Wintery Knight

…integrating Christian faith and knowledge in the public square

How brief was the period in which the Cambrian phyla suddenly appeared?

The Cambrian explosion refers to the sudden appearance of new body plans in the fossil record. ID proponents think that the period is between 5-10 million years at the most. Naturalists want to stretch out the period in which the body plans appear to tens of millions of years. The two sides can’t both be right. What’s the truth?

Evolution News has the answer.

Excerpt:

To establish the length of the most explosive period of innovation within the Cambrian explosion itself, Meyer cites the work of MIT geochronologist Samuel Bowring and his colleagues as well the work of another group led by Smithsonian paleontologist Douglas Erwin. The Bowring-led study showed that (in their words) “the main period of exponential diversification” within the Cambrian lasted “only 5-6 million years” (emphasis added). Meyer explains:

An analysis by MIT geochronologist Samuel Bowring has shown that the main pulse of Cambrian morphological innovation occurred in a sedimentary sequence spanning no more than 6 million years. Yet during this time representatives of at least sixteen completely novel phyla and about thirty classes first appeared in the rock record. In a more recent paper using a slightly different dating scheme, Douglas Erwin and colleagues similarly show that thirteen new phyla appear in a roughly 6-million-year window. (p. 73)

[...][T]ake a look first at the following figure that Bowring and his colleagues included in their definitive 1993 article, published in the journal Science. They use radiometric methods to date the different stages of the Cambrian period, including the crucial Tommotian and Atdabanian stages in which the greatest number of new animal phyla and classes arise. Note that the so-called Manykaian stage of the Cambrian period lasts about 10-14 million years. Note also that the main pulse of morphological innovation didn’t begin during this stage but rather during the Tommotian and Atdabanian — a period that they describe as taking between “5 to 10 million years,” and in a more detailed passage as taking about 5-6 million years.

[...]In the figure above, the Tommotian and Atdabanian stages of the Cambrian period together span only about 5 million years, starting at about 530 and ending about 525 million years ago. Bowring’s figure also depicts the total number of classes and orders present at any given time during the Cambrian period. The biggest increases in morphological innovation occur during the Tommotian and Atdabanian stages. Indeed, during this period the number of known orders nearly quadruples. Moreover, Bowring and his colleagues also make clear that this period corresponds to the main pulse of Cambrian morphological innovation as measured by the number of new phyla and classes that first appear. They note that, while a few groups of animals do arise in the earliest Manykaian stage of the Cambrian, the most rapid period of “exponential increase of diversification,” corresponding to the Tommotian and Atdabanian stages, “lasted only 5 to 6 m.y.”

You can see the figure they are reference in the Evolution News article.

Also, check out these clips that explain the Cambrian explosion:

Part 1:

Part 2:

The first clip features James Valentine, a professor of biology at the University of California who just co-authored a new book on the Cambrian explosion and is not a proponent of intelligent design.

The consensus among scientists regarding the period of time in which the new body plans appear is 5-6 million years. Biologically speaking, that’s a blink of an eye. You aren’t going that kind of complexity and innovation in such a short period of time any more than you can expect to win the lottery by buying 5-6 million tickets when the odds of winning are 1 in a googol (10 to the 100th power – 1, followed by 100 zeroes). You don’t have enough lottery tickets to make winning the lottery likely. Similarly, 5-6 million years is not enough time for naturalistic mechanisms to code brand new body plans from scratch. It would be like trying to research and write a Ph.D thesis during a single lunch hour. It’s just not enough time to produce the amount of information that’s required.

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5 Responses

  1. Or the “Cambrian period” was simply the first wave of Flood sediment deposited. The global Flood explanation would explain why there are few fossils in Precambrian sediments, but strata above the Precambrian are usually rich in fossils, have little to no erosion between them (because they were laid down within weeks or months of each other), and sometimes contain fossils that span multiple layers (hint: these organisms did not sit there being slowly buried for millions of years without decaying). It would also explain how so many soft-bodied organisms came to be fossilized (jellyfish, soft plant parts, etc). They had to be buried very quickly in order to fossilize before they rotted. A global Flood would also explain why there is some sorting of fossils, but also why there are many examples of fossils “out of sequence.” The mainstream explanation of the fossil record as a slow, gradual process of sediment accumulation over millions of years just doesn’t fit the evidence.

    Of course, the Cambrian explosion argument is stil a useful one as it shows that even the mainstream ideas about the fossil record don’t support Darwinian evolution. But that doesn’t mean there was an actual 5-10 million year period when the majority of animal body plans appeared.

  2. LuAnn says:

    i like your perspective, Lindsay…how do they date the Cambrian if you disagree with the time frame?

    • Young earth creationists use the same relative dating methods (superposition, cross-cutting, intrusions, etc) as everyone else to determine which layers are older or younger than others. But relative dating methods don’t give you an age, just a relationship to other layers.

      To get an actual age for a layer requires other methods, which are less reliable. One of these, which is usually considered fairly reliable, is radiometric dating. Of course, you can’t date a sedimentary layer directly with radiometric dating, but you can date igneous layers that intrude into or lie between layers and thus get dates for sedimentary rocks indirectly.

      However, there is evidence that there has been at least one period in earth’s history in which there was increased radioactive decay (i.e. the rates of radioactive decay have not always been what they are now). This conclusion was the result of a multi-disciplinary collaborative study known as the RATE project (Radioisotopes and the Age of The Earth). In short, there is evidence that millions of years’ worth of radioactive decay has occurred on earth (using today’s rates), but there is also evidence that it did not actually take millions of years to occur. There are conflicting “clocks” within the same mineral crystals that give conflicting dates, indicating that there is more to the story than simple radioactive decay at today’s rates. If radioactive decay rates have indeed been different in the past, as the evidence indicates, then traditional radiometric dating methods are inherently flawed and will give incorrect (even grossly incorrect) dates. It is on evidence such as this that young earth creationists reject the traditional dates given for sedimentary layers.

      One method that young earth creationists do use to give an approximate date for Flood sediments is to use the Biblical timeline (use of genealogies and known dates for major events) to estimate when the Flood may have occurred. This method, which is historical rather than scientific, gives an age of around 4500 years for all Flood sediments (which are generally considered to comprise the majority of the Geologic Column).

      • I think that if a person can support his family doing other things like Dr. Craig, then they should do that. I am just an average guy who wanted a normal marriage. So I chose a field where I could pay the bills and support Christian scholars, too. The big guys run on donations provided by ordinary guys like me.

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