Half a billion years ago, the Grand Canyon teemed with life
Hillel Aron
(CN) — New archeological findings from the Grand Canyon have shed light on what life was like there during the Cambrian period, roughly 500 million years ago, long before the Colorado River cleaved the famous ravine.
What was life like? It was small. But there was quite a lot of it. Researchers have found that the area we now call the Grand Canyon was an evolutionary "Goldilocks zone," the perfect place for tiny organisms to experiment and thrive.
Back then, the area was closer to the equator and sat on the continental shelf, which was much wider than today, because the sea level was much higher. That meant that the location that is now the Grand Canyon was, at the time, flooded with a shallow layer of seawater. The ocean water was not too deep and not too shallow, allowing sunlight to penetrate into the water, which spurred on photosynthesis, releasing oxygen and nutrients.
"We see that reflected in the trace fossil record, because sometimes you come across slabs of rocks which are just completely packed with burrows and feeding traces, which means that there were really high population densities of many of these animals," said Giovanni Mussini, the lead author of a paper published Wednesday in the journal Science Advances. Mussini is a doctoral student at Magdalene College at the University of Cambridge in England.
In 2023, Mussini went on a paleontology expedition along the Colorado River and through the Grand Canyon, where 1.5 billion years are displayed in multicolored stripes — a veritable layer cake of geologic and biologic history. Mussini focused his digging on the Cambrian period, which occurred roughly between 541 million and 485 million years ago.
"It's really the time period where all the foundations of the of the animal dominated biosphere came about," Mussini said. "We're talking about the really major groupings, like vertebrates, mollusks, annelid worms and arthropods. And so the basic body architectures that we see in the animal kingdom today, they come online during the Cambrian."
He brought back just over 30 fist-sized rocks, samples that were then studied under a microscope. He found fossils in two of the rocks.
"Sometimes you get lucky," Mussini said.
Among the trove were tiny fragments — millimeters in size — of rock-scraping mollusks and filter-feeding crustaceans. He found traces of burrowing, walking and even fragments of the food the animals likely ate. A picture began to come into focus of life back then. He even discovered a new species.
Most animal fossils from the Cambrian are from hard-shell creatures, including plenty of trilobites. But Mussini's find included a rarely spotted soft-bodied creature — a spiky-toothed worm, perhaps 10 centimeters long. This newly discovered species of priapulid, sometimes called a "penis worm" or cactus worm, had hundreds of complex branching teeth. It reminded Mussini and one of his fellow researchers of the Krayt dragon, a fictional animal that has appeared in Star Wars video games and TV shows. And so the new worm was christened Kraytdraco spectatu.
"Both creatures — both the fictional one and the Cambrian one — they both come from, from a canyon of sorts," Mussini said. "They're worm-like and full of teeth, so we thought, this is a done deal."
The findings give a fuller picture of the Cambrian period, when evolution was beginning to ramp up, and life was becoming more complex.
"The fact that this environment was so habitable and full of resources means that the main source of adaptive innovation were other organisms," Mussini said. "Because when you have a plentiful base of resources, when you can afford to invest in pretty much whatever you want, physiologically speaking, the main constraint on your evolutionary success is going to be how well you can keep up with the competition, or how well you can negotiate interactions with other organisms. What really introduces a premium for the evolution of complexity are other organisms.
"So the tale, I would say, is one of life begetting more life."