Here's a Bubble That's Ready to Burst: Oxygen as an Explanation for the Cambrian Explosion - Evolution News & Views

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Here's a Bubble That's Ready to Burst: Oxygen as an Explanation for the Cambrian Explosion

oxygen bubbles.jpg

It's surely a sign of desperation when Darwinists have nothing more in their toolkit than oxygen to build complex body plans. All these new phyla, they think, really wanted to evolve. They just couldn't until all the microbes in the oceans brought the oxygen level up to regulations.

Take, for example, a group of Australian science reporters under the umbrella Science in Public. Their website lists as their goals, "We believe science should be: • Brought out of the lab, • Conducted in public, • Debated in public, • Criticised in public." So how did they do when discussing the Cambrian explosion, a huge problem for Darwinian evolution brought to public attention by Stephen Meyer's bestselling book, Darwin's Doubt? The headline is the tip-off: "Life stuck in slime for a billion years." The culprit: oxygen.

The first life developed in the ancient oceans around 3.6 billion years ago, but then nothing much happened. Life remained as little more than a layer of slime for a billion years. Suddenly, 550 million years ago, evolution burst back into action -- and here we are today. So what was the hold-up during those 'boring billion' years?

According to University of Tasmania geologist Professor Ross Large and his international team, the key was a lack of oxygen and nutrient elements, which placed evolution in a precarious position. "During that billion years, oxygen levels declined and the oceans were losing the ingredients needed for life to develop into more complex organisms." (Emphasis added.)

Since they believe science should be debated in public and criticized in public, we can expect the article to present some honest debate and criticism of this notion, shouldn't we? Crickets.

The article informs us that the international team was "able to show that the slowdown in evolution was tightly linked to low levels of oxygen and biologically important elements in the oceans." It's been shown. It's science; there's nothing more to debate.

After an initial burst of oxygen, the study plots a long decline in oxygen levels during the 'boring billion' years before leaping up about 750-550 million years ago. "We think this recovery of oxygen levels led to a significant increase in trace metals in the ocean and triggered the 'Cambrian explosion of life'.

We've discussed this notion before here and here. Just add oxygen, and voila! Animals! While it's true that fire needs oxygen, one usually doesn't find two dozen complex body plans emerging from explosions. Yet, crazy as it is, it keeps coming up. Most of the major journals have repeated it.

Science Magazine chimed in with a book review of Oxygen: A Four Billion Year History by Donald E. Canfield. Once again, reviewer Woodward W. Fischer makes oxygen the hero of the rise of Cambrian animals:

If one could boil all of Earth's behavior down to a single number -- a statistic that captured the rich intersection of geological, chemical, and biological processes operating on our planet's surface -- a strong argument could be made for the atmosphere's O2 content. That is presently 21% by volume, but a wide range of data extracted from the geologic record demonstrates that O2 levels have varied considerably. To first order, Earth's history is written in O2, and tangled in the story are plate tectonics, the rock cycle, the evolution of photosynthesis, and the appearance of animals.

Nature calls it a compelling story:

The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth's history.

Although the paper's main text doesn't mention the Cambrian explosion, there's no doubt the authors' purpose was to try to explain it, because "Cambrian" and "Precambrian" are mentioned in ten of the references. One of them refers to a 2011 Science paper, "The Cambrian Conundrum," co-authored by Smithsonian paleobiologist Douglas Erwin. The authors add this annotation in bold text:

Essential overview of our present understanding of the cause-and-effect relationships among early animal evolution and diversification, increasing ecological complexity, and environmental change -- particularly oxygenation of the ocean and atmosphere.

DebatingDDsmall.jpegSo they do a lateral pass to Erwin and others.

Besides, one doesn't have to mention "Cambrian explosion" outright to suggest it indirectly with lines like, "overall low oxygen availability, challenge the emergence and diversification of eukaryotic organisms and animals until the final big step in the history of oxygenation and the expansion of life." (Emphasis added.) Low oxygen, we are told, "throttled the early diversity, distribution and abundances of eukaryotes." You see, the animals were offstage gasping for breath, eager to make their appearance.

With that reference to Erwin's and another paper about oxygen leading to the Cambrian explosion, Nature continues the theme:

Others [sic] researchers assert various scenarios that demand oxygen in appreciable amounts to explain high animal diversity, large mobile bilaterians, the advent of biomineralization (skeletons), wide niche expansion including habitats below the sea floor, and complex predator-prey relationships.

Nowhere will you find intelligent design offered "to explain high animal diversity" seen in the fossil record. It wasn't design holding the animals back; it was low oxygen maintaining a "strangle-hold on early complex life." It sounds like we're watching a wrestling match, with Low-oxygen keeping Evolution in a chokehold. Until Evolution breaks free, his hands are tied.

This imaginary drama goes on, we know, because only "geobiological" causes are allowed:

Finally, researchers will ask more and better questions about the unique confluence of global-scale climatic, evolutionary and tectonic events that once and for all broke the cycle of low oxygen on Earth, less than a billion years ago, and set the stage for everything that followed, including the emergence of animal life.

No wonder the animals couldn't emerge. No one could "set the stage" for them until oxygen was pumped into the theater.

Nature pins most of its support for this notion on the so-called "Great Oxygenation Event" (GOE) that supposedly occurred prior to the Ediacaran period preceding the Cambrian. They admit, though, that this GOE now appears to have been more of a lengthy transition (GOT) than an event. Like tea leaves, rocks can be read different ways.

As David Klinghoffer has pointed out here already, PNAS just threw a monkey wrench into the oxygen hypothesis. A new paper undermines the idea that low oxygen restricted the emergence of complex life. Daniel Mills, a graduate student from the University of Southern Denmark, showed in the lab that sponges can survive just fine under low oxygen conditions.

We provide experimental evidence suggesting that the last common ancestor of animals could have thrived in oxygen levels as low as 0.5% to 4% of present atmospheric levels, which were likely met on Earth well before animals evolved. This was achieved by observing the survival of sponges, basal animals similar to the earliest metazoans, under low-oxygen conditions in the laboratory. These results encourage us to reconsider the environmental constraints on the origin of animal life.

What Mills and colleagues are saying is that oxygen is no excuse. Complex animal life could have evolved much earlier. A news release from his university states that the low oxygen levels in the lab are "lower than the oxygen levels we thought were necessary for animal life." In fact, earlier work had already done more damage to the oxygen theory:

His colleagues from the Nordic Center for Earth Evolution have previously shown that oxygen levels have actually risen dramatically at least one time before complex life evolved. Although plenty of oxygen thus became available it did not lead to the development of complex life.

This pulls the rug out from the oxygen theory. What is Mills going to replace it with? He tells us:

"There must have been other ecological and evolutionary mechanisms at play. Maybe life remained microbial for so long because it took a while to develop the biological machinery required to construct an animal. Perhaps the ancient Earth lacked animals because complex, many-celled bodies are simply hard to evolve", says Daniel Mills.

In other words, for Darwinians, it's back to square one.

Image: Oxygen bubbles, Ben Adams/Flickr.


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