New research suggests that the Cambrian explosion, which saw an upsurge in animal life some 520 million years ago, resulted from a combination of interlinked factors rather than one underlying cause. The study's findings are published in the latest edition of the journal Science.
Over the past few decades, many individual theories have been put forward to explain this rapid diversification of species. But a paper from authors Paul Smith of Oxford University and David Harper of Durham University suggests that a more holistic approach is needed.
Current theories that seek to explain the Cambrian Explosion can be categorized into three main groups – geological, geochemical and biological. Most of these theories are claimed as standalone processes, that is, they were the main cause of the explosion.
Whatever the source, the evolutionary event produced a wide range of biological innovation, including the origin of modern ecosystems, rapid increases in animal diversity, and the first appearance of such specialist modes of life as burrowing and swimming. Vertebrate animals, which are the distant ancestors of modern fish, reptiles, birds and mammals, also appeared in the Cambrian Explosion.
A team of scientists led by Smith and Harper have spent the last four years working on data from a site in northern Greenland. Located at Siriuspasset, the site is just 500 miles from the North Pole. While difficult to reach logistically, the team was attracted to Siriuspasset because of its high quality fossil material and the insights this could provide.
The researchers describe the interacting causes behind the explosion as a "cascade of events," in which animal life likely began with sea level rise in the early Cambrian. With rising sea levels there would have been an increase in the area of habitable seafloor, which in turn could drive an increase in animal diversity. These early events encompass the complex interaction of biological, geochemical and geological processes described individually in previous hypotheses.
Referred to as one of the most important events in the history of life on Earth, it would be naïve to think that any one cause was behind the explosion of animal life. It's far more likely that a chain reaction, which involved a number of biological and geological drivers, escalated the planet's diversity within a relatively short period of time.
Most of the previous hypotheses have contained some kernel of truth, but each, in isolation, has been insufficient in explaining the cause of the Cambrian explosion. Future research should focus on the sequence of interconnected events that occurred and the way they related to each other.
