A field site in the Mackenzie Mountains where possible evidence of the oldest animal fossils ever recovered was found. Photo: Elizabeth C Turner
A newly published study proposes sponge-like fossils found in the Mackenzie Mountains may hold the earliest evidence of animal life on Earth.
To a non-geologist, the magnified images of fuzzy, white, worm-like shapes could seem unremarkable. Those patterns may be the fossilized remains of 890-million-year-old sponges according to a paper published on Wednesday.
Elizabeth Turner, a professor of sedimentology and paleontology at Laurentian University, authored the study.
Turner says the first known animal fossils are dated at around 540 million years ago. That makes her discovery potentially 350 million years older than any other recorded animal fossils.
Turner published her findings decades after collecting the first fossil samples during her PhD work.
“I was working on very large microbial reefs. They were made by bacteria, and I was studying them under the microscope,” Turner recalled.
She noticed something unusual in the carbonate rock samples but put it aside for later consideration.
“I encountered, in just a very few samples, this odd thing that did not fit. It was much more complicated than everything else, too complicated,” Turner said.
“I thought I kind-of had an idea of what it was – it looked a lot like younger sponge fossils – but I couldn’t prove it. And it wasn’t the purpose of my PhD anyway. So I had the luxury of putting it aside for later consideration.”
The big picture
Turner says the long gap between her initial sample collections and the published findings makes this “not a normal science story.”
“When I became a professor, I went back and collected a lot more from the same localities so that I had a better collection to work from. But what really brought the study to completion was the publications of others in the last few years,” she said.
“What I really needed was a foundation of other people’s work on how sponges become preserved in the rock records. There came to be a critical mass of that work published by early 2021. So I felt I was willing to go out on a limb with my own material, which was very, very similar, but considerably older.”
Despite the significance of the discovery, Turner said there was no big ah-ha moment.
“I’m not shocked by it,” she said.
“When you think about the big picture – which is the reality that the predictions, the genetic predictions, are that there were sponges back then – this is kind of like a ‘yeah, this is what we expected’ moment.”
In the scheme of a 4.5-billion-year-old planet, the recorded existence of animal life on Earth is still relatively recent and the fossils that have been found are “structurally complicated,” according to Turner.
“There’s a back history during which animals were probably out there but not getting preserved, or at least not getting preserved in a way we’ve recognized yet,” she explained.
“So there’s a huge amount of time and rock that needs to be interrogated to understand, really, the true history of animal evolution.”
Seafloor to mountain range
The rocks Turner interrogated for this study are from the Mackenzie Mountains, a range that straddles the Yukon and NWT border. Turner noted this area would have been the opposite of a great mountain range 890 million years ago.
Turner says if it were possible to travel to that time, “just before you died of suffocation, because there wasn’t enough oxygen in the atmosphere for you to survive, you’d say, ‘Hey, did they send me to a different planet? I don’t recognize any of this.’
“All the continents on Earth were snuggled together in a supercontinent, they were all glued together. And our ancestral North America was in the middle. A lot of the interior of it was flooded with seawater.”
The possible sponges would have come from the reefs in this marine environment, according to Turner.
A geological grey area
Turner plans to elaborate on her research in future papers but says she’s not looking for black-and-white answers.
“The geological record is almost absent,” she said. “Most of Earth history, most of the places and things on Earth that have ever happened, they don’t get recorded, right?”
“I’ve got this little speck of this weird, weird thing that’s hard to understand.
“People seem to think that science is about producing numbers and final answers. And if that’s what you want from science, don’t be a geologist.”