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Cambrian Explosion

It is good to get to the bottom of a story. Let us then proceed down to earth’s bedrock above which all sedimentary rocks lie. The origin of sedimentary rock is particles eroded initially from molten rock. The particles may be of various sizes from very fine clay particles, to sand and gravel and boulders. As we move upward through the sedimentary rocks, we encounter traces of once living organisms, or of the fossilized organisms themselves. Thus, we find microbes and algae and other single celled organisms, and then some multicellular organisms with very strange features. Mostly people think they might be plants or lichens. (Lichens are a symbiotic association of an alga and a fungus.) This particular collection of rock strata is called the Ediacaran Biota and it lies immediately below the Cambrian rocks.

The Cambrian rocks are very different from the lower lying Precambrian rocks. For a start, they are in many places marked by a “Great Unconformity” a dramatically eroded surface under the Cambrian rocks. A cover story in Nature tells us about this point in the rocks. “The Great Unconformity is well exposed in the Grand Canyon, but this geomorphic surface, which records the erosion and weathering of continental crust followed by sediment accumulation, can be traced across Laurentia and globally, including Gondwana, Baltica, Avalonia and Siberia, making it the most widely recognized and distinctive stratigraphic surface in the rock record. It is also notable because the Cambrian sediments that overlie it in many regions preserve the first skeletonized crown-group of animals…”  [Shanan E. Peters and Robert R. Gaines. 2012. Formation of the ‘Great Unconformity’ as a trigger for the Cambrian explosion. Nature 484 pp. 363-366. See p. 363 emphasis mine] It is notable that this erosion surface, at this level, is a worldwide phenomenon and above it lie the first multicellular animals. That fits flood geology, by the way. [Gondwana = southern continents; Baltica = northwest Europe; Avalonia= Great Britain to eastern North America; and Siberia = western North America to Russia]

The above quote about the Great Unconformity says it all. In Cambrian rocks, all of a sudden, most of the multicellular animal phyla appear as if from nowhere. No ancestors have been found in lower lying rocks. Estimates of the number of different body plans (or phyla) vary, but these range from about 14 to 30 different phyla. They appear so quickly that nobody can figure out how an evolutionary development could happen so quickly. The famous Stephen Jay Gould articulated the problem in terms of evolutionary long ages, which do not in the least eliminate the problem.  Thus, he said: “Nearly 2.5 billion years of prokaryotic cells and nothing else – two-thirds of life’s history in stasis at the lowest level of recorded complexity. Another 700 million years of the larger and much more intricate eukaryotic cells, but no aggregation to multicellular animal life. Then, in the 100-million year blink of a geological eye, three outstandingly different faunas – from Ediacara, to Tommotian, to Burgess [Cambrian explosion}. Since then, more than 500 million years of wonderful stories, triumphs and tragedies, but not a single new phylum, or basic anatomical design, added to the Burgess complement.” [Stephen Jay Gould. 1989. Wonderful Life: The Burgess Shale and the Nature of History. W. W. Norton & Company. pp. 347. See p. 60].

Scientists are still agreed that the sudden appearance of all these complex animal body plans (including vertebrates or animals with a backbone) is something they cannot explain. One recent author thinks he can explain some of the problems by means of epigenetic marks on the DNA of ancestral creatures. This sounds most unpromising. As he himself admits, scientists have few answers to some big problems. He firstly admits that the Cambrian explosion “continues to be one of the greatest enigmas of modern biology.” [Nelson R. Cabej. 2020. Epigenetic Mechanisms of the Cambrian Explosion. Academic Press. pp. 258. See p. x]

Cabej tells us that the usual explanations for evolutionary progress such as gene mutations, gene recombination, and drift simply are inadequate to explain anything in this case. He remarks that people talk about environmental changes, but, he says, these cannot address the issue of how to bring about major changes which can be inherited.  None of the mechanisms suggested as causative agents, he says, “explains how the change in the environmental temperature, oxygen content, sea salt, even predation, etc., might lead to evolutionary changes and formation of new species or Bauplan [body plans].” [p. xi]

The crux of the matter, Dr. Cabej declares is that we need an agent with information! Thus in an astonishing admission he declares: ““We need to address the key question: “Which is the ‘user of the genetic toolkit’?’ determining expression and recruitment of genes and gene regulatory networks (GRNs) during phylogeny and how basically the same genetic toolkit generated the breathtaking diversity of forms during the Cambrian.” [emphasis mine p. xi] He implies that it was an agent using information which was able to use the same basic set of genes to produce amazingly different body plans. Here Dr. Cabej mentions the need for information to drive the process. “The fact that all these processes, do not occur randomly or casuistically, but instead in strictly determined sites and times, indicates that information of some kind, but obviously different from the genetic information for protein biosynthesis, is used to produce them.” [emphasis mine p. xii]

The animals that we see in Cambrian deposits are not simple creatures. They are sophisticated, representing many lifestyles like scavengers, filter feeders, grazers, predators and top predators. Prominent representatives of the Cambrian community include Anomalocaris and its relatives, top predators with fancy devices for catching prey and very sophisticated large compound eyes. Some of these animals were as much as one metre long.

The Cambrian explosion is just one of many gaps, sudden appearances of organisms in the fossil record without any ancestors lying below (preceding them) in the fossil record. Intelligent design advocates suggest that an intelligent designer inserted the necessary information into organisms to bring about a very fast evolutionary process. As creationists, we interpret this information differently. To us, the Great Unconformity underlying the Cambrian rocks, is a mark of the onset of violent flood waters eroding molten and sedimentary rocks and burying nearby marine creatures. The great diversity of creatures in Cambrian rocks, and their highly sophisticated designs, testify to a complete ecology with producers, grazers, predators and top predators all present in the same communities which were overcome by the flood waters.

Related Resources

Related Terms

  • Body Plans
  • Evo-Devo
  • Sedimentary Rock
  • Sudden Appearance
  • Molecular Clock
  • Information
  • Burgess Shale
  • Epigenetics