeper water environments, but rather it is only where REE residence times were
sufficiently long that a significant Ce(IV) reservoir could accumulate in the face of sluggish
Ce(III) oxidation kinetics and generate Ce anomalies as large as those reported here. It also
means that early oxygenic photosynthesis may be cryptic for a variety of proxies where local
effects, competing reactions, and kinetic factors may strongly impact the expression of
oxidative signals.

This work adds significant support to over a decade of previous work suggesting such
ancient O₂ production. More importantly, our results provide a critical chronological anchor
point in deep geological time that places a lower bound on the evolution of oxygenic photosynthesis. Such anchor points are vital for phylogenetic molecular clock reconstructions of the evolution of early microbial metabolisms, yet efforts to date have yielded differing conclusions regarding the origin of oxygenic photosynthesis. This is suggested by some studies to have occurred within 100 Ma or so of the GOE itself⁵⁶,⁵⁷, and thus its evolution may coincide with the GOE itself, whereas others place the evolution of oxygenic photosynthesis hundreds-of-millions to a billion years earlier¹⁸⁻²⁰. The data presented here provide strong geological support for the latter, and should enable a new generation of molecular clock reconstructions, as well as geochronologically supported paleoredox studies of Earth's most ancient sediments, to better address this question. The Mesoarchean anchor point of 2.87 Ga for the operation of oxygenic photosynthesis indicated by our data should stimulate further research and insight into the evolution of Earth's most important microbial metabolism.

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References

1. Cardona, T. Thinking twice about the evolution of photosynthesis. *Open Biol* **9**, 180246 (2019).

2. Sánchez-Baracaldo, P. & Cardona, T. On the origin of oxygenic photosynthesis and Cyanobacteria. *New Phytol.* **225**, 1440–1446 (2020).

3. Anbar, A. D. et al. A Whiff of Oxygen Before the Great Oxidation Event? *Science* **317**, 1903–1906 (2007).

4. Planavsky, N. J. et al. Evidence for oxygenic photosynthesis half a billion years before the Great Oxidation Event. *Nat Geosci* **7**, 283–286 (2014).

5. Riding, R., Fralick, P. & Liang, L. Identification of an Archean marine oxygen oasis. *Precamb Res* **251**, 232–237 (2014).

6. Robbins, L. J. et al. Trace elements at the intersection of marine biological and geochemical evolution. *Earth Sci Rev* **163**, 323–348 (2016).

7. Eickmann, B. et al. Isotopic evidence for oxygenated Mesoarchaean shallow oceans. *Nat Geosci* **11**, 133–138 (2018).

8. Thoby, M. et al. Global importance of oxic molybdenum sinks prior to 2.6 Ga revealed by the Mo isotope composition of Precambrian carbonates. *Geology* **1–4** (2019).

9. Wilmeth, D. T. et al. Evidence for benthic oxygen production in Neoarchean lacustrine stromatolites. *Geology* **50**, 907–911 (2022).

10. Albut, G. et al. Modern rather than Mesoarchaean oxidative weathering responsible for the heavy stable Cr isotopic signatures of the 2.95 Ga old Ijzermijn iron formation (South Africa). *Geochim Cosmochim Ac* **228**, 157–189 (2018).

11. Albut, G. et al. Modern weathering in outcrop samples versus ancient paleoredox information in drill core samples from a Mesoarchaean marine oxygen oasis in Pongola Supergroup, South Africa. *Geochim Cosmochim Ac* **265**, 330–353 (2019).

12. Planavsky, N. J., Robbins, L. J., Kamber, B. S. & Schoenberg, R. Weathering, alteration and reconstructing Earth's oxygenation. *Interface Focus* **10**, 20190140–10 (2020).

13. Slotznick, S. P. et al. Reexamination of 2.5-Ga “whiff” of oxygen interval points to anoxic ocean before GOE. *Sci Adv* **8**, eabj7190 (2022).

14. German, C. R. & Elderfield, H. Application of the Ce anomaly as a paleoredox indicator: The ground rules. *Paleoceanography* **5**, 823–833 (1990).

15. Frei, R. et al. Oxidative elemental cycling under the low O₂ Eoarchean atmosphere. *Sci Rep* **6**, 21058 (2016).
284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

16. Olson, S. L., Kump, L. R. & Kasting, J. F. Quantifying the areal extent and dissolved oxygen concentrations of Archean oxygen oases. *Chem Geol* **362**, 35–43 (2013).

17. Lalonde, S. V. & Konhauser, K. O. Benthic perspective on Earth's oldest evidence for oxygenic photosynthesis. *Proc Nat Acad Sci USA* **112**, 201415718–1000 (2015).

18. Cardona, T., Sánchez-Baracaldo, P., Rutherford, A. W. & Larkum, A. W. Early Archean origin of Photosystem II. *Geobiology* **17**, 127–150 (2018).

19. Boden, J. S., Konhauser, K. O., Robbins, L. J. & Sánchez-Baracaldo, P. Timing the evolution of antioxidant enzymes in cyanobacteria. *Nat Commun* **12**, 4742 (2021).

20. Fournier, G. P. et al. The Archean origin of oxygenic photosynthesis and extant cyanobacterial lineages. *Proc R Soc B* **288**, 20210675 (2021).

21. Fischer, W. W., Hemp, J. & Johnson, J. E. Evolution of Oxygenic Photosynthesis. *Annu Rev Earth Planet Sci* **44**, 1–37 (2013).

22. Brasier, M. D. et al. Questioning the evidence for Earth's oldest fossils. *Nature* **416**, 76–81 (2002).

23. French, K. L. et al. Reappraisal of hydrocarbon biomarkers in Archean rocks. *Proc Nat Acad Sci USA* **112**, 5915–5920 (2015).

24. Koehler, M. C., Buick, R. B., Kipp, M. A., Stüeken, E. E. & J. Zaloumis. Transient surface oxean oxygenation recorded in the ~2.66-Ga Jeerinah Formation, Australia. *Proc Nat Acad Sci USA* **115**, 7711–7716 (2018).

25. Anbar, A. D. et al. Technical comment on “Reexamination of 2.5-Ga ‘whiff’ of oxygen interval points to anoxic ocean before GOE”. *Sci Adv* **9**, sciadv.abq3736 (2023).

26. Hofmann, H. J., Thurston, P. C. & Wallace, H. Archean stromatolites from Uchi greenstone belt, northwestern Ontario. *Geol Assoc Can Spec Pap* **28**, 125–132 (1985).

27. McIntyre, T. & Fralick, P. Sedimentology and Geochemistry of the 2930 Ma Red Lake–Wallace Lake Carbonate Platform, Western Superior Province, Canada. *Depos Rec* **3**, 258–287 (2017).

28. Afroz, M., Fralick, P. W. & Lalonde, S. V. Sedimentology and geochemistry of basinal lithofacies in the Mesoarchean (2.93 Ga) Red Lake carbonate platform, northwest Ontario, Canada. *Precamb Res* **388**, 106996 (2023).

29. Ramsay, B., Environmental Control of Seawater Geochemistry in a Mesoarchean Peritidal System, Woman Lake, Superior Province. MSc thesis, Lakehead University (2020).

30. Fralick, P. & Riding, R. Steep Rock Lake: Sedimentology and geochemistry of an Archean carbonate platform. *Earth Sci Rev* **151**, 132–175 (2015).
332

31. Bau, M. Scavenging of dissolved yttrium and rare earths by precipitating iron oxyhydroxide: experimental evidence for Ce oxidation, Y-Ho fractionation, and lanthanide tetrad effect. *Geochim Cosmochim Ac* **63**, 67–77 (1999).

333

334

335

336

32. Bau, M. & Dulski, P. Distribution of yttrium and rare-earth elements in the Penge and Kuruman iron-formations, Transvaal Supergroup, South Africa. *Precamb Res* **79**, 37–55 (1996).

337

338

339

340

33. Lawrence, M. G., Greig, A., Collerson, K. D. & Kamber, B. S. Rare Earth Element and Yttrium Variability in South East Queensland Waterways. *Aquat Geochem* **12**, 39–72 (2006).

341

342

343

344

34. Wallace, M. W. et al. Oxygenation history of the Neoproterozoic to early Phanerozoic and the rise of land plants. *Earth Planet Sc Lett* **466**, 12–19 (2017).

345

346

347

35. Sholkovitz, E. R., Landing, W. M., & Lewis, B. L. Ocean particle chemistry: The fractionation of rare earth elements between suspended particles and seawater. *Geochim Cosmochim Ac* **58**, 1567–1579 (1994).

348

349

350

351

36. Carlo, E. H. D., Wen, X.-Y. & Irving, M. The Influence of Redox Reactions on the Uptake of Dissolved Ce by Suspended Fe and Mn Oxide Particles. *Aquat Geochem* **3**, 357–389 (1997).

352

353

354

355

37. Möller, P. & Bau, M. Rare-earth patterns with positive cerium anomaly in alkaline waters from Lake Van, Turkey. *Earth Planet Sc Lett* **117**, 671–676 (1993).

356

357

358

38. Goldstein, S. J. & Jacobsen, S. B. Rare earth elements in river waters. *Earth Planet Sc Lett* **89**, 35–47 (1988).

359

360

361

39. Planavsky, N. et al. Iron-oxidizing microbial ecosystems thrived in late Paleoproterozoic redox-stratified oceans. *Earth Planet Sc Lett* **286**, 230–242 (2009).

362

363

364

40. Moffett, J. W. Microbially mediated cerium oxidation in sea water. *Nature* **345**, 421–423 (1990).

365

366

367

41. Pecoits, E. et al. Atmospheric hydrogen peroxide and Eoarchean iron formations. *Geobiology* **13**, 1–14 (2014).

368

369

370

42. Warchola, T. et al. Petrology and geochemistry of the Boolgeeda Iron Formation, Hamersley Basin, Western Australia. *Precamb Res* **316**, 155–173 (2018).

371

372

373

43. Hodgskiss, M. S. W., Lalonde, S. V., Crockford, P. W. & Hutchings, A. M. A carbonate molybdenum isotope and cerium anomaly record across the end-GOE: Local records of global oxygenation. *Geochim Cosmochim Ac* **313**, 313–339 (2021).

374

375

376

377

44. Liu, X.-M. et al. A persistently low level of atmospheric oxygen in Earth's middle age. *Nat Commun* **12**, 351 (2021).

378

379
380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

45. Hayashi, T., Tanimizu, M. & Tanaka, T. Origin of negative Ce anomalies in Barberton sedimentary rocks, deduced from La–Ce and Sm–Nd isotope systematics. *Precamb Res* **135**, 345–357 (2004).

46. Bonnand, P. et al. Post-depositional REE mobility in a Paleoarchean banded iron formation revealed by La-Ce geochronology: A cautionary tale for signals of ancient oxygenation. *Earth Planet Sc Lett* **547**, 116452–11 (2020).

47. Li, W., Johnson, C. M. & Beard, B. L. U–Th–Pb isotope data indicate phanerozoic age for oxidation of the 3.4Ga Apex Basalt. *Earth Planet Sc Lett* **319–320**, 197–206 (2012).

48. Hoashi, M. et al. Primary haematite formation in an oxygenated sea 3.46 billion years ago. *Nat Geosci* **2**, 301–306 (2009).

49. Kendall, B., Creaser, R. A., Reinhard, C. T., Lyons, T. W. & Anbar, A. D. Transient episodes of mild environmental oxygenation and oxidative continental weathering during the late Archean. *Sci Adv* **1**, e1500777 (2015).

50. Tanaka, T. & Masuda, A. The La–Ce geochronometer: a new dating method. *Nature* **300**, 515–518 (1982).

51. Dickin, A. P. La–Ce dating of Lewisian granulites to constrain the 138La β-decay half-life. *Nature* **325**, 337–338 (1987).

52. Tanimizu, M. & Tanaka, T. Origin of Elements in the Solar System, Implications of Post-1957 Observations. 555–572 (2002).

53. Bé, M.-M. et al. Table of Radionuclides (Vol. 8 – A = 41 to 198). (Bureau International des poids et mésures, Monographie BIPM-5, 2016).

54. Bonnand, P., Israel, C., Boyet, M., Doucelance, R. & Auclair, D. Radiogenic and stable Ce isotope measurements by thermal ionisation mass spectrometry. *J Anal At Spectrom* **34**, 504–516 (2019).

55. Fralick, P. et al. Earth’s earliest known extensive, thick carbonate platform suggested by new age constraints. *Earth Planet Sci Lett* **656**, 119273 (2025).

56. Soo, R. M., Hemp, J., Parks, D. H., Fischer, W. W. & Hugenholtz, P. On the origins of oxygenic photosynthesis and aerobic respiration in Cyanobacteria. *Science* **355**, 1436–1440 (2017).

57. Shih, P. M., Ward, L. M. & Fischer, W. W. Evolution of the 3-hydroxypropionate bicycle and recent transfer of anoxygenic photosynthesis into the Chloroflexi. *Proc Natl Acad Sci USA* **114**, 10749–10754 (2017).
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<figure><img src="image_3.png" /><figcaption>**Figure 1.** Archean carbonate platforms targeted by this study. (a) Map of the NW Superior Craton showing the locations of the Archean carbonate platforms examined in this study as well as representative field photographs of the stromatolitic carbonates from the three sites: (b) silicified dolomite hosting domal stromatolites in the 2.87 Ga Ball Assemblage, Red Lake Greenstone Belt, (c) calcitic domal bioherm with columnar stromatolites overlain by grainstone in the 2.85 Ga Woman Lake Assemblage, and (d) bioherm composed of laterally linked stromatolite domes in the 2.78 Steep Rock Group.</figcaption></figure>

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<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /><figcaption>**Figure 2.** REE data reveal important negative Ce anomalies in Archean carbonates from the Superior Craton. PAAS-normalised REE spectra of samples analysed for La-Ce isotope systematics (individual spectra) compared to larger REE datasets (shaded areas) for Archean carbonate samples from Red Lake (a), Woman Lake (b) and Steep Rock (c). The larger REE datasets include data from Ramsay (2020) and Afroz et al. (2023) that were generated using identical methods in the same facilities (see Methods).</figcaption></figure>
<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

**Figure 3.** La-Ce geochronology demonstrating Archean-age Ce anomalies. <sup>138</sup>La-<sup>138</sup>Ce isochrons and corresponding La-Ce closure ages for Ce-anomaly-bearing carbonate rocks from (a) Red Lake, (b) Woman Lake, and (c) Steep Rock. Their minimum depositional ages, constrained independently by zircon U-Pb geochronology, are 2873 ± 7 Ma, 2846 ± 5 Ma, and 2780 ± 1Ma, respectively (see main text). Uncertainties on the data points (coloured ellipses) and isochron regressions (grey shaded areas) are represented as 95% confidence intervals.

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# Methods

## Sample preparation and pre-screening

Whole rock samples were cut by diamond saw to exclude any veins and remove exterior surfaces that were in contact with the surface weathering environment or with the core drill bit where applicable, and surfaces in contact with the diamond saw were abraded using corundum paper. Samples were then rinsed in distilled water, air-dried, crushed in a high purity tungsten carbide cylinder, and powdered in an agate ring mill. All further preparations were conducted in a class 1000 clean lab at the Pôle Spectrométrie Océan using high-purity acids (trace-metal grade or PFA-distilled in-house). For trace element analyses, ~50 mg of powder was leached overnight at room temperature in 8 ml PFA vials in 2 ml of 5% trace-metal-grade acetic acid, as per ref. 58 and similar to ref. 59 but at slightly higher acetic acid concentrations and without pre-leaching. Trace elements were analysed on aliquots diluted 50X in 2% HNO₃ containing 2 ppb In for drift correction using a ThermoFisher ElementXR high-resolution ICP-MS operating in low, medium, and high-resolution mode. The instrument was tuned for minimal oxide production, which was further constrained by analysis of mono-elemental solutions of Ba and Nd, and no oxide corrections were necessary. Calibration was performed using multi-element solutions freshly prepared from commercial ICP-MS standards certified to better than 1% uncertainty and verified by multiple repeats of the CAL-S reference material that were included as unknowns in every session. Values for PAAS normalisation are from ref. 60.

## La-Ce isotope analysis

For samples selected for La-Ce isotope analyses, larger quantities (between 0.53 and 14 g) of powder were digested overnight at room temperature in variable quantities of 5% trace-metal-grade acetic acid, and small aliquots were dried at 90° C, taken up and dried down three times in concentrated HNO₃ to remove any traces of acetic acid, and analysed by HR-ICP-MS using methods similar to above. For these sessions, potential matrix effects were monitored and excluded using multi-element standards variably doped in Ca. ¹³⁸La/¹⁴²Ce ratios were determined by normalisation of the blank-subtracted La/Ce signal to that of the in-house reference material BEAN⁶¹, with the CAL-S reference material (CRPG Nancy) employed as a validation standard. As there exist significant uncertainties in the ¹³⁸La/¹⁴²Ce ratios of available carbonate reference materials⁶¹, for this work we independently determined the ¹³⁸La/¹⁴²Ce ratios of BEAN and CAL-S using isotope dilution multi-collector ICP-MS (ID-MC-ICP-MS; see Supplementary Table 4). Briefly, aliquots of each reference material were spiked
individually with separate, gravimetrically prepared <sup>139</sup>La and <sup>142</sup>Ce tracer solutions in duplicate, digested in acetic acid as above, La and Ce were separated using TODGA resin as per ref. 61, and purified cuts analysed using a ThermoFisher Neptune MC-ICP-MS in low resolution mode with the addition of Nd and Sm (for La and Ce, respectively) for mass bias correction using <sup>146</sup>Nd/<sup>142</sup>Nd = 0.63304239 and <sup>149</sup>Sm/<sup>147</sup>Sm = 0.92135431 (values from ref. 62). Duplicate ID-MC-ICP-MS analyses of the reference material BHVO-2 digested in concentrated HF-HNO<sub>3</sub>-HCl and purified as described above yielded an La/Ce ratio of 0.401 ± 0.007 g/g, identical within uncertainty to other available ID-MC-ICP-MS data<sup>63,64</sup>. Uncertainties on <sup>138</sup>La/<sup>142</sup>Ce ratios were propagated from uncertainties on the composition of the normalising reference material (BEAN), the random uncertainty determined by repeat analyses of the normalising reference material, and the excess uncertainty in the values obtained for the validation material (CAL-S) across all sessions relative to its ID-MC-ICP-MS value (see Supplementary Table 4), following the general schema outlined in ref. 65 (see Supplementary Information).

For <sup>138</sup>Ce/<sup>142</sup>Ce analysis, cerium was purified using a four-column procedure modified from ref. 54. First, major elements were removed using 1 ml of TRU resin (50-100 µm) in 10 mL Bio-Rad columns. Major elements were eluted in 1 M HNO<sub>3</sub> and REE were then eluted in 0.05 M HNO<sub>3</sub> and 0.1 M HCl + 0.29 M HF. Samples were then loaded onto 2 mL of AGW50-X8 resin (200-400 µm) in 10 mL Bio-Rad columns and the remaining major elements were eluted in 2.5 M HCl, then Ba eluted in 2 M HNO<sub>3</sub>, and REE were finally eluted in 6 M HCl. Cerium was then isolated from other REE as Ce(IV) using 0.4 ml of Ln-Spec resin (50-100 µm) in 2 ml Bio-Rad columns with oxidation and loading in 20 mM NaBrO<sub>3</sub> dissolved in 10M HNO<sub>3</sub>, followed by elution in 6M HCl. Finally, Na introduced in the previous step as well as any remaining Ba was removed from the purified Ce cuts by loading of the sample in 2M HCl onto AGW50-X8 resin (200-400 µm) followed by elution in 6M HCl. All Ce isotope analyses were performed on a ThermoFisher Triton Plus TIMS at the Laboratoire Magmas et Volcans (LMV) in Clermont-Ferrand, France. Samples were loaded onto degassed double Re filaments with H<sub>3</sub>PO<sub>4</sub> activator and analysed in oxide form using the protocols and cup configurations detailed in ref. 54. Data were acquired for 540 cycles with 8.4 s integration times and 2σ outliers were rejected. Intensities ranged from 0.06 V to 0.25 V on <sup>138</sup>Ce<sup>16</sup>O with a mean of 0.15 V, and 2.6 V to 11.3 V for <sup>142</sup>Ce<sup>16</sup>O with a mean of 6.64 V. External uncertainty on <sup>138</sup>Ce/<sup>142</sup>Ce ratios was constrained by repeat analyses of the Ce isotope standard Ce-LMV across all TIMS analytical sessions (mean = 0.02256983, 2s = 0.000000477, or 21.1 ppm; n=11; Supplementary Table 5).
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The $\varepsilon^{138}\text{Ce}_{\text{initial}}$ values presented in the main text were calculated with respect to CHUR, corrected for the stated U-Pb depositional ages for each site, using the modern CHUR La/Ce and $^{138}\text{Ce}/^{142}\text{Ce}$ values of 0.387 ± 0.022 and 0.02256577 ± 66 (respectively; 2s errors)$^{66}$. All $^{138}\text{La}/^{138}\text{Ce}$ values were calculated as La/Ce * 0.00804772, as per ref. 67, yielding a modern CHUR $^{138}\text{La}/^{138}\text{Ce}$ value of 0.00311447 ± 0.00017705 (2s). Isochrons were calculated with the York regression model (model 1) of Isoplot R$^{68}$ using updated estimates$^{53}$ of the $^{138}\text{La}$ half-life and decay branching ratios; see ref. 69 for a detailed discussion of these estimates and their uncertainties. These values yield decay constants of 2.328 x 10$^{-12}$ yr$^{-1}$ for $^{138}\text{La}$ $\beta^-$ decay to $^{138}\text{Ce}$ and 4.362 x 10$^{-12}$ yr$^{-1}$ for $^{138}\text{La}$ $\beta^+$ decay to $^{138}\text{Ba}$; the reported La-Ce ages consider both branches. All uncertainties are 2s unless specified otherwise.

## Estimation of uncertainties and statistical support

Methods detailing the estimation of uncertainty as well as a discussion on statistical support for the reported La-Ce closure ages are provided in the Supplementary Information.
542

References cited only in the online methods section and supplementary information

543

544

58. Rongemaille, E. et al. Rare earth elements in cold seep carbonates from the Niger delta.

545

*Chem Geol* **286**, 196–206 (2011).

546

547

59. Cao, C., Liu, X.-M., Bataille, C. P. & Liu, C. What do Ce anomalies in marine carbonates

548

really mean? A perspective from leaching experiments. *Chem Geol* **532**, 119413 (2020).

549

60. Taylor, S. R. & McLennan, Scott. M. *The continental crust: its composition and evolution;*

550

*an examination of the geochemical record preserved in sedimentary rocks*. (Blackwell,

551

1985).

552

61. Barrat, J.-A. et al. A new chemical separation procedure for the determination of rare earth

553

elements and yttrium abundances in carbonates by ICP-MS. *Tantala* **219**, 121244.

554

555

62. Meija, J., et al. Isotopic compositions of the elements 2013 (IUPAC Technical Report).

556

*Pure Appl. Chem.* **88**, 293–306 (2016)

557

558

63. Kent, A.J.R. et al. Isotope Dilution MC-ICP-MS Rare Earth Element Analysis of

559

Geochemical Reference Materials NIST SRM 610, NIST SRM 612, NIST SRM 614,

560

BHVO-2G, BHVO-2, BCR-2G, JB-2, WS-E, W-2, AGV-1 and AGV-2. *Geostand*

561

*Geoanal Res* 28, 417–429 (2004).

562

563

64. Schnabel, C, Münker, C., and Strub, E. La-Ce isotope measurements by multicollector-

564

ICPMS. *J. Anal. At. Spectrom.*, DOI: 10.1039/c7ja00256d (2017).

565

566

65. Horstwood et al. Community-derived standards for LA-ICP-MS U-(Th)-Pb

567

geochronology – uncertainty propagation, age interpretation, and data reporting.

568

*Geostand. Geoanal. Res.* **40**, 311–332 (2016).

569

570

66. Israel, C. et al. Formation of the Ce-Nd mantle array: Crustal extraction vs. recycling by

571

subduction. *Earth Planet Sc Lett* **530**, 115941 (2020).

572

573

67. Israel, C. Retracer l'évolution de la Terre silicatée par le couplage des systèmes lanthane-

574

cérium et samarium-néodyme. Doctoral thesis, Université Clermont-Auverge (2021).

575

Retrieved from https://theses.hal.science/tel-03563967.

576

577

68. Vermeesch, P. IsoplotR: A free and open toolbox for geochronology. *Geosci Front* **9**, 1479–

578

1493 (2018).

579

580

69. Mougeot, X. & M.-M., Bé. ¹³⁸La - comments on evaluation of decay data. In Bé, M.-M. et

581

al., Table of Radionuclides (Comments on evaluation). (Bureau International des poids et

582

mésures, Monographie BIPM-5, 2016).

583

584

70. Brooks, C., Hart, S.R., and Wendt, I. Realistic Use of Two-Error Regression Treatments as

585

applied to Rubidium-Strontium data. *Reviews of Geophysics and Space Physics* **10**, 551–

586

577 (1972).

587

588
589 Acknowledgements

590 This work was supported by the European Research Council (ERC) under the European
591 Union's Horizon 2020 research and innovation programme (grant agreement n° 716515 to
592 S.V.L. and grant agreement n° 682778 to M.B.). The authors thank the owners and staff of the
593 Bow Narrows and Woman River Camps for their hosting and logistical support, Sophie
594 Kurucz, Sean Timpa, and Robert Riding for their assistance in the field, Nicolas Richet, Yoann
595 Lallaizon and Jean-Pierre Oldra for their assistance with sample preparation, Jean-Alix Barrat,
596 Marie-Laure Rouget, Céline Liorzou, Bleuenn Gueguen, and Delphine Auclair for their
597 analytical support, the administrative staff of the Geo-Ocean Laboratory and Lakehead
598 University for their organizational support, and Jean-Alix Barrat, Michael Bau, and Kurt
599 Konhauser for stimulating discussions regarding this work.

600

601 Author Contributions

602 S.V.L. designed the research with contributions from P.B. and P.W.F. Fieldwork and sample
603 collection were performed by P.W.F., M.A., B.R., D.T.W., S.V.L., M.H., P.S., and L.A.P.
604 under the supervision of P.W.F. and S.V.L., and M.A., D.T.W., B.R., L.A.P., M.H., and S.V.L.
605 generated the REE datasets. L.A.P. prepared and conducted the La-Ce isotope analyses with
606 the assistance of P.B., P.N., and M.B. Data analysis was performed by L.A.P., P.B., S.V.L.,
607 M.B., M.A., D.T.W., and B.R., and L.A.P., P.B., and S.V.L. wrote the manuscript with
608 contributions from all co-authors.

609

610 Corresponding authors

611 Correspondence to Pierre Bonnand and Stefan V. Lalonde.

612

613 Competing interests

614 The authors declare no competing interests.

615

616
<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

Extended Data Figure 1. La-Ce isotope data evaluated with respect to theoretical evolution from CHUR and as a function of Ce concentrations (a) <sup>138</sup>La-<sup>138</sup>Ce isotope systematics of the combined dataset from the three studied Archean carbonate platforms, superimposed on the theoretical <sup>138</sup>La-<sup>138</sup>Ce evolution trajectories drawn for 0.1 Ga, 1 Ga, 2 Ga, and 3 Ga from a CHUR-like initial precursor. For clarity, data points are enlarged relative to the measured analytical uncertainties. (b) Plots of measured Ce isotope compositions and (c) initial Ce isotope composition versus 1/Ce concentrations (in ppm) reveal no systematic correlations that might indicate that the reported isochrons are the result of disturbance or mixing of different Ce sources.
<figure><img src="image_13.png" /><figcaption>b</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>c</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>d</figcaption></figure>

<figure><img src="image_16.png" /></figure>

**Extended Data Figure 2. Probability distributions of La-Ce closure ages.** La-Ce closure age probabilities for (a) the isochron fits as reported in the main text, (b) the same isochron fits for which ages are calculated using the upper 2s uncertainty limits of the ¹³⁸La decay constants (see Methods), (c) isochron fits obtained if a student t-test expansion is applied to the analytical uncertainty determined in our study for the ¹³⁸La/¹³⁸Ce ratios, and (d) isochron fits for the case where 2s uncertainties on the ¹³⁸La/¹³⁸Ce ratios are expanded artificially from 3.85% to 10% (see Supplementary Information). For (d), the joint probability of all three La-Ce closure ages versus time (dotted line) is provided on the second y-axis, demonstrating that even if analytical uncertainties were underestimated in this study, the joint probability that all three La-Ce isochrons may represent oxidation that occurred during the GOE is effectively excluded. The minimum depositional ages for each site as determined by zircon U-Pb geochronology are presented as vertical bars, with the width of each bar representing the 2s uncertainty; in the case of Steep Rock, the uncertainty on the U-Pb minimum depositional age has been artificially expanded by a factor of 4 for visibility. See Supplementary Information for additional details.