New study reveals cause of Earth’s first mass extinction on life

EARTH’S first mass extinction did not unfold in the way you think. Scientists believe they’ve busted a popular myth about the event’s cause.

Earth and asteroid colliding (Elements of this image furnished by NASA- earthmap for render from http://visibleearth.nasa.gov)

IT was Earth’s first known mass extinction of life, but now science may have busted a popular myth about what actually caused it.

A catastrophic meteor strike or the eruption of a supervolcano?

Nope, the planet’s earliest lifeforms were wiped out en masse — by being eaten and trampled to death.

A new study claims the strange tube-like organisms, known as Ediacarans, were made extinct by the emergence of bigger animals that could move.

In a paper published in biological research journal, Proceedings of the Royal Society B, palaeontologists argue the first mass extinction was caused by the arrival of the next species, some 38 million years later, rather than a catastrophic event.

Experts believe Ediacarans existed 579 million years ago. But because they had no shell or vertebrae, the only remnants of their existence are fossilised impressions left in sandstone.

They weren’t mobile, they thrived on the sea floor and were thought to have existed for 37 million years.

The report’s lead author, Simon Darroch, from the Smithsonian Institution in Washington DC, argued the Ediacaran demise began at the start of the Cambrian period (the arrival of the first forms of animals) 541 million years ago.

“These new species were ‘ecological engineers’ who changed the environment in ways that made it more and more difficult for the Ediacarans to survive,” Mr Darroch wrote.

And this is what they looked like ... Parvancorina fossil of animal that lived in the late Ediacaran sea floor found in the Flinders Ranges in SA and the White Sea area in Russia.

The paper then goes on to argue it was changes introduced by those animals that eventually caused many lifeforms to die out.

Their theory is based on the discovery of new fossils at Farm Swartpunt in Namibia, one

of four major sites where Ediacaran fossils have been found. The other major sites were located in South Australia, Newfoundland and Russia.

The fossils they discovered date from 545 million years ago, 1-2 million years before the end of the Ediacaran, IFLScience reported.

A vast number of trace fossils from Cambrian animals were also found showing they had already evolved and were breaking up sediment and disturbing the Ediacaran environment.

“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,.” Mr Darroch says.

The authors argue that animals had an enormous advantage over Ediacarans: they could move. And they believe this enabled them to literally eat the opposition, wiping out all those species that did not adapt in one way or another to this new threat, IFLScience reported.

“There is a powerful analogy between the Earth’s first mass extinction and what is happening today,” Mr Darroch adds. “The end-Ediacaran extinction shows that the evolution of new behaviours can fundamentally change the entire planet, and we are the most powerful ‘ecosystem engineers’ ever known.”

But Australian paleantologist Jim Gehling, from the South Australian Museum, disagrees with the final conclusion, arguing the authors of the paper only studied one of the major sites.

“Basically they conclude they (Ediacarans) have been whittled out by the time of the Cambrian,” he told news.com.au. “I have been to all these sites and they basically only studied one of these sites and that is one of my criticisms of the paper.

“That place at Swartpunt in southern Namibia, while it’s spectacular with a really good exposure, it represents what you call a fairly limited range of sedimentary layers.”

Dr Gehling explained the authors of the paper argued they found trace fossils more complex than ones previously found, but he says his own team have found complex fossils at the Nilpena site in the Flinders Ranges.

Palaeontologist Dr Jim Gehling with Ediacaran fossils that are on display at the SA Museum.

“We are actually in a position to walk from one moment in time to another and look at the diversity as we go through those bits and what we find is there is great variations depending on which layers you are in. So ten metres down the pile you get quite a different assemblage of fossils from those ten metres up,” he said. “My colleague and our teams have been working on this for over ten years.”

Dr Gehling said he believed you can’t make statements about the evolution of life in the ocean in the Ediacaran unless every site had been considered.

“And we have a long way to go to before we can really figure that out,” he added.

“So the place this team did their work while it is spectacular site I would say it represents nothing like the environment we do a lot of work in Australia.

“For all we know you could go to another place in Namibia which is about the same level and get quite different fossils. Namibia is an enormous place. The layers are all flat lying and no one has even looked at all of the rocks in such a remote place.

“And it’s the same problem in South Australia. We have enormous areas which we could explore and we have only just scratched the surface.

“My big problem with this study is that it that it proposes that life got wiped out at the end of the Ediacaran and started again. And I would have to say that is gross simplication because in South Australia, in Namibia, and in Newfoundland, there are many different layers. In newfoundland when you walk across the boundary there are volcanic layers and rocks where there are burrows of all different kinds.

“Whatever was there was quite sophisticated, they had two sets of appendages, they weren’t created five minutes before the Ediacarans died. They were the descendants of the things living before in the Ediacaran. Which things gave rise to the animals that inherited the earth in the Cambrian? That’s really what we are very interested in.”

Pteridinium: One of the common fossils found at Swartpunt that was also found at Nilpena, in the Flinders Ranges, SA.