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Scientists: Oxygen “Fueled” Evolution of Complex Life


Writing at the tail end of Cenozoic Era, Dante wouldn’t have progressed very far in composing his poetry if the oxygen content of the late medieval Italian atmosphere were too low to sustain life. Oxygen was a condition for his work. However, nobody would say that it “fueled” Dante’s creativity. Maybe his love for Beatrice did.

Yet over at Science Daily we find another retelling of the oxygen theory of the Cambrian explosion, with the vital gas as the “fuel” for evolution’s creativity (“Oxygen levels were key to early animal evolution, strongest evidence now shows“).

It has long puzzled scientists why, after 3 billion years of nothing more complex than algae, complex animals suddenly started to appear on Earth. Now, a team of researchers has put forward some of the strongest evidence yet to support the hypothesis that high levels of oxygen in the oceans were crucial for the emergence of skeletal animals 550 million years ago.

The new study is the first to distinguish between bodies of water with low and high levels of oxygen. It shows that poorly oxygenated waters did not support the complex life that evolved immediately prior to the Cambrian period, suggesting the presence of oxygen was a key factor in the appearance of these animals.

No oxygen, no animal life. Therefore “poorly oxygenated waters” would seem to be an undoubted “factor in the appearance of [complex] animals,” meaning a necessary but certainly not sufficient condition.

The study appears in Nature Communications. Its lead author, Rosalie Tastevin at Oxford University, says:

The question of why it took so long for complex animal life to appear on Earth has puzzled scientists for a long time. One argument has been that evolution simply doesn’t happen very quickly, but another popular hypothesis suggests that a rise in the level of oxygen in the oceans gave simple life-forms the fuel they needed to evolve skeletons, mobility and other typical features of modern animals.

Although there is geochemical evidence for a rise in oxygen in the oceans around the time of the appearance of more complex animals, it has been really difficult to prove a causal link. By teasing apart waters with high and low levels of oxygen, and demonstrating that early skeletal animals were restricted to well-oxygenated waters, we have provided strong evidence that the availability of oxygen was a key requirement for the development of these animals. [Emphasis added.]

Who would doubt it? In fact the study’s title, “Low-oxygen waters limited habitable space for early animals,” sounds about as uncontroversial as it could. Naturally, a lack of oxygen limits “habitable space.” But note the apparent confirmation of the “popular hypothesis” that oxygen, that popular gas, was the “fuel” for evolving “skeletons, mobility and other typical features of modern animals.”

The Abstract is clearer:

The oceans at the start of the Neoproterozoic Era (1,000-541 million years ago, Ma) were dominantly anoxic, but may have become progressively oxygenated, coincident with the rise of animal life. However, the control that oxygen exerted on the development of early animal ecosystems remains unclear, as previous research has focussed on the identification of fully anoxic or oxic conditions, rather than intermediate redox levels. Here we report anomalous cerium enrichments preserved in carbonate rocks across bathymetric basin transects from nine localities of the Nama Group, Namibia (∼550-541 Ma). In combination with Fe-based redox proxies, these data suggest that low-oxygen conditions occurred in a narrow zone between well-oxygenated surface waters and fully anoxic deep waters. Although abundant in well-oxygenated environments, early skeletal animals did not occupy oxygen impoverished regions of the shelf, demonstrating that oxygen availability (probably >10 μM) was a key requirement for the development of early animal-based ecosystems.

Oxygen is the currently favored explanation for the abrupt appearance of animal life, but Evolution News commented recently that it’s a nonstarter. “Coincident,” sure, a “requirement,” fine, but not “fuel”:

The goal of science is to provide a vera causa for observed effects. Except in some highly imaginative fiction, oxygen is not a creative evolutionary force. A gas cannot devise body plans. A living archaeal cell at a deep sea vent is not the ancestor to all eukaryotes. Complex specified information is present. Molecular machinery is present. What necessary and sufficient cause other than intelligence can explain these observed realities?

What “fuels” evolution — whether purpose, as Stephen Meyer and other ID advocates argue, or blind churning — is precisely the question at stake in the Darwin debate. Researchers seeking to explain away the Cambrian event without intelligent design are left with a tough choice. What they can say that’s true is unremarkable. What they say that is false, or misleading, is also obviously absurd.

Photo: Rosalie Tostevin in Namibia, by Fred Bowyer via Science Daily.