Animals, not meteors, were responsible for first mass extinction

The end-Ediacaran extinction shows that the evolution of new behaviors can fundamentally change the entire planet, and we are the most powerful 'ecosystem engineers' ever known.

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Fossil of frond-like Ediacaran species found in Namibia. Credit: Sarah Tweedt, Smithsonian Institution

A commonly held notion that mass extinction on Earth are a result of regular impacts of meteors from Space has been challenged by a new research that claims that animals are responsible for first mass extinction on Earth.

For nearly 3 billion years life on planet Earth was simple – single celled organisms ruled the world – and life was much less complicated. However, things began to change as some organisms started evolving and garnered capabilities through which they were able to capture energy from sunlight. This gave rise to the photosynthetic process.

Despite the fact that photosynthesis is one of the most important evolution in the history of our planet, it did have one polluting effect – creation of oxygen. Organisms at the time were not accustomed to living in oxygen rich atmosphere, researchers at Vanderbilt University explain. So as more and more organisms developed ability to carry out photosynthesis, more and more oxygen was pumped into the atmosphere.

This is the first example of ‘ecological engineering’ that brought about huge changes in the makeup of our atmosphere making it conducive for more complex life forms to evolve, but also making it difficult for the simpletons.

Oxygen allowed growth of multicelluar organisms and thus came the era of Ediacarans some 600 million years ago during a warm period following a long interval of extensive glaciation. These species rule the Earth for millions of years and though they haven’t left behind much clues about their body structures as they didn’t have any shells or skeletons, researchers do know that they managed to spread globally.

Ediacaran fossil found in the Swartput Farm site. Credit: Sarah Tweedt / Smithsonian Institution
Ediacaran fossil found in the Swartput Farm site. Credit: Sarah Tweedt / Smithsonian Institution
Largely immobile and even spending their entire lifetime anchored at one place, the Ediacarans are believed to be largely shaped like discs and tubes, fronds and quilted mattresses. Many fed by absorbing chemicals from the water through their outer membranes, rather than actively gathering nutrients. 60 million years into their reign, things went wild and then came the Cambrian explosion.

During this 25-million-year period, almost all modern animal families – vertebrates, molluscs, arthropods, annelids, sponges and jellyfish – came into being and these species became ‘ecological engineers’ who changed the environment in ways that made it more and more difficult for the Ediacarans to survive explains Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University.

This was the second time that organisms became ‘ecological engineers’ making life simple for themselves and hard for the primitive lifeforms so much so that they eventually wiped out the Ediacarans.

Darroch and his colleagues performed an extensive paleoecological and geochemical analysis of the youngest known Ediacaran community exposed in hillside strata in southern Namibia. The site, called Farm Swartpunt, is dated at 545 million years ago, in the waning one to two million years of the Ediacaran reign.

“We found that the diversity of species at this site was much lower, and there was evidence of greater ecological stress, than at comparable sites that are 10 million to 15 million years older,” Darroch reported. Rocks of this age also preserve an increasing diversity of burrows and tracks made by the earliest complex animals, presenting a plausible link between their evolution and extinction of the Ediacarans.

The older sites were Mistaken Point in Newfoundland, dating from 579 to 565 million years ago; Nilpena in South Australia, dating from 555 to 550 million years ago; and the White Sea in Russia, dating also from 555 to 550 million years ago million years ago.

Darroch and his colleagues made extensive efforts to ensure that the differences they recorded were not due to some external factor.

For example, they ruled out the possibility that the Swartpunt site might have been lacking in some vital nutrients by closely comparing the geochemistry of the sites.

It is a basic maxim in paleontology that the more effort that is made in investigating a given site, the greater the diversity of fossils that will be found there. So the researchers used statistical methods to compensate for the variation in the differences in the amount of effort that had been spent studying the different sites.

Having ruled out any extraneous factors, Darroch and his collaborators concluded that “this study provides the first quantitative palaeoecological evidence to suggest that evolutionary innovation, ecosystem engineering and biological interactions may have ultimately caused the first mass extinction of complex life.”