Cambrian Explosion Paper
I wrote this paper tonight. My friend at school keeps nagging me about the Cambrian Explosion, saying it falsifies evolution. I decided to write him a nice paper to get him to do some research (though today he told me that he would not look at any more evidence, and if there was something to prove him wrong, he would still think the Cambrian Explosion could not be accounted for by evolution). Before I give him the paper, I wanted to kow what you guys thought of it. Any typos? Nonsensical sentences? etc.
The Cambrian Explosion
The purpose of this paper is to refute the claim that Evolutionary Theory cannot account for the findings of the Cambrian Explosion. This claim comes in two parts; one is that the Cambrian Explosion shows a rapid diversification of life; contradicting gradualism. The next is that Darwin?s ?Tree of Life? is destroyed when one looks at the Cambrian Explosion. This paper, then, will be split into four sections. The first will briefly describe what the Cambrian Explosion is. The second will comprise the refutations of the aforementioned claims, and the last segment will be a conclusion.
Defining the Cambrian Explosion
The Cambrian is a period of the Geologic Column that lasted from 542 million years ago (MYA) to 488.3 MYA1. The Cambrian itself is also broken up into three segments; Early, Middle, and Late. It is believed that during the Cambrian period the Earth was much warmer than it had previously been; a contrast with preceding ice ages. Of the three aforementioned sub-periods, the Cambrian Explosion happened during the Early Cambrian (542-530 MYA). The following is found: most modern animal phyla appear in the Cambrian without any hint of a predecessor. The large majority of the findings prior to the Cambrian are sponges. One should note that some of the modern animal phyla are not represented in the Early Cambrian, or anywhere in the Cambrian. These phyla are of soft-bodied organisms. Recently, Creationists and advocates of Intelligent Design have tried to skew the results of the Cambrian Explosion to try and demonstrate ?flaws? in Evolutionary Theory that it supposedly cannot account for. What the next few paragraphs will demonstrate is that Evolutionary Theory certainly can account for the results of the Cambrian Explosion, and that to conclude otherwise is to ignore evidence.
Reconciling Rapid Diversification with Gradualism
The first item to address is the sudden appearance of most animal phyla. This must be reconciled with gradualism. One should note that 1) every single plant phyla has no record of existing in the Cambrian2. 2) Cnidarians (e.g. jellyfish, corals) and sponges appear prior to the Cambrian3. Byrozoans (marine invertebrates that grow in colonies) have no record in the Cambrian, and one source has stated that 22 metazoan (eukaryotic, or multi-cellular) phyla either do not have a record, or do not show up during the Cambrian4. Next, one should note that it is not clear when the Cambrian Explosion lasted, or when it began. However, it is clear that it lasted at least 5 million years, and perhaps as long as 40 million years. Though this is faster than the average pace of evolution, it is by no means a leap. There are also many plausible explanations (I will mention just three) as to what caused the Explosion.
One possible explanation proposed by von. Bloh et. al5, is that plants helped to create a favorable climate in which complex, multi-cellular life could exist. As stated before no plant fossils exist before or during the Cambrian, however, there is genetic evidence6 of simple plants like algae existing. Climatologists believe that there were excessive amounts of C02 in the atmosphere around this time, and that this created a greenhouse effect that created very high temperatures on Earth, perhaps at or higher than 30?C (86?F). A global temperature such as this would not be very hospitable to diverse life forms. However, with algae taking in C02, thus weakening the greenhouse effect, the temperature decreased, perhaps by 15?C in 40 MYA7. This temperature decrease would be more hospitable to complex life, which has a lower tolerance in terms of temperature. This temperature increase is also backed by findings in Ediacaran strata, a geological period just prior to the Cambrian. Here we find a chemically distinct carbonate layer that is indicative of the end of a global ice age8. Another explanation, a view held by Tim Lenton9 is that life could only diversify when oxygen levels increased. This would naturally occur with the photosynthesis of plants and oxygen-producing bacteria.
Another hypothesis is that the Hox gene, which is very important in determining morphology (basic body structure)10, was likely evolving during this time. Duplication of Hox genes can result in entirely new body segments11, these duplications, given a wide variety of climates, will support varying body types, which would lead to the diversity of life seen in the Cambrian Explosion.
Lastly, there is the hypothesis that much of pre-Cambrian life was microscopic. Various geologic strata but mainly the Doushantuo Formation in China provide evidence for this hypothesis. The Doushantuo Formation, while holding many sponges, also holds several embryonic bilaterians (creatures exhibiting some form of bodily symmetry). Most of these embryos are microscopic, some among the order of 750?m. There could very well be many fossils prior to the Cambrian that are ancestral forms of the creatures we find in the Cambrian Explosion; they might simply be the microscopic forms we have found in strata like the Doushantuo Formation.
The point here is to demonstrate that the Cambrian Explosion does not create a single problem with Evolutionary Theory. I?ve simply listed a few hypotheses of many as to what caused the rapid diversification of life. Scientists have known about this explosion for decades, and yet no more than a handful (if any) have decided Evolutionary Theory was wrong based on this. Having decided to merge the claim about gradualism with that of the new ?tree of life? picture that Creationists say the Cambrian Explosion ?invalidates?, it should be clear that this is a falsehood. Fossilization is no easy process: a creature must die and be buried rapidly before it can be eaten by predators. Next, permineralization must occur; a process that involves slow replacement of organic matter with minerals. Though soft tissue can fossilize, it is less likely than hard parts13 such as teeth and shells, both of which first appear during the Cambrian14. The fossils that we do find in the pre-Cambrian (e.g. arthropods and halkierids (a metazoan)), perfectly match predictions regarding transitional fossils15. Genetic evidence also contributes to evolutionary predictions of common ancestry, plants having diversified from the common ancestor prior to the diversification of animal and fungi kingdoms16.
In sum then, it has been demonstrated that the Cambrian Explosion creates no problem for evolution. Though scientists are well aware of the existence of the Cambrian Explosion, they also have a number of plausible hypotheses as to its cause, all of which do not violate natural selection; none of which support Creationism or Intelligent Design. To argue that the Cambrian Explosion is somehow evidence for the latter, or against the former, is to not understand what actually occurred in the Cambrian and pre-Cambrian eras.
 Most information in the initial paragraph was from http://en.wikipedia.org/wiki/Cambrian
[2-4] http://talkorigins.org/indexcc/CC/CC300.html, CC300 Cambrian Explosion
von Bloh, W., C. Bounama, and S. Franck (2003), Cambrian explosion triggered by geosphere-biosphere feedbacks, Geophys. Res. Lett., 30(18), 1963, doi:10.1029/2003GL017928
[14-16] http://talkorigins.org/indexcc/CC/CC301.html, CC301 Cambrian Explosion and Evolutionary Branching