Life as we know it took a pretty funky turn around 541 million years ago. That’s when a period called the Cambrian emerged, and with it, the so-called Cambrian explosion ushered in practically all major groups of animals. It lasted for about 25 million years and resulted in the divergence of life as we know it.
Before the Cambrian explosion, life on Earth was simple and small. It was composed either of individual cells, or of microscopic, multicellular organisms — or at least so we thought.
Scientists have found some evidence of animal life existing before the Cambrian. In particular, some sponges (immobile aquatic animals) seem to have emerged before the Cambrian. But how long before it?
According to a recent study, the first sponges emerged a whopping 350 million years before the Cambrian — or 890 million years ago.
“If I’m right, animals emerged long, long before the first appearance of traditional animal fossils,” study author Elizabeth Turner told Nature. “That would mean there’s a deep back history of animals that just didn’t get preserved very well.”
The fossils discovered by Turner, from a remote area of northwestern Canada accessible only by helicopter, resemble some modern sponges known as keratose demosponges. The researchers dated the layer of rocks in which the sponge fossils were found, a solid analysis tool that leaves little room for question regarding the fossils’ age. The identification as sponges also seems pretty clear.
“This organic skeleton is very characteristic [of sponge fossils],” explained geobiologist Joachim Reitner, who reviewed Turner’s study ahead of publication. “[T]here are not known comparable structures.”
But a finding that would force us to reconsider the evolution of life on Earth won’t happen easily, and Turner’s peers are rightfully raising all sorts of questions regarding the fossils. Some point out that the findings may not be fossils at all (but rather other structures), while others are focusing on another question: if life emerged a few hundred million years before the Cambrian, why haven’t we found any fossils of it until this?
Ultimately, if the finding is confirmed, it will help us understand the evolution of life on Earth.
“We are animals,” Turner said. “And we have a big brain, and we’re capable of wondering about stuff, and we wonder how we came to be.
“What happened before, and what was it like? How did it begin?” she said. “This is really digging into that. I’m shaking up the apple cart.”