While we often speak of the “Cambrian Explosion” to describe the main phase of biodiversity 540 million years ago, a new study shows that this event cannot be seen as a violent episode, but on the contrary can be registered as a slow and gradual phase can Diversification spanned more than 100 million years.
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Although life arose very early in the history of the earth (the first living organisms are mentioned around 3.8 billion years ago), it remained at a very primitive stage for a long time – 3.4 billion years to be precise. It wasn’t until about 540 million years ago that the situation changed drastically and life on Earth really took off, leading to unprecedented diversification in the planet’s history. This major stage, which occurs at the beginning of the Cambrian and marks a turning point in the formation and evolution of a great many species, is commonly referred to as the “Cambrian Explosion,” suggesting that it was a fairly violent event.
For a research team, however, this idea would be wrong and would only serve to satisfy our need to limit the evolution of life on Earth through several spectacular and well-defined “grand events” in time. Too simplistic a vision for these scientists, who present their arguments in an article published in the journal Palaeo3.
An explosion that isn’t one
If the fossil archives show that the first animals did in fact experience a very rapid diversification around -541 to -485 million years ago, this fundamental development of living things can by no means be described as an “explosion”. A term that emerged in the 1960s and has since become established in the scientific community and the general public. In the 1990s, another terminology was added, that of the “Great Biodiversification of the Ordovician”, which describes a second stage of the massive diversification of species during the Ordovician, i.e. between -485 and -443 million years. Again, this is an “event” of rather limited duration on the geological time scale.
For Thomas Servais of the University of Lille and his colleagues, these two evolutionary “big bangs” could in fact not be clearly individualized and would simply be part of a single and unique phase of diversification, certainly large, but spanning the long term, from the end of the Precambrian to the end of the Silurian. So this phase would have lasted at least 100 million years. According to their study of this development in biodiversity, no particular “event” stands out during this period.
A bias in the data
This previously prevailing definition would only result from a distortion of the available data. In fact, the databases of paleobiology would be incomplete, especially for the period marking the end of the Cambrian, leading to a fictitious separation of two events that in reality would just belong to the same evolutionary trend. On the contrary, while some groups of fossils have been studied extensively, others have been the subject of little study. The same applies to regions. Thus, these regional studies, or studies focused on a limited number of species, would have given the impression of observing two distinct events. An impression that disappears when you look at the development of biodiversity more globally.
So instead of two peaks of diversification, there would have been just one long and slow evolution spreading out at the beginning of the Paleozoic. To describe this crucial period in the history of life on Earth, scientists propose the use of more measured and less sensationalized terms, particularly the term “radiation” or, quite simply, “biodiversification.”