Animals might have been there a whole bunch of tens of millions of years sooner than beforehand thought
According to the most popular theories, evolutionary biologists claim that life on earth began about 4 billion years ago, beginning with unicellular bacteria and gradually giving way to more complex organisms. The first complex organisms in the form of fungi, algae, cyanobacteria and sponges emerged according to the same evolutionary schedule during the Neoproterozoic (around 800 million years ago).
However, based on recent findings on the Arctic Circle, it appears that sponges existed in the Earth’s oceans hundreds of millions of years earlier than we thought! These results were made by Prof. Elizabeth Turner of Laurentian University, who excavated the fossilized remains of 890 million year old sponges. If confirmed, these samples would be about 350 million years older than the oldest fossilized sponges.
Elizabeth Turner is Professor of Invertebrate Carbonate Sedimentology and Paleontology at the Harquail School of Earth Sciences at Laurentian University in Sudbury, Ontario. She is also a field geologist with 30 years of experience in Canada’s Northwest Territories specializing in the dynamics of carbonate and shale basins from the Proterozoic and Paleozoic Era. The study describing their research appeared in the July 28 issue of the journal Nature.
This is the skeleton of a modern bath sponge or horn sponge from Greece under a microscope, which has a similar structure to the fossils. Photo credit: Elizabeth Turner / Laurentian University
In summary, sponges are simple forms of life and one of the earliest forms of multicellular life. Genetic evidence from modern sponges suggested that the first sponges formed during the Neoproterozoic (about 1,000 to 541 million years ago), but fossilized remains from that period were missing. Turner discovered these fossils while doing fieldwork in the Mackenzie Mountain Range in Canada’s Northwest Territories as part of her PhD.
While this region, which borders on the neighboring territory of the Yukon, is now part of the Arctic Circle, it was 890 million years ago in a shallow inland sea in the middle of the supercontinent Rodinia – so much closer to the equator. Turner found these fossilized remains while researching limestone reef pockets and crevices that form in the presence of photosynthetic microbes known as cyanobacteria (also known as stromatolites).
These fossilized remains were worm-like in appearance and were likely formed in the presence of calcium carbonate-depositing bacteria, as evidenced by the networks of tubular structures and the presence of calcite crystals in and around them. These structures closely resemble the fibrous skeletons observed with the modern horn sponge, as well as structures in carbonate rocks that are attributed to the decay of these animals.
“They are really identical to the ones I had in my much older rocks,” Turner said in a recent interview with the CBC. “There weren’t any other really workable interpretations of the material.” The limestone deposits Turner found them also resemble the environments sponges live in today. Prof. Turner suspects that the structures could be the fossilized remains of horn sponges that lived between calcium carbonate reefs 890 million years ago.
These microscopic 890 million year old fossils found in the Northwest Territories are believed to be the remains of an ancient sponge. If that were the case, they would be by far the oldest animal fossils ever found. Photo credit: Elizabeth Turner / Laurentian University
Turner puzzled over these samples for decades and regularly returned to the Mackenzie Mountains to collect more samples. Then, between 2014 and 2021, researchers in Germany, the United States, and Korea published research showing how similar fossils might have formed from horn sponges. This led Turner to conclude that the worm-like fossils may not have formed in the presence of microbes, but were the result of sponges that existed 890 million years ago.
These results suggest that the evolution of early animals may have occurred independently of the “Great Oxygen Event,” which began about 2.4 to 2 billion years ago when photosynthesis metabolized atmospheric carbon dioxide and produced molecular oxygen. For the next billion years, much of this oxygen was taken up by the oceans and the earth’s crust, but by about 800 million years ago the oxygen levels are believed to have reached the point where they could support animal life.
Should these structures turn out to be fossilized remains of ancient sponges, this could mean that the evolution of the early animals occurred independently of this oxygenation event. Additionally, the reef pockets and crevices where they were found were too dark for photosynthetic cyanobacteria, so there was likely no competition between the sponges and other microbes.
However, they could still have been so close together that the sponges would have been able to take in some of the oxygen produced by the cyanobacteria (which was in short supply at the time). It would also mean that early animal life survived severe ice ages that occurred 720 to 635 million years ago – during the cryogenic era. All previously discovered samples are from periods that came after this geological period.
This is one of the sites in the Mackenzie Mountains of the Northwest Territories. The mountains contain limestone from huge ancient reefs where the fossils were found. Photo credit: Elizabeth Turner / Laurentian University
These include the 574 million year old fossils discovered in the Mistaken Point Ecological Reserve on Newfoundland and the leaf-like marine animal called Dickinsonia, which is approximately 558 million years old. Since its publication, Turner’s study has been peer reviewed and several scholars have publicly endorsed its results – which is unusual as the peer review process is usually anonymous.
Other researchers remain skeptical, such as Jonathan Antcliffe, a paleontologist at the University of Lausanne (UNIL) in Switzerland, who has denied earlier claims about “oldest sponges”. There is also Qing Tang, a postdoctoral fellow at the University of Hong Kong, who compared these results to fossils dated to 635 million and 538 million years ago. Again, these fossils were believed to be the remains of sponges, but were later created by microbes. As Qing told the CBC:
“Overall, this discovery is very interesting. It will be a big step towards a better understanding of early animal evolution when the keratotic sponge interpretation is finally confirmed, especially given its age … However, as indicated in the title, these structures are best known as possible sponge fossils because of the relatively few features they conserve . “
Obviously, more testing will be needed to validate Turner’s conclusions and more samples from the region will likely be needed for comparison. As always, the reconstruction of the earth’s history and biological evolution is arduous. But with each new discovery, the secrets of how life began and evolved on our planet are slowly being revealed. This constant pursuit also helps in our search for life elsewhere in the solar system and (ultimately) in the universe.
Further reading: CBC, Natur