Antarctica: Geologists discover ‘extraordinary’ fossils
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Early in the Earth’s history, oceans and seas were relatively low in oxygen. A huge pulse of the gas, around 800 million to 540 million years ago, brought atmospheric oxygen levels somewhere within 10 and 50 percent of current levels. Known as the Neoproterozic Oxidation Event, it saw a dramatic rise in oxygen levels in both the atmosphere and oceans.
With a much similar structure to the modern bath sponge, they were found in the “Little Dal” limestones in northwest Canada.
Sponges are the most basic animal type, wrote Elizabeth Turner in Nature.
They are part of the animal kingdom despite lacking the nervous, digestive and circulatory systems typically associated with animals.
It is their carnivorous nature, ability to reproduce and requirement of oxygen to survive that sees them fall under ‘animal’.
The discoveries would be the oldest animal fossils ever if confirmed. (Stock image) (Image: GETTY)
The animals are thought to have been able to survive on minimal oxygen. (Image: GETTY)
Ms Turner first discovered the network of tubes in 1992, but moved on, citing a lack of evidence to conclude they were sponges besides some general resemblance.
She said: “I found this thing that was totally out of place. It was much more complex in terms of its structure than anything that could be made by cyanobacteria.”
Clues over their identity began to build up in more recent years, with researchers finding very similar structures in rocks much younger than the Little Dal reef.
This enabled Ms Turner to present her own findings.
She added: “The accumulation of a critical mass of the papers that provided me, as of now, with a sufficient foundation to present my own works, which is comparable, but in rocks that are much older.”
They were discovered in Canada’s Mackenzie Mountains. (Image: GETTY)
Ms Turner’s discovery “gives good evidence that there were sponges living 890 million years ago”, said geologist Robert Riding.
If her findings are confirmed as sponges, Mr Riding said: “They would be not just the oldest sponges, they would be the oldest animals.”
The oldest dated fossils of sponges, until now, are about 635 million years old.
However some researchers have refused to accept their animal identity.
These fossils would pre-date that by 250 million years.
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Questions have been raised over the findings. (Image: GETTY)
The findings of other researchers which prompted Ms Turner to publish hers suggested the mesh structures could be fossil remains of a group called keratosan sponges.
Her findings lack spicules, tiny rigid structures through which sponges build their skeletons.
Ms Turner argued keratosan sponges also lack spicules, and explained how the colony could have survived.
She pointed to “oxygen oases” which may have enabled these sponges to thrive.
Their structure bares a similar resemblance to modern bath sponges. (Image: GETTY)
Cyanobacteria, which made up the Little Dal reef, are photosynthesising organisms that produce oxygen, thus could have provided enough for the nearby sponges.
By placing paper-thin pieces of the rocks under a microscope, Ms Turner could label the similarities of her findings to keratosan sponges, and to modern sponges too.
She said: “It’s an ode to slow science.”
She admitted there will be sceptics, with Rachel Wood from the University of Edinburgh one of a number of geologists and paleobiologists to raise caution.
Ms Wood said: “She may be right. But I think you really have to explore and disprove all the other possibilities to make such a really strong claim like this.
“I don’t think that she’s really nailed that these are sponges.”
As with all groundbreaking discoveries such as Ms Turner’s, confirmation will be needed from further research, something she is well aware of.
She finished: “We need to be looking for similar material with a really open mind in rocks of similar age, and we need to be looking for more complex animal evidence in them as well.”