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The Cambrian Explosion

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  • Pages: 3
  • Word count: 726
  • Category: Animals

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            The Cambrian Explosion or Cambrian radiation was seemingly the sudden disappearance of a variety of complex animals. According to Con way (2006), the explosion took place about 540 million years ago on geological times. During this period, most major animal groups appeared for the first time in fossil records. The theory of Cambrian evolution holds that at the beginning of some 545 million years ago, an explosion diversity led to appearance within  a relatively short period of 5-10 million years of a huge number of complex, multi-celled organisms. The burst of these animal forms led to the most of the animal groups that we know today.

            Further studies by Conway (2006) reveal that the Cambrian Explosion is the outcome of changes in environmental factors leading to changes in selective pressures which in turn leads to adaptive diversification on a vast scale. By the start of Cambrian Explosion, the large super continent Gondwanaland comprising of all land forms was breaking up into smaller land masses. This increased the area of continental shelf, and also led to production of environmental niches in which animals could specialize.

            There has been a heated debate as to whether the Cambrian explosion was of sudden and spontaneous as it appears in fossil records. The long running puzzlement about the appearance of Cambrian fauna seemingly abrupt from nowhere has generated extensive scientific debate. The seemingly appearance of fossils was noted by Charles Darwin since it was a major objection to his theory of evolution by natural selection. According to Conway (2006), long puzzling explosion centers on three key points: whether there was really a mass of diversification of complex organisms over relatively a short period of time during the early Cambrian, what might have caused such a rapid explosion, and what it would imply about the origin and evolution of animals.  Interpretation of this explosion is difficult due to a limited supply of evidence based mainly on an incomplete fossil record and chemical signatures left by Cambrian rocks. Deducing the events of half a billion years might be tricky since the evidence comes from biological and chemical signatures in rocks. Studies reveal that the Cambrian dates can only be obtained through a detailed analysis of radio active elements that are contained in those rocks.

            Moreover, relative dating ‘A’ is used since it is more sufficient for studying the process of evolution. The pace of evolution was exceptionally fast in the Cambrian period. Possible explanations for the explosion falls under three broad categories: environmental, developmental and ecological changes. Studies by Conway (2006) reveal that changes in environmental includes, increased carbon dioxide levels and the presence of snow balls earth glaciations. Further, the earliest man atmosphere contained no free oxygen. The oxygen that animals breathe is as a result of a product of photosynthesis for billion years. Increase in oxygen concentration both in air and water increased the sizes that organisms grew at without their tissues being starved.  This facilitated growth in these organisms at a faster rate.

            Conway (2006) further argues that the developmental changes have led to minor modifications to animal development. This is because as animals grow from embryo to adult, there is a possibility that they might be able to cause changes to the final animal form. The ecological explanation focuses on the interactions between different types of organisms. When they interact, there is a rapid increase in disparity and diversity. The three factors above are the major possible causes of the Cambrian Explosion.


            The Cambrian Explosion is one of the most unique explosions in history. It can be viewed first as co-evolutionary rise in diversity as the animals explored the niches of Ediecaran sea floor, followed by a second expansion in the early Cambrian as they become established in the water columns (Conway, 2006). After reviewing of rocks near pre-Cambrian boundary, Bowring and his colleagues reported in 1993, that Cambrian explosion was unlikely to have exceeded 10 million years ago, since the time of Cambrian to the present day is one seventh of the time since the origin of life on earth. This explains that the Cambrian Explosion was geologically abrupt indeed.

Work Cited

Conway Morris, (2006). Philos Trans R Soc Lond B Biol Sci, Vol. 361, No. 1470., pp. 1069-1083.

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