The 890 million-year-old fossil may be the oldest animal life discovered so far

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More than two decades ago, Elizabeth Turner embarked on a helicopter trip to the Mackenzie Mountains, a vast range tucked away in a remote part of northwest Canada. The mountains provide a window into the ancient past: they contain the geological remains of an ancient reef system built by algae.

Turner, now a professor of geology at Laurentian University in Ontario, says she wanted to understand corals on a microscopic and macroscopic level. “It’s as large as a modern coral reef; kilometers in diameter and hundreds of meters thick,” she notes.

When she first got to the mountains, she said she had “stumbled” – there was a lot of limestone, a type of rock made up of calcium, but it was mostly featureless. “Weathering is completely gray and you can’t see what’s inside,” she notes. So Turner collected a batch of samples, from all over the 890-million-year-old reef (known as Little Dal) and brought them back to the lab for examination, cutting the rocks into incredibly thin slices and looking at them under a microscope.

Among her samples, she discovered something unexpected.

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“Just a handful of specimens, very few specimens, contain this strange, unexpected and intricate thing that says, ‘I really don’t belong here,'” she recalls. “The ‘strange and complicated thing’ was a series of worm-like microscopic structures.” But they didn’t call her Ph.D. And so she put the discovery aside. She thought to herself, “I’ll deal with this later.”

It came much later, as is often the case in academia. Those unusual specimens didn’t gnaw on her, but she knew they were important. She says they didn’t look like microbial structures – they were too complicated for that. And they had a familiar texture that she saw in younger rocks. You may have thought they were related to sponges: porous “basic” animals that have no organs or nervous system, and are considered among the oldest living on Earth.

On Wednesday, in a study published in Nature, Turner made her case for this hypothesis, noting that the microstructures discovered in ancient Little Dal reefs are indeed sponge microfossils, making them about 350 million years older than the oldest animal ever described. .

It’s a big claim — and it’s sure to be debated — but Fritz Neuweiler, a geologist at Laval University in Quebec, who was not involved in the study, called the work a “good step forward,” noting that the paper was “good — grounding, brave and exciting.”

Over 890 million years ago, the Earth was an entirely different place. There was only one giant continent, known as Rodinia. North America was at the center of this huge landmass, with all the other continents trapped around its edges. The Little Dal reef system is set far away, submerged under the shallow waters of the ocean.

Coral reefs were full of life at the time, and were mainly occupied by microbes such as cyanobacteria, or algae, which use the sun to produce energy just like plants. Stromatolites, which are mats of bacteria that can grow up to a meter in length, were also present. Turner says she would have loved to dive over it.

“It would be such a beautiful stromatolite meadow, it would have been blue-green because of the cyanobacteria and it would have been very sticky,” she says.

Elizabeth Turner at work, in the field, on Baffin Island, Nunavut.

C Gilbert.

You wouldn’t be able to see these sponges, even though they were very small. Today’s sponges come in a large variety of colors, shapes, and sizes, but they are mostly made up of “demospongs,” who are true survivors, living through every major extinction event.

In the time of Little Dal reefs, the surfaces exposed to the sun could not be competed with, so it is likely that they existed in the interspaces; Between rocks and crevices, between cavities and possibly on the sides of reefs as well.

Living near cyanobacteria would have been very beneficial for the sponge, Turner says. The cyanobacteria would produce oxygen, which the sponge could use, and “it likely would have provided a food source as well, because the cyanobacteria produce polysaccharides,” she said. Sponges have no mouth or organs, as such, but let food run through the water, in and out of their bodies. Living next to algae was like living next to a buffet and an oxygen factory at the same time. Turner calls it “Nirvana” for the sponge.

As the world changed, coral reefs disappeared, but the potential signs of sponges have not. During the life of sponges, they incorporate crystals of the mineral calcite – calcium carbonate – into their skeletons. Corals were buried over time, but the calcite remained, leaving fossils within the rock for Turner to examine 890 million years ago.

If Turner’s results are confirmed, they can, quite literally, rewrite history.

Turner points to a lot of previous research that other groups have done in the past 10 years, looking at fossils of the Aeozoic sponge body. The Cenozoic Era began about 541 million years ago, near the Cambrian explosion, when animals began to appear everywhere in the fossil record. The most definitive previous fossil evidence for sponges comes from this time, and much work has been done exploring how signs of living things have survived to the present day. “In the past few years, there has been promising work on how to preserve sponges,” she says.

Turner describes it as a slow science. She has been able to base her hypothesis on the background of clear evidence in the literature of younger sponges and believes her explanation is logical. However, it does not put a definitive end to it. “It would be foolish to be overly confident,” Turner says. “I want to acknowledge that what I do is make an informed suggestion.”

Left: Microscopic structures discovered in rocks at the ancient Small Dall Reefs.

Right: Fragment of the skeleton of a modern keratose sponge.

EC Turner

The fact is, scientists have been here with sponges and early life before.

Some evidence suggests that sponges may have originated 800 million years ago, but physical evidence is lacking. A 2016 study claimed to have discovered particles indicating sponges in a 650 million-year-old rock. Further analysis of these particles by a different group of scientists, including Jochen Brooks, a geologist at the Australian National University, suggested that these particles were likely formed by algae and geological forces, not sponges.

This means that Brocks is not unfamiliar with claims of “the oldest animal ever.”

But Brocks isn’t trying to pour cold water on Turner’s ideas – quite the contrary. “I’d like this stuff to be a sponge, because it would be so sexy,” he says. He did, however, mention the case of Namaboykia, an organism known from micro-structures in limestone that was originally thought of as known animal life before later evidence showed that it may actually have been formed by bacteria. This case study shows that science works perfectly, and it’s a good reminder to keep an open mind when it comes to first-ever animals.

“Especially in carbonates, the most amazing and beautiful things of biological appearance can grow just by rearranging and regrowth of crystals,” he notes.

Unfortunately, the Little Dal reef system is somewhat unique, which makes it difficult to find similar microscopic structures from other formations around the world. “There are no other examples of this type of reef in particular,” Turner says. So finding other examples of these microstructures and confirming that they are the body fossils of ancient sponges will take time.

But after two decades of contemplating what these structures were, Turner used to go slow. It may be a good thing that these structures weren’t formed from sponges at all, but something more unusual we haven’t thought of yet.

“We’re dealing with this in-depth time here,” she says. “Maybe there was another species of organism that made a 3D anastomosis network, right? We don’t really know. We’re looking.”

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