TheCambrian Explosion

Discussion in 'Creation vs. Evolution' started by Administrator2, Jan 21, 2002.

  1. Administrator2

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    HELEN
    For those who think the Cambrian Explosion is a ‘creationist problem’:

    As the Scientific American Website http://www.sciam.com/explorations/082597cambrian/powell.html
    explains it,
    "Fossils locked away in rocks from the Cambrian Period record one of the most astounding episodes in the history of evolution. Beginning 540 million years ago, life on the earth took on radically new forms. Nearly all of the major groups (phyla) of animals that we see today arose at that time. The change was as rapid as it was complete, with much of the evolutionary innovation taking place over as little as five million years; scientists often refer to this period as the 'Cambrian explosion'."

    Or, in the words of a professor on the internet:
    "One of the most difficult problems in evolutionary paleontology has been the almost abrupt appearance of the major animal groups--classes and phyla--in full-fledged form, in the Cambrian and Ordovician periods. This must reflect a sudden acquisition of skeletons by the various groups, in itself a problem."
    http://www.colorado-mall.com/HTML/EDUCATIONAL/SCIENCES/PALEONTOLOGY/paleontologyIntr
    o.html

    These are just two quotes from sources from the evolution side out of, literally hundreds, of references to the problems posed evolutionarily regarding the Cambrian explosion.


    QXR37
    Here's some info on the Cambrian explosion someone posted on another board at http://www.arn.org/ubb/Forum1/HTML/001007.html

    The post below is one I wrote way back in May of 1997 that debunks a variety of assertions about the Precambrian/Cambrian transition period most notably by Phillip Johnson. It was originally written in response to a cut-n-paste job by JackW of Phillip Johnson's assertions, but the thread is still quite relevant. Despite the fact that I've reposted it at least 3 times it seems that old, outdated ideas die hard. For those of you who have seen it the previous 3 TIMES, please excuse the repetition.

    "Once in a while people post things on this board that they do not understand because they are not intimately acquainted with the facts. As we have seen, eveyone here has their pet topics and I'm pleased to announce that Jack has posted one right dead center in the middle of the very research I conducted for my Ph.D and I couldn't be happier! No digging through books trying to find obscure quotes or trips to the library-- I get to just consult my own materials! Hooray!

    Anyway, here's the scoop:

    Jack's post of Johnson's "Darwin on Trial" discusses the "Cambrian explosion", the supposed sudden appearance of dozens of phyla in a geologic wink of an eye and how it presents some sort of tremendous challenge for evolution. For example, in Jack's Part 6 Johnson is quoted as saying:

    "Unicellular life had existed for a long time, and some multicellular groups appear in the immediately Precambrian rocks, but there is nothing that can be established as ancestral to the Cambrian animals."

    Later, Johnson adds:

    "A mysterious process that produces dozens of complex animal groups directly from single-celled predecessors, with only some words like "fast-transition" in between, may be called "evolution" -- but the term is being used more in the sense of Grasse's heresy than of Dobzhansky's Darwinian orthodoxy. Each of those Cambrian animals contained a variety of immensely complicated organ systems. How can such innovations appear except by the gradual accumulation of micromutations, unless there was some supernatural intervention? It is not only that the Darwinian theory requires a very gradual line of descent from each Cambrian animal group back to its hypothetical single-celled ancestor. Because Darwinian evolution is a purposeless, chance- driven process, which would not proceed directly from a starting point to a destination, there should also be thick bushes of side branches in each line. As Darwin himself put it, if Darwinism is true the Precambrian world must have "swarmed with living creatures" many of which were ancestral to the Cambrian animals. If he really rejects the artifact theory of the Precambrian fossil record, Gould also rejects the Darwinian theory of evolution. [Careful readers will note that the non-existence of the Cambrian ancestors is vaguely qualified by the phrase "at least as complex invertebrates easily linked to their descendants." I have learned to be alert to this sort of qualification in Gould's writing, because it signals a possible line of retreat. I have reason to believe that Gould would repopulate the Precambrian world with invisible ancestors, and thus re-embrace the artifact theory, if he were accused of abandoning the mutation/selection mechanism and thus leaving the evolution of complexity unexplained.]"

    Johnson didn't do his homework. His ideas about the Precambrian fossil record are just plain wrong. Here's what we actually know:

    The appearance of some complex animals in the Cambrian is indeed interesting, but no great mystery. Research conducted *since*1989 (When Gould's "Wonderful Life" was published) by myself and others has demonstrated two grave errors in Johnson's depiction of the Precambrian-Cambrian transition:

    1) His representation that no Precambrian animals are found in the Cambrian is incorrect.
    Finds by Desmond Collins of the Royal Ontario Museum have been made of several taxa morphologically identical to species found in the Precambrian of Australia. In particular, his find of a creature called Metaspriggina is especially important, because the Precambrian creature Spriggina shows sufficient similarity to the arthropod body plan that it is certainly a basal member of the group. Not only does the discovery of Metaspriggina bridge the "gap" between Precambrian and Cambrian, it also demonstrates that arthropods developed a hard exoskeleton almost 30 million years *after* their earliest confirmed appearance in the fossil record. This leads to the second of Johnson's flaws:

    2) Johnson's claim that Cambrian-type animals appear suddenly is false.
    Since the 1980's it has been known that the very lowest interval of the Cambrian contains only the fossils of tiny spines and tubes barely visible to the naked eye. Trilobites and other complex animals are nowhere to be found, but the spines were obviously made by something. It has also long been known that trace fossils (the trails and tracks and burrows made by organisms) exist below even the oldest body fossils of Precambrian animals and have been dated to almost 700 million years.

    Experimental studies of the traces made by living organisms have found a very interesting phenomenon that has unlocked the secrets of earliest Precambrian trace fossils. It turns out that animals need to reach a certain stage of cellular complexity before they can burrow and this has very interesting implications in the Precambrian. Diploblastic animals (those with only two germ layers) such as sea anenomes must move by a simplistic mechanism that makes it impossible for them to burrow deeply. Biomechanical studies have found that this limitation is due to the fact that diploblastic animals cannot build the kind of walls within the body cavity required for creating rhythmic burrowing motion. In other words, unless you have at least three germ layers like everything from bugs to bears, you're confined to the surface of your world.

    So what about those trace fossils? The sequence of trace fossils found below and above the body fossils of the Precambrian animals of the Ediacaran Fauna shows something very interesting. Below the animal fossils there are no deep burrows, only surface trails characteristic of those made by diploblastic animals-- no traces of legs or feet, but drag marks identical to those produced by the animals under study. Above the animal fossils, there are deep burrows, trails made by things with feet and other complex feeding trails strikingly different than those below.

    The timing of these events shows that this change took place in an interval between 700 million years ago and 550 million years ago, with the animal fossils of the Ediacaran Fauna located in an interval of about 70-80 million years wide beginning at about 630-620 million years ago. The conclusion is obvious. In the minimum1 30 million years prior to the Cambrian, animals with only a single germ layer (unicellular animals can form colonies, but without differentiating into distinct cellular layers) were followed by animals with two germ layers and finally the triploblastic form characteristic of virtually all living multicellular life.

    Remember those tiny mystery fossils I mentioned earlier? In 1990 and 1991, discoveries made at Sirius Passet in Greenland found the oldest known complete soft-bodied Cambrian animals. It turns out that the tiny spines and tubes were actually fragments of animals that were mostly soft-bodied, but which possessed a few mineralized parts. Most of these soft-bodied animals were creatures with an arthropod body plan, but a number of others show distinct similarities to many Precambrian taxa. It was clear from these finds that the transition from Precambrian to Cambrian marked the first invention of biomineralization (the ability to make hard parts) more than the invention of body plans.

    What does this tell us about the "Cambrian Explosion"? Since multicelled, diploblastic animals existed at least 130 million years prior to the base of the Cambrian, since the transition to triploblastic animals had at least 50 million years head start and the Sirius Passet Fauna showed that the Cambrian actually marks the invention of mineralized skeletons and not the invention of body plans, it seems that the explosion is more of a fizzle than a bang. 130 million years ago dinosaurs roamed the Earth, mammals were little more than rodents and birds still had teeth and fingers. Grass would not evolve for another 30 million years and virtually no modern flowering plants had yet appeared. If we can go from dinos to dishwashers in 130 million years, it doesn't sound so hard to go from blobs to Burgess Shale in the same length of time does it?

    Before anyone jumps in to claim that Johnson is only parroting Gould you might also note that he sets up a strawman using Gould (and the CA Academy of Sciences) as a representation of the supposed facts that have "overturned" Darwinian gradualism and claiming them to be incorrect. Unfortunately, he fails to point out the numerous ancestors of Cambrian animals that have been described between the time Gould published and when Johnson published his own book. Was he too busy to look up the evidence or was it perhaps damning to his own pet ideas and thus worthy of being ignored?

    Johnson states:
    "The two graphics in Figure 1 illustrate both the problem the Cambrian Explosion poses for any theory of evolution, and the way a museum exhibition attempts to control the damage. The Exhibition is titled "Life Through Time: The Evidence for Evolution," and it is at the California Academy of Sciences Museum in Golden Gate Park in San Francisco. The lower diagram shows only the evidence, with the phyla appearing on parallel lines and absolutely no evidence of any common ancestors or transitional intermediates. The museum exhibit represented by the upper diagram adds the common ancestors and alters the vertical dimension representing the age of the fossils, in order to give the impression that the recalcitrant data constitute the required "evidence for evolution." At the intersection point where the common ancestors ought to be, the curators have placed magnifying glasses. Similar devices are used elsewhere in the exhibit to mark tiny animals or fossils. Unsophisticated museum visitors are likely to get the impression that the invisible common ancestors are known to science, but just a little too small for the naked eye to see. By such means even a spectacular example of absence of evidence for evolution can be transformed into evidence for evolution, and even evidence for the creative power of natural selection."

    Since at least 2 of the researchers in my references on this topic (see the last part of this post re: Valentine and Waggoner) have been on the faculty at UC Berkeley the entire time since "Wonderful Life" was published and since their offices are less than 300 yards from Johnson's, it seems puzzling that he never bothered to walk across campus to talk to two of the leading researchers on the topic as they have always disagreed with Gould and do not consider "Wonderful Life" to be the authoritative work on the Precambrian-Cambrian transition. Indeed, the Precambrian mollusc described by Fedonkin and Waggoner which Johnson claims doesn't exist (remember-- he said there are no ancestors of Cambrian taxa in Precambrian rock) was collected in 1991 and has been available for examination in the Museum of Paleontology at Berkeley all this time! Valentine is on record as saying that "Wonderful Life" was published prematurely as so many new discoveries were being made at the time it was written. Valentine and Waggoner both agree with Gould on most of the issues raised in "Wonderful Life" such as Walcott's methodology, the role of extinction in determining clade shape and the falsity of the notion of "progress", but they have always disagreed with Gould on the timing and rate of diversification at the base of the Cambrian.

    Funny that Johnson didn't think their ideas were worth mentioning, especially since they are not cheerleaders for Gould. Of course, they would have told him his ideas were full of serious lapses of fact so maybe it was best that he stayed in his office. After all, you can't let facts interfere with a good story can you?



    I might also add that in just the year and a half since I wrote the original, a variety of new things have been found that further erode the 1989 version of the "Cambrian Explosion" to the point that the concept is simply false. First, even more Ediacaran taxa have been found in the Cambrian including Swartpuntia (another one of the "frond-like" animals) as well as several more of the discoid taxa. One find is especially interesting in that it comes from the Late Cambrian of Ireland-- 50 million years younger than the beginning of the Cambrian itself!

    In addition, more Cambrian taxa continue to be found in the Precambrian. I've previously mentioned the trilobite-like creature discovered by Jim Gehling and shown in National Geographic from April 1998. Another similar beast has been discovered in Morocco and this one is the size of a compact disc!

    Finally, trace fossil work done since my own continues to push back the timing of events to the point that it coincides to a greater and greater degree with the molecular data (surprise!). The 1998 findings by Seilacher of traces almost a billion years old are still hotly debated, but are one of several much older suites of traces that all hover in the 700-900 million year old range. Trace fossils from Sonora, Mexico already conclusively pushed the date back to around 750-800 million years.

    In short, the fossils conclusively show that the origins of modern animal groups are spread over a vast stretch of time in the very distant past. Overlap between the Precambrian and Cambrian faunas shows that the transition is no more unusual than any of the myriad changes in communities over the remaining 500 million years. Certainly, many Ediacaran taxa are still quite mysterious and considering that they were soft-bodied they are likely to continue to be, but the pattern of appearance and extinction itself can no longer be seen to be "aberrant". No atom-bomb exploding, just lots of really great fireworks shows.

    References:
    Bud, G 1993 A Cambrian gilled lobopod from Greenland, Nature v.364, p.709-711

    Conway Morris, S 1993 The Fossil Record and the Early Evolution of the Metazoa, Nature v.361, p. 219-225 (Note that the Precambrian Spriggina is on the cover!)

    Conway Morris, S 1993 Ediacaran-like fossils in Cambrian Burgess Shale faunas in North America. Paleontology v.36, #3 p. 539-635
    Note also that Conway Morris described two new Precambrian-type fossils found in the Burgess Shale in the Journal "Paleontology" in 1994 and 1995. Other specimens are still being described.)

    Crimes, TP 1994 The Record of Biotic Changes Across the Precambrian-Cambrian Boundary in Donovan, SK (ed) The Paleobiology of Trace Fossils, London, Wiley Pub.

    Fedonkin, M and Waggoner, B 1996 The Vendian Fossil Kimberella: The Oldest Mollusk Known, Geological Society of America, Abstracts v. 28 #7, p. A53

    Valentine, JW et al. 1996 Developmental Evolution of Metazoan Body Plans: The Fossil Evidence, Developmental Biology, v.173, p.373-381

    Valentine, JW, Awramik, WSM et al. 1991 The biological explosion and the Precambrian-Cambrian boundary in Evolutionary Biology 25 (Hect, Wallace and MacIntyre eds.) p. 279-356

    And a few new ones:

    McMenamin, M 1998 The Garden of Ediacara, Columbia University Press
    (The ONLY non-specialist book ever written on the Ediacaran biota. Although McMenamin has an ego the size of Texas, his book is extremely well written in an almost "travleogue" style that is refreshing and fun. Highly recommended!)

    Narbonne, G et al. 1998 The youngest Ediacaran fossils from South Africa, Journal of Paleontology 71:6, p.953-967

    Conway Morris, S 1998 The Crucible of Creation, Oxford University Press
    (Another excellent book on the Burgess Shale by one of it's most prolific researchers. It also includes pictures of the Sirius Passet fauna as well as lots of extra detail about other Burgess-type sites.)


    HELEN
    I’m not sure that a critique of Philip Johnson is actually evidence of a lack of problems in the Cambrian Explosion…

    [ January 21, 2002: Message edited by: Administrator ]
     
  2. Administrator2

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    HELEN

    There have been those who proclaim that the Cambrian Explosion was not an
    'explosion' at all and that there was nothing puzzling about it.
    That, however, is not how the Smithsonian is billing their new traveling
    exhibit...
    "Burgess Shale: Evolution's Big Bang" is the name of the Smithsonian
    Institution's National Museum of Natural History's traveling exhibit.

     
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    JOE MEERT

    Helen continues to assert that the Cambrian explosion is a complete
    mystery to geology and therefore challenges evolution and cites (as
    evidence) the title of a traveling exhibit. The assertion is wrong on
    several counts, but let me discuss a couple of points (expanding on
    those above). The 'explosion' is referred to as an 'explosion' by some
    within the geologic community and as a 'slow burn' by others. At issue
    (still) is whether or not we are seeing a preservational bias or an
    actual blossoming of life in the 50+ MILLION YEARS leading to Toyonian
    time ( http://www.clas.ufl.edu/users/jmeert/cambrianc.jpg ). The
    verdict is not yet rendered despite the claims of creationists. I call
    your attention to several recent articles and discussions of this
    subject.

    1. Simon Conway-Morris: The Cambrian Explosion: A popular delusion
    (1999)
    2. Richard Fortey, Science 2001 The Cambrian Explosion: Exploded.

    Levinton and Wray (1999) note:

    McMenamin (1998) discuss the incredibly rich fossil record from the
    Ediacaran fauna which date back to at least 575 Ma so there is an
    incredible fossil record before that recorded in the Tommotian-Toyonian
    interval. The argument about the fossil record is lively, but certainly
    not damning for the subject of evolution. However, it is a very
    difficult thing for creationists to explain. If the creationists accept
    the notion of the fossil record in the Cambrian explosion (which they
    must in order to claim it is a problem), they must have an alternative
    explanation. This 'alternative explanation' for the fossil record from
    ~575-510 Ma, as I see it, can make one of two claims. The first claim
    is that these fossils represent organisms killed in the Noachian flood
    and the other claim is that it marks a 'sudden creation' event. Neither
    can be wholly satisfying for creationists. In the latter case (sudden
    creation) it must also mean 'sudden death' for these are fossils of
    organisms and therefore there must be death before the fall. In the
    former case (Noachian Flood) it would argue that this sequence of rocks
    marks the initiation of the global flood. The problem with that is that
    we have pretty clear evidence of paleosols and very dry environments
    within the same sequence of fossils housing the Ediacaran and Cambrian
    biota. Therefore, the flood explanation is lacking in evidence for a
    truly global flood. The hope of creationists is that by pointing out a
    perceived weakness in the evolution of phyla that no one will notice
    that their own explanation is wanting. In short, they have no clear
    explanation for the fossil record is telling them either (which they
    accept in this case)!
     
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    EARL DETRA

    Helen says:
    I’m not sure that a critique of Philip Johnson is actually evidence of a lack of problems in the Cambrian Explosion…


    Helen, if that is all you got out of the post. I think you need to reread it. For example, QXR37 says:

    "I might also add that in just the year and a half since I wrote the original, a variety of new things have been found that further erode the 1989 version of the "Cambrian Explosion" to the point that the concept is simply false. First, even more Ediacaran taxa have been found in the Cambrian including Swartpuntia (another one of the "frond-like" animals) as well as several more of the discoid taxa. One find is especially interesting in that it comes from the Late Cambrian of Ireland-- 50 million years younger than the beginning of the Cambrian itself!

    In addition, more Cambrian taxa continue to be found in the Precambrian. I've previously mentioned the trilobite-like creature discovered by Jim Gehling and shown in National Geographic from April 1998. Another similar beast has been discovered in Morocco and this one is the size of a compact disc!"


    There is not a word that is derogatory of Johnson in these two paragraphs and much of the rest of the text is similar. Perhaps you think that showing someone is wrong is some kind of personal attack, but in this case you are just being given information that you don't like. These are ideas that have been floating around geology for many years and they are contrary to Johnson's ideas. I'm not sure what your beef is.

    You go on in your next post to decry the Smithsonians depiction of the Cambrian explosion. Obviously, this material is sensationalized, but I would like to hear how they explain it rather than just your abstracted quote. Regardless, do you expect all evolutionists to be in lock step, just as creationist aren't? Clearly, QRX37, Joe and myself have made numerous comments that the Cambrian Explosion is overblown (so to speak). This should not be a new idea to you.

    So, what is your point in all this. Is the Smithsonian wrong or are they right? Is the Smithsonian right that PE is correct such that sudden leaps can be made in evolution, or are they wrong and Precambrian to Cambrian evolution was more gradual? Are you saying that because evolutionists disagree or that some may be out of date on mechanisms, that evolution fails in some respect? If so, you really need to look at the divisions within creationism or within Christianity itself. I think you will see that this line of questioning is really fruitless.
     

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