The Truth on the Cambrian “Explosion”
The fifty-three million year period known as the Cambrian is important to the fields of geology and biology because that was when many major groups of kinds of creatures with hard parts and shells, appear in the fossil record. This has been called the “age of trilobites” which were marine arthropods. — During this period of time, there was a unique episode in the history of life, an apparent evolutionary radiation in which life seems to “explode” in the fossil record. Complex marine animals with hard, preservable parts appear over a rapid span of time in the geological record. This event has been called the Cambrian “explosion.”
At the time Charles Darwin published Origin of Species in 1859, the fossils in the Cambrian were the oldest known ancient life, and paleontology and research in the fossil record hadn’t advanced as much as it has recently. — Darwin himself commented on it saying,
To the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, I can give no satisfactory answer. . . . Nevertheless, the difficulty of assigning any good reason for the absence of vast piles of strata rich in fossils beneath the Cambrian system is very great, and may be truly urged as a valid argument against the views here entertained.
Darwin’s statement, that the lack of fossils before the Cambrian, could be used as “a valid argument” against his theory has struck a chord with critics of Evolutionary theory into the present. In fact, it is hard to find many Intelligent Design and Creationist publications that do not talk about the apparent lack of fossil life before the Cambrian, using it as a “refutation” of Darwinian Evolution — “Darwinism,” as they call it. The apparent radiation of life that occurred called the Cambrian “explosion” is what they appeal to saying that this was the fauna in this strata appeared “all of a sudden, with no evolutionary ancestors.” —
If it could be shown that animal species, in fact, appeared without any kinds of evolutionary ancestors, then Evolutionary Theory would be in trouble. That is a fact. However, if the scientific literature were to show that these fauna had viable ancestors, then there is no problem for the scientific consensus.
First of all, it should be pointed out that the Cambrian “explosion” was only explosive in geologic terms. It is usually estimated to have lasted between 10 to 25 million years —- which is a far cry from the impression that Intelligent Design proponents attempt to give when they say that phyla appear “all of a sudden.” Though rapid in geologic terms, it is hardly rapid on the time scale, and it is not far-fetched to allow plenty of evolution within that time period. It would appear that Antievolutionists are confused by the usage of the word “explosion.”
The claim that phyla appeared “all of a sudden with no viable ancestors” would also be damaging . . . if it were true. But it is not. There is sufficient evidence for animal life before the Cambrian explosion:
- Complete fossil embryos pre-dating the Cambrian “explosion” by 10 million years were discovered in 2006, and show that animal complexity was already starting to bloom. Fossil embryos are a rare enough find without them being complete.
- There are plausible pre-Cambrian ancestors for trilobites. For example, there are the Spriggina floundersi, the so-called “Soft-bodied trilobite,” as well as Parvancorina. — Parvancorina is classified, interestingly enough in the Kingdom Animalia, and was possibly even an arthropod. — Also, to make matters worse, there are many transitions between trilobites which are extremely diverse and themselves indicate plenty of Evolution, not just during the 300 million years of their existence, but also during the Cambrian period.
- Even if non of the examples listed in the last example above were not arthropods or ancestral to trilobites, there is still proof that arthropods did in fact exist before the Cambrian period. Arthropod trace fossils have been found in Nevada in strata dating to 30 million years before the Cambrian, proving that there were animals with legs much earlier than once thought. — Amusingly, some Creationists have attempted to use this one example to refute the Evolution timeline not realizing that this find did more harm to the Creationist argument of the Cambrian “explosion.”
- There is new fossil evidence of bilateral animals which was recovered from the Doushantuo Formation in China dating from between 40 and 55 million years before the Cambrian. The specimen, called Vernanimalcula, had features like a mouth, a gut, an anus as well as surface pits. This would itself show the Cambrian was not the starting point for complex life.
- Newly discovered “chemical fossils” have demonstrated evidence that Sponges, as the first Animal life, had already existed around 635 million years ago, or between 90 to 100 million years before the Cambrian “explosion.”
- The Cambrian “explosion” just doesn’t stand up to the genetic evidence. Molecular clocks indicate a more ancient starting point from between 800 million to 1.2 billion years. This indicates that the fossil record has plenty of gaps, though genetics seems to compensate for what is lacking to a certain extent.
Another detail to consider is that it is plausible that, even though speciation seemingly did pick up during the radiation, it is may in fact not be anything special when compared to other similar radiations that occurred. — Using trilobites as a statistical basis, Bruce S. Lieberman concluded that “speciation rates among olenellid trilobites in the Cambrian radiation were not unusually high.” He then also said that if these results can be extended to other groups, then special rules aren’t necessary to explain the Cambrian “explosion.” — This, in my opinion, falsifies the Creationist impression of rapid and sudden appearance.
Since it is widely agreed by biologists that the Cambrian “explosion” was a real event, there remains the problem of attempting to explain what caused it, and these explanations are controversial in the scientific community. Plenty of them have to do with environmental changes such as “Snowball Earth”, and also some have proposed that an increase in levels in oxygen in the atmosphere allowing big-bodied animals to thrive. This second proposal could fail assuming that the big-bodied Ediacaran fauna (existing 30 million years before the Cambrian) are in fact animals. One model indicates it -as well as other radiations- may have “changes in the pattern of gene regulation.” On the other hand, indications show that Hox and other developmental control genes were already in existence before the radiation, though genomic repattering during the early Cambrian which involved some key genes and regulators.
But then again, there are scientists that are starting to question whether or not it was even a real event based pre-Cambrian fossil evidence as well as genetics, a lot of which is given above. Naturally, if this is the case, then there is no need to explain it, much less resort to the supernatural.
Any objective look at the Scientific evidence shows that the so-called Cambrian “explosion” cannot be used as evidence for a “creation event” because of its suddenness. As a matter of fact, some of the fossil finds would seem to muffle the “explosiveness” since it is now clear that complex life existed at least around 40 to 55 million years before. The implications of this is that there are possible evolutionary ancestors to the Cambrian multicellular life. — Antievolutionists should update their claims if they want to retain any credibility.
The Cambrian Period: An Explosion of Life, from fossils-facts-and-finds.com
Trilobites, from C&J Fossils.
Frequently Asked Questions About Evolution, from PBS.org.
Embryo Fossils Reveal Animal Complexity 10 Million Years Before Cambrian Explosion, from Physorg.org
Origins of Trilobites by S.M. Gon III. From Trilobites.info.
Earliest Footprints Ever Found, from RESEARCH.
Signs point to sponges as earliest animal life, from MIT News.
Evolutionary Trends in Trilobites, by S.M. Gon III, From Trilibites.info.
Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian, by Jun-Yuan Chen, David J. Bottjer, Paola Oliveri, Stephen Q. Dornbos, Feng Gao, Seth Ruffins, Huimei Chi, Chia-Wei Li, and Eric H. Davidson. From Science. Also, see The Early Evolution of Animals by David J. Bottjer, from Scientific American.
Molecular Clocks Do Not Support the Cambrian Explosion, by Jaime E. Blair and S. Blair Hedges, from Oxford Journals.– Also see Testing the Cambrian explosion hypothesis by using a molecular dating technique, by Lindell Bromham, Andrew Rambaut, Richard Fortey, Alan Cooper, and David Penny. From the Proceedings at the National Academy of Sciences.
Taking the Pulse of the Cambrian Radiation, by Bruce S. Lieberman From Integrative and Comparative Biology.
Explaining the Cambrian “Explosion” of Animals, by Charles R. Marshall, from Annual Reviews.
Adaptive walks in a gene network model of morphogenesis: insights into the Cambrian explosion, by Solé RV, Fernández P, and Kauffman SA. From the International Journal of Developmental Biology.
Fossils, molecules and embryos: new perspectives on the Cambrian Explosion, by James W. Valentine, David Jablonski and Douglas H. Erwin.
Plant and Animal Evolution.
Transitional Forms and the Evolution of Phyla, by Glenn R. Morton, from American Scientific Affiliation. Published in Perspectives on Science and Christian Faith.
The Precambrian to Cambrian Fossil Record and Transitional Forms, by Keith Miller, from American Scientific Affiliation. Published in Perspectives on Science and Christian Faith.
Re:Cambrian Explosion, by Keith Miller, from the American Scientific Affiliation.