Earth’s deep oceans 500-million years ago, believed by some to be inhospitable to life at the time, were actually conducive to it, a new study suggests.
Back then, the planet looked quite different. Rising seas inundated huge supercontinents that would become the land masses we know today, making way for an explosion of new, complex lifeforms; a hallmark of this vibrant era called the Cambrian period.
During Cambrian times, in what are now the Mackenzie Mountains of Canada’s far north, a muddy ecosystem teemed with worms, crustaceans, and other ancient organisms. Some tunneled vast avenues beneath the seabed, forming a “superhighway” of tiny burrows. Others, earthworm-like predatory species, lurked in shallow vertical holes, waiting to snatch unsuspecting prey.
A snapshot of these moments was exquisitely preserved in the fossil record, to be stumbled upon millennia later by Brian Pratt, a geologist at the University of Saskatchewan who has studied this prehistoric environment for 25 years.
The discovery happened “years ago” on an expedition to the Mackenzie Mountains, Pratt told Motherboard on the phone.
“The sun came out, and I took a walk just down the valley where I hadn’t been, and saw this peculiar green rock,” Pratt recalled. “And I said, ‘Jeez, there are fossils of soft-bodied animals in it.’”
Pratt excised slivers of the shale rock and transported them to the lab. After dressing them with alcohol (“because that changes the contrast a little bit,” Pratt explained) he carefully placed the samples onto a flatbed scanner for imaging.
Then, in Photoshop, Pratt cranked up the illumination and contrast. “I couldn’t believe it,” he said, describing what he saw.
Some of the fossils were immediately identifiable as coprolites, or fossilized poop. They likely belonged to a predatory, “pretty substantial worm,” (up to 1.5 centimeters in diameter) that lived in holes beneath ground and hunted crustaceans and other organisms, Pratt said. It was was described in a paper that he and then-PhD student Julien Kimmig published to Palaios last year.
The duo also found fossilized evidence of worm tunnels, some only a millimeter in size and others the width of a finger. These burrows penetrated almost every layer that was sampled, according to the new study.
The team’s findings were published in this month’s edition of Geology.
Immaculately preserved fossils, such as the famous Burgess Shale in the Canadian Rockies—a robust cross-section of an entire ecosystem—are believed by some to exist because of low oxygen conditions near the seafloor that halted decay.
So the discovery of a once thriving ecosystem here, demonstrating that some life did exist, warrants further research as “something [being] behind the preservation,” Pratt said.
“If you don’t see the evidence for animals living in the sediment, you assume they weren’t there,” he added.
One possible explanation is that clay minerals in the seabed interacted with the organic matter and stopped the decay.
In the meantime, Pratt is eager to analyze other shale deposits for evidence of life. “Maybe we’ll try to collaborate with some colleagues,” Pratt suggested. “And they’ll say, ‘Hey, why don’t you work your magic on these.’”
“The personal part, is the thrill of discovery,” Pratt said.