Cambrian Explosion: Sedimentary, My Dear Flotsam
“Then something happened.” Question: are you reading a science article, or a fictional screenplay? Are you in the Science Department or the Humanities Department? Are you in the lab or the theater? Find out in today’s episode of “Explain the Cambrian Explosion.”
The short sentence “Then something happened” appears in a press release from the University of Wisconsin-Madison, entitled, “Great Unconformity: Evidence for a geologic trigger of the Cambrian explosion” (see it also on PhysOrg). The references to geology, fossils and evidence sure sounds like this is coming from the science lab. Here’s the context:
The oceans teemed with life 600 million years ago, but the simple, soft-bodied creatures would have been hardly recognizable as the ancestors of nearly all animals on Earth today.
Then something happened. Over several tens of millions of years – a relative blink of an eye in geologic terms – a burst of evolution led to a flurry of diversification and increasing complexity, including the expansion of multicellular organisms and the appearance of the first shells and skeletons.
The results of this Cambrian explosion are well documented in the fossil record, but its cause – why and when it happened, and perhaps why nothing similar has happened since – has been a mystery.
The conflict having been set up, it’s time for the protagonist to enter the stage:
New research shows that the answer may lie in a second geological curiosity – a dramatic boundary, known as the Great Unconformity, between ancient igneous and metamorphic rocks and younger sediments.
The new research, naturally, comes from the sponsors of the play, the University of Wisconsin public relations department, eager to promote their scientific star, Shanan E. Peters (his buddy, Robert R. Gaines, is from Pomona College in California). To save time, let’s bypass the commercial and go to the actual research published in Nature this week (Nature 484, 19 April 2012, pp. 363–366; doi:10.1038/nature10969) to see what Shanan & Robert have to show & tell. Will it take us from the humanities theater back to the science lab? Will they be able to use that “second geological curiosity” to solve the first “mystery”? Will it “hold the key to understanding what happened” as Shanan promised in the press release? Or will it be just entertainment?
The paper sure looks scientific. It’s loaded with graphs, charts, data, references, and the general layout of a scientific report. Nature even made it their cover story, complete with a beautiful shot of the Grand Canyon and a bold title, “LIFE FORCE: Did the Formation of the Great Unconformity trigger the Cambrian Explosion?” What needs to be determined is whether these are stage props or the real thing. It’s not enough to have props, we all know. The data have to actually apply to a hypothesis, which, in turn, needs to explain the data better than any other competing hypothesis. Since the subject matter involves the unobservable past, science can only infer to the best explanation. That means competing explanations have to be listed and evaluated on their merits. (It’s also nice to avoid backpedaling from the previous best explanation, even though logically, retreating from a wrong explanation is technically a kind of “progress.”)
The first thing we notice is that Drs. Peters and Gaines have limited themselves to Darwinian explanations, and have assumed the geological timescale with all its embedded Darwinian assumptions. This convenient move simplifies the playing field considerably. Not only can they dismiss intelligent design (which they undoubtedly dismiss as unscientific from the get-go anyway), but also every other non-Darwinian explanation for the Cambrian explosion. Then we notice them utilizing “gaps” as “data.” Their last sentence sums up their hypothesis nicely:
Although Darwin and other palaeontologists [sic; Darwin’s only degree was in theology] have regarded the resultant widespread hiatus in the rock record as a failure of preservation, the formation of this prominent gap may have actually been an environmental trigger for biomineralization, thereby promoting the Cambrian explosion of marine animals. Determining the geodynamic causes of extensive Neoproterozoic continental denudation followed by Phanerozoic sedimentation, and linking those dynamics to the timing and spatial distribution of marine transgression and biogeochemical change, is now a challenge for geoscience.
So not only have Peters & Gaines pulled a rabbit out of a gap (whether Precambrian or Cenozoic rabbit is not at issue here), they have promised a sequel. The sequel is to fill in the scientific explanation for the scenario they just imagined. This remarkable paragraph states clearly that (1) the gap only “may have” been an “environmental trigger” for the Cambrian explosion, (2) they have not identified a geodynamic cause for their imaginary denudation of the continents down to basement rock, (3) they have not provided a cause for subsequent sedimentation (complete with complex Cambrian animals fully formed within them), and (4), they have not been able to link the imaginary geological processes to the imaginary biogeochemical changes that brought trilobites out of new seawater chemistry. That’s somebody else’s job– “a challenge for geoscience.”
Now we can understand the press release where Peters wraps up the scenario with a storybook ending:
“The French composer Claude Debussy said, ‘Music is the space between the notes.‘ I think that is the case here,” he says. “The gaps can have more information, in some ways, about the processes driving Earth system change, than the rocks do. It’s both together that give the whole picture.”
Clap if your scientific understanding has increased.
It was really hard to be charitable to these guys without cracking up. Sometimes it’s just impossible. Here’s what you just learned. The Great Unconformity, “occurring worldwide,” a profound “mystery” to geologists who wonder why a billion Darwin years passed before sediments were deposited on its global, pancake-flat surface, known to Charles Darwin to represent “a huge gap in the rock record and in our understanding of the Earth’s history,” is not the problem. The gap is the solution. We can use the contents of the hole to fill another hole – the abrupt appearance of all the animal body plans in “a relative blink of an eye in geologic terms” – the Cambrian explosion. We can take the space between the notes in Debussy (i.e., the silence) to fill the silence in Ravel. In the limit (since intelligent design is ruled out, whether from Debussy or Paley) we end up with John Cage, 4 minutes and 33 seconds of pure silence. Science marches on!
Let’s give charity one more chance. Didn’t the magician team of Peters & Gaines present a hypothesis? Didn’t they say that during that gap, something happened? Or course they did. Stuff happens in Darwinland.
During the early Cambrian, shallow seas repeatedly advanced and retreated across the North American continent, gradually eroding away surface rock to uncover fresh basement rock from within the crust. Exposed to the surface environment for the first time, those crustal rocks reacted with air and water in a chemical weathering process that released ions such as calcium, iron, potassium, and silica into the oceans, changing the seawater chemistry.
Now, isn’t that a scientific hypothesis that takes us from the theater to the lab? No. This is all part of the gap. They filled the gap with their own imaginations. There’s no evidence that shallow seas repeatedly advanced and retreated, wearing down imaginary sediments to basement rock all over the world. There’s only the gap– igneous basement rock, with flat sediments stacked on top of them a billion Darwin Years later. This is clearly visible in the Grand Canyon, but it represents a global phenomenon. That’s why it’s called the Great Unconformity. Furthermore, there’s only one Great Unconformity, so they have not found a Law of Nature that creates global unconformities from time to time. Peters himself said in the press release, “there’s nothing else like it in the entire rock record.”
To avoid the predictable mud and riots, we don’t dare mention some non-Darwinian scientists who use the Great Unconformity and the Cambrian Explosion as evidence against Darwinism.
But we don’t have to. We can use Peters & Gaines themselves, and their whole support network (Nature, PhysOrg, and the University of Wisconsin-Madison) to evaluate the credibility of their idea. During an imaginary billion-year gap that left no sign of gully erosion on a global flat surface while imaginary seas advanced and retreated. “Then something happened.” New minerals changed the chemistry of seawater. This “triggered” a geologically-sudden explosion of complex body plans with eyes, articulated limbs, digestive systems, muscles and nerves. In science, it’s now permissible to use gaps to fill gaps. You can use silence to fill silence. You can use imagination in lieu of scientific data. Stuff happens: in modern Darwinian thinking, that’s all you need to know. Imagining what may happen in the gaps gives you Understanding – Enlightenment – Nirvana.
Predictably, NASA’s Astrobiology Magazine regurgitated this fact-free press release without analysis or criticism, except for dressing it up with irrelevant artwork and photos that having nothing to do with the imaginary scenario Peters & Gaines proposed. At the end it stated that the work (if it can be called that) was funded by the National Science Foundation. Your tax dollars at work (like at the GSA).
Experiment: Pour powdered igneous rock into a tank of seawater with microbes in it. Isolate. Wait a billion years and observe what happens. A half-sheet of paper should be sufficient for note taking. To bide the time, imagine wondrous things: pigs with wings, cabbages and kings.