An article published in the journal “Nature” reports a study on microfossils with structures similar to those of modern sponges that have an estimated age of about 890 million years, much older than any fossil attributed with certainty to animals. Geologist Elizabeth Turner of Laurentian University, Canada, studied microfossils from an area of northwestern Canada known for Precambrian fossils, part of the Stone Knife Formation. This study has already divided paleontologists due to the difficulty of ruling out that these are fossils of different origin or even false fossils generated by some type of crystallization.
Sponges might be the first animals to emerge in the history of life on Earth although there are still discussions with some researchers who believe that comb jellies emerged earlier. The difficulties in finding fossils that can be attributed with reasonable certainty to sponges or other primitive animals are considerable and discussions are normal.
Elizabeth Turner is now a professor at Laurentian University and has been researching particularly ancient fossils for many years. This means that she looks for interesting rocks, breaks them into fragments, and examines them under a microscope. Years ago, she discovered structures in some of the examined fragments that seemed too complex to be of bacterial origin, but only after years of research did she decide to publish her conclusions.
The structures discovered by Elizabeth Turner resemble those of modern sponges but are estimated to be around 890 million years old. The image (Courtesy Elizabeth C. Turner. All rights reserved) shows 890 million-year-old fossil structures on the left and the “skeleton” of a modern sponge on the right. These fossils are over 300 million years older than the earliest fossils attributed with reasonable certainty to sponges and that immediately sparked discussions with conflicting opinions.
Some genomic research tried to estimate when the first sponges emerged, and that might have happened even a billion years ago. However, there are discussions and controversies on this point as well given that it’s not easy to extrapolate the genetic history of a group of organisms so far back in time.
Among the objections to Elizabeth Turner’s discovery is the lack of geographical spread of those alleged sponges thinking about the fact that animals move and therefore tend to occupy any available niche. If the fossils are really of sponges, they lived in an age when there was less oxygen than today and perhaps they occupied limited niches avoiding harsher environments. 890 million years ago there were colonies of photosynthetic bacteria that produced oxygen that could support the life of more complex organisms that lived close to them.
Other objections concern the possibility that these are structures generated by organisms other than sponges or even by non-biological crystallization processes. The age of these fossils makes it impossible to find traces of biological molecules related to sponges that are present in more recent fossils and detectable by spectroscopic examinations.
Fossils attributed to sponges make up only a small fraction of the ones studied by Elizabeth Turner over the years. The scientist continues her research but they’re long and complex. Probably, the last word on the origin of sponges and animals in general is still far away.
