This Fossil Friday features the weird critter Hallucigenia from the Cambrian Burgess Shale, as we discuss the most recent contribution to the Cambrian Explosion bingo game, which is how I prefer to call the popular exercise in wild speculation and unsubstantiated guesswork among evolutionary biologists to explain the abrupt appearance of animal body plans in the Cambrian Explosion about 535-515 million years ago. Among the many different causes that have been proposed as alleged drivers of the Cambrian Explosion, an increase in oxygen levels represents one of the most popular alternatives (e.g., see Zhang & Cui 2016, He et al. 2019). It was claimed that “oxygen linked with the boom and bust of early animal evolution” (University of Oxford 2019). Even as recently as two years ago, scientists found that there were “pulses of atmosphere oxygenation during the Cambrian radiation of animals” and “oxygen availability was a crucial factor in accelerating the radiation of marine animals” (Jiang et al. 2022).

This Just In

Now, a new study by Stockey et el (2024), just published in the journal Nature Geoscience, did not “find evidence for the wholesale oxygenation of Earth’s oceans in the late Neoproterozoic era”, but instead just a “moderate long-term increase”. The authors suggest that this small increase “provides some of the most direct evidence for potential physiological drivers of the Cambrian radiation.” Consequently the press releases and media headlines cheered that scientists found that “a rapid burst of evolution 540 million years ago could have been caused by a small increase in oxygen” (Castañón 2024), and a “small change in Earth’s oxygen levels may have sparked huge evolutionary leap” (University of Southampton 2024), and “life only needed a small amount of oxygen to explode” (Watson 2024). This is quite surprising, as the latter author explicitly admitted that “it’s long been thought that a monumental surge in oxygen fuelled the Cambrian explosion” (Watson 2024). However, suddenly it allegedly was not a monumental surge but just a small long-term increase that made this miracle happen. Hey, no big deal, they just creatively changed the narrative.

Who Cares About Yesterday’s Petty News?

I bet that if scientists were to discover next month that there was no oxygenation in the Cambrian but the exact opposite, they would quickly reverse their just-so-story and claim that it was lower oxygen levels that caused the Cambrian Explosion. If you doubt that distinguished scientists could or would ever be that sloppy and cunning, just look what they did with the event that preceded the Cambrian Explosion in the Ediacaran. Spoiler alert: they did exactly that, which I already discussed at length in a previous article (Bechly 2023a) and podcast (Bechly 2023b). Check it out if you want to dig deeper down this rabbit hole.

References

• Bechly G 2023a. Fossil Friday: Seventy Years of Textbook Wisdom on Origin of Multicellular Life Turns Out to Be Wrong. Evolution News September 1, 2023. https://evolutionnews.org/2023/09/fossil-friday-seventy-years-of-textbook-wisdom-on-the-origin-of-multicellular-life-turns-out-to-be-wrong/
• Bechly G 2023b. Günter Bechly on Why Seventy Years of Textbook Wisdom Was Wrong. ID the Future episode 1813. https://idthefuture.com/1813/
• Castañón L 2024. Revisiting the Cambrian explosion’s spark. Stanford Report July 2, 2024. https://news.stanford.edu/stories/2024/07/revisiting-the-cambrian-explosion-s-spark
• He T, Zhu M, Mills BJW et al. 2019. Possible links between extreme oxygen perturbations and the Cambrian radiation of animals. Nature Geoscience 12, 468–474. DOI: https://doi.org/10.1038/s41561-019-0357-z
• Jiang L, Zhao M, Shen A, Huang L, Chen D & Cai C 2022. Pulses of atmosphere oxygenation during the Cambrian radiation of animals. Earth and Planetary Science Letters 590: 117565. DOI: https://doi.org/10.1016/j.epsl.2022.117565
• Stockey RG, Cole DB, Farrell UC et al. 2024, Sustained increases in atmospheric oxygen and marine productivity in the Neoproterozoic and Palaeozoic eras. Nature Geoscience. DOI: https://doi.org/10.1038/s41561-024-01479-1
• University of Oxford 2019. Oxygen linked with the boom and bust of early animal evolution. University of Oxford News & Events May 13, 2019. https://www.ox.ac.uk/news/2019-05-13-oxygen-linked-boom-and-bust-early-animal-evolution
• University of Southampton 2024. Small change in Earth’s oxygen levels may have sparked huge evolutionary leap. Phys.org July 2, 2024. https://phys.org/news/2024-07-small-earth-oxygen-huge-evolutionary.html
• Watson C 2024. Life Only Needed A Small Amount of Oxygen to Explode, Scientists Find. ScienceAlert July 7, 2024. https://www.sciencealert.com/life-only-needed-a-small-amount-of-oxygen-to-explode-scientists-find
• Zhang X & Cui L 2016. Oxygen Requirements for the Cambrian Explosion. Journal of Earth Science 27(2), 187–195. DOI: https://doi.org/10.1007/s12583-016-0690-8