Imagine for a second the first animals to appear on our planet. Most likely, your imagination conjures the image of the so-called Cambrian explosion, which was a mysterious period in prehistory populated by bizarre-looking trilobites, armoured marine animals, and even more bizarre predators swimming in the primaeval seas. Indeed, school books have been telling us for many years that this marked the definitive beginning of animal evolution. But high above the rough terrains of northwestern Canada, a bunch of minuscule squiggles found inside fossilised reef rocks may prove otherwise.The tiny patterns are so small that you can literally walk past them without even noticing them. However, they have led to an enormous scientific controversy that might make the date of origin of animals shift by as much as 350 million years back. In case all these discoveries turn out to be true, then it will mean that animal life had been thriving here on Earth millions of years ago, when the present continental configuration had yet to emerge.The microscopic ghost in the reefIt all started when scientists analysed rock samples collected from 890-million-year-old microbial reefs in Canada. These reefs were formed by gigantic bacterial colonies, well before the existence of modern coral reefs. But when scientists studied thin sections under the microscope, they found no traces of usual animal remains such as bones, teeth or shells. Instead, they found something quite recognisable – complex web-like structures.This is because, in their study Possible poriferan body fossils in early Neoproterozoic microbial reefs, which appeared in the journal Nature, scientists made an amazing claim. According to the researchers, the microscopic organisms are a perfect fit for the physical skeletons of today’s keratose sponges. This is because, being one of the most primitive living things on the tree of life, sponges are believed to be the ancestors of the animal kingdom. In this case, if the tiny organisms turn out to be fossilised sponges, then they are the oldest body fossils of animals known to date.The context in which the shapes were discovered makes their tale even more compelling. The potential fossils in question were not deposited on an ordinary seafloor full of life but were entirely contained within ancient bacterial colonies. Rather than being replaced by animals, it seems that the first animals coexisted with bacteria, finding a precarious niche for themselves in low-oxygen oceans.
These structures, resembling the skeletons of modern sponges, challenge the traditional view of the Cambrian explosion as the definitive start of animal evolution, suggesting early animals coexisted with bacteria in low-oxygen environments.
When geology imitates biologyExtraordinary as the discovery may seem, it has left the scientific community completely divided. The crux of the issue is that when you look back into deep time, almost a billion years ago, the distinction between organic biology and common geology becomes very hard to make. Nature is a wonderful artist, and under certain environmental stresses, it is not difficult to shape common rocks into organic forms.This scepticism is a major focus of an analysis published in the Nature journal titled Sponge-like fossil could be Earth’s earliest known animal. Many palaeontologists are urging caution, pointing out that rock-forming processes can create deceptive look-alike textures under the right conditions. Because soft-bodied creatures like sponges do not possess hard shells, they rarely leave a clean footprint in the geological record. Deciphering whether these Canadian rock patterns are genuine animal remains or just a clever trick played by minerals, is a massive challenge.What this discovery does pull off beautifully is bridging the gap between two different fields of science. For years, geneticists tracking evolution through “molecular clocks” have argued that animals must have emerged around 900 million years ago, but palaeontologists could never find the physical fossils to prove it. These tiny Canadian squiggles land exactly in that missing time frame.Whatever happens to be the final say on whether they qualify as actual fossils or just an illusion of nature’s work, what is certain is that they have succeeded in changing our outlook. They teach us that history was not created by the huge bones of dinosaurs, but rather by the invisible marks left in stones. The rocks in Canada have taught us that the truth about our beginnings can actually be found right under our feet.
