The Cambrian explosion, and understanding geological history

High school geology classes were difficult, and also lots of fun. No, becoming a geologist was never the goal – education is not an ‘apprenticeship’; geology is not a garden implement or lawn mower that you study so you can ‘use it’ later. Purely career-oriented motivations are not the only reasons to take up science.

However, there is an important way that geology can be used, for lack of a better expression – countering the false claims, made by intelligent design proponents, regarding the Cambrian explosion. Let’s unpack this subject.

The vast majority of the Earth’s evolution is marked by the predominance of single-celled bacterial life. The apparently sudden appearance of nearly all the main body types of animal life around 541 million years ago – along with the evolution of multicellular life – seems like a major discontinuity.

This rapid diversification is referred to as the Cambrian explosion. Named after the Cambrian geological period, this ‘explosion’ purportedly presents a problem for evolutionary biology – except that it does not. Lasting between 13 and 25 million years, this apparent ‘explosion’ witnessed the divergence of all the modern metazoan phyla. Some biologists place the duration of the ‘explosion’ at 20 million years – a monumental length of time, but not uncommon when examining geological time. The Early Cambrian was 25 million years long – hardly a short time frame, so the label of an ‘explosion’ is a bit of a misnomer.

There are many unanswered questions regarding the causes and progress of the seemingly sudden appearance of major animal phyla during the Cambrian explosion. Scientists are debating its duration, and whether it is more accurate to call this episode a diversification or radiation of major metazoan phyla.

However, given these disagreements, let’s highlight one point – please stop using the episode to in the fossil record and biological evolution to pose a false challenge to the general validity of evolutionary theory. The term sudden appearance should not be used to sneak in the biblical Genesis story of creation as a supposed ‘verification’ of scripture.

There was rapid multicellular growth in the Cambrian, but this era did not mark the first appearance of multicellular life. Complex multicellular life preceded the putative Cambrian explosion by millions of years. There certainly are fossils, such as Anomalocaris, whose lineage cannot be traced directly to the Middle Cambrian. However, this does not prove the ‘sudden emergence’ of animal phyla in the Cambrian explosion. It was in this period that organisms became of extensively mineralised, increasing the amount of fossils left behind.

Indeed, the development of the field of geology – examining the bio-stratigraphic record of the Earth – was the major challenge upturning the biblical view of natural history, decades prior to the publication of Charles Darwin’s books on evolution. As geologists began to dig, especially in search of commercially viable oil deposits, what they found did not harmonise with a biblically-based account of the planet’s history. Conditions in the geological field compelled scientists to revise their previously cherished notions of a Genesis-compatible Earth.

Darwin himself realised the difficulty the rapid diversification of animal phyla in the Cambrian explosion presented for his theory of evolution by natural selection. The seeming rapidity of the rise of animal phyla apparently contradicted the prolonged, gradual and incremental change that evolutionary biology allegedly required. Findings in the field after Darwin’s death provided solutions.

The National Centre for Science Education (NCSE) published the findings of a team of geologists from the University of Adelaide, South Australia, who addressed this precise question. As the NCSE summarised:

Was the geologically fast diversification during the Cambrian too fast to be explained by normal evolutionary processes? Does the Cambrian explosion threaten the theory of evolution? To these questions researchers at the University of Adelaide offer a definitive answer: “No.”

The researchers concluded that even using the fastest inferred rates – and they examined arthropod lineages, the dominant species during the Cambrian – the purported rapidity of change is still consistent with evolution biology. While there are numerous competing theories regarding what prompted the Cambrian radiation, intelligent design advocates are not presenting a necessary corrective or contribution to the debate, but only more supernatural obfuscation.

Geologist and author Donald Prothero, writing in Skepticblog, explained that the term Cambrian ‘explosion’ is archaic, dating from the beginnings of geology, and a bit misleading. The Cambrian radiation was more of a slow burning fuse, with increasing numbers of fossil types tracing their lineage back to the Ediacaran period, the 94 million-year period preceding the Cambrian.

Let’s all understand geology and the Earth’s natural history – it is an endlessly fascinating and developing subject. However, scriptural reconciliation is not the goal of the natural sciences, no matter how much intelligent design proponents would like it to be. It is advisable keep theological speculations separate from scientific investigations.

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