Approximately 520 million years ago, various animals exploded onto the evolutionary scene in the Cambrian explosion, an event that pushed marine animals to evolve some of the basic body forms that are still present in modern groups over the course of 10 million years. However, while some paleontologists view this event as a real example of amazing evolution, others claim that it is simply a false remnant of an unreliable fossil record. Now, scientists from the University of St. Andrews claim to have unlocked the secret behind this event, pointing to the geography of Cambrian Earth as the unifying factor for these two theories.
"In a nutshell both camps were right. The particular locations of Cambrian continents relative to each other was special in a way that supercharged animal speciation while preserving an unusually good record of those early fossils," Timothy Raub, co-author of the paper, said in a press release.
The mystery is what is known as a "true polar wander," which takes place when the entire solid Earth slips about its liquid outer core over the course of millions of years. This process is contrary to the standard processes of Earth's continental and oceanic plates that are typically in constant motion relative to one another and can cause the geographic locations of Earth's plates to shift altogether in the same directions.
The team suggests that approximately 520 millions years ago, a giant lurch of more than 60 degrees led to the shifting of most continents from polar to tropical latitudes. This early Cambrian rotation led to an increase in the shallow coastal area near the equator, the area of the Earth where biodiversity it at its peak for reasons that are still debated.
Furthermore, the team also suggests that this true polar wander caused these continents, moving toward the equator, to be flooded with sea level rise due to their exposure to the bulge of water caused by the Earth's daily spin, which in turn increased fossil preservation and prompted the rapid diversification of habitats.
"A bunch of wonderful ideas have been published emphasizing one or another aspect of the Cambrian biosphere as the crucial link in the explosion of animal life," said Raub. "An appealing aspect of our study is that a geographic contingency - the shape and arrangement of the Cambrian continents and the direction of the remarkable true polar wander shift - can support almost all those ideas simultaneously. At the same time, it turns out that preservation of Cambrian fossils really was enhanced over that of other ages."
"This new geographic framework answers a debate going back over a hundred years," he concluded. "It should encourage scientists to review all sorts of old and new hypotheses, which no longer must fit into the evolution or preservation camp exclusively."
The findings were published in the December issue of the American Journal of Science.
