The explosion of animal life on Earth took place 520 million years ago as a result of a combination of interlinked factors, and not due to a single underlying cause, according to a new study published in Science.
Although many individual theories have been presented over the past few decades to understand the rapid diversification of animal species in the early Cambrian Period, the new study jointly conducted by Durham and Oxford universities, suggests that a more historical approach is needed to uncover mysteries behind evolution’s big bang that came to be known as the Cambrian Explosion.
“The Cambrian Explosion is one of the most important events in the history of life on our planet, establishing animals as the most visible part of the planet’s marine ecosystems,” David Harper, of Durham University and a co-author of the study, said in a statement.
“It would be naïve to think that any one cause ignited this phenomenal explosion of animal life. Rather, a chain reaction involving a number of biological and geological drivers kicked into gear, escalating the planet’s diversity during a relatively short interval of deep time.”
The researchers have described the factors as a “cascade of events” that are likely to have begun with a rise in sea levels in the early Cambrian period, resulting in a large increase in the area of habitable sea floor, which in turn drove an increase in animal diversity.
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According to the researchers, this major evolutionary event eventually led to a wide range of biological innovations, such as the origin of modern ecosystems, a rapid increase in animal diversity, the origin of skeletons and the first appearance of specialist modes of life such as burrowing and swimming.
“The Cambrian Explosion set the scene for much of the subsequent marine life that built on cascading and nested feedback loops, linking the organisms and their environment, that first developed some 520 million years ago,” Harper said.
The study also reveals facts about a creature to emerge from the early Cambrian -- the Anomalocaris -- a free-swimming predator of the time with a mouth composed of 32 overlapping plates, which could tighten to crush its prey. The creature is distantly related to modern arthropods such as crabs and lobsters.
“This is a period of time that has attracted a lot of attention because it is when animals appear very abruptly in the fossil record, and in great diversity. Out of this event came nearly all of the major groups of animals that we recognize today,” Paul Smith of Oxford University, the study's lead author, said in the statement.
Smith, Harper and a team of scientists spent four years working on data from a site in northernmost Greenland's Arctic coast. The site, at Siriuspasset, is located at 83°N, and is only 500 miles from the North Pole.
Although logistically very difficult to reach, Siriuspasset attracted the team because of the high quality of its fossil material and the insights it provided the researchers.
“What we need to do now is focus on the sequence of interconnected events and the way they related to each other – the initial geological triggers that led to the geochemical effects, followed by a range of biological processes,” Smith said.