An article published in the journal “Science Advances” reports the results of a thorough examination of a rock dated between 3.75 and 4.25 billion years offering evidence of the presence of microfossils. A team of researchers discovered in a rock found in the Nuvvuagittuq Greenstone Belt, Quebec, fossilized structures that bear similarities to microfossils from a later era and to today’s bacteria living in hydrothermal vents. This discovery offers new evidence that at the time, there were already diversified life forms after the evidence published in an article in the journal “Nature” in March 2017. In that case, the nature of the structures sparked controversy but the ones presented in the new study have greater complexity.
Identifying and examining fossils of primitive life forms is difficult for a variety of reasons. The scarcity of fossils dating back over three billion years and their microscopic size make them difficult to find. The similarities between microfossils of primordial life forms and structures generated by non-biological processes make it difficult to identify with certainty the remains of microorganisms.
In the so-called Nuvvuagittuq Greenstone Belt in Quebec, Canada, there are very ancient rocks though their dating, made using different methods, is approximate. The different techniques provided ages between 3.7 and 4.32 billion years. These rocks were on a primeval seabed with hydrothermal vents of the type where the first life forms may have emerged. This made rock studies in that area interesting but the results were the subject of controversy.
Iron oxidation may have been at the center of an important type of metabolism among early life forms. For this reason, their possible chemical traces are the focus of research in this field. The researchers who conducted the study published in “Nature” in March 2017 believed they had discovered microfossils of primitive life forms but those results were disputed by some colleagues, who instead believed that those are structures created by non-biological chemical reactions.
Some of the researchers continued examining the rock with other colleagues and found other more complex structures. These are tubular structures with various branches and distorted groups of spheres. Spheroidal structures and tubular structures made of the iron oxide type called hematite are commonly associated with fossils and today’s iron-oxidizing bacteria.
In part, these are structures like the ones already described in the study published in 2017 but some have more complex shapes, compared to trees due to their ramifications. According to the authors of the new study, the probabilities that these are structures of biological origin are very high, also because such structures have never been seen produced by non-biological chemical reactions.
In essence, the researchers confirm the conclusions of the 2017 study and bring new evidence to their thesis. The time elapsed between the two studies shows the complexity of examining microfossils and mineral deposits generated by non-biological processes. The controversies accompanying these studies require offering as much evidence as possible to the conclusions.
Dr. Dominic Papineau of University College London, lead author of the new study and part of the team that conducted the study published in 2017, pointed out that the findings strongly suggest that between 3.75 and 4.28 billion years ago a diversity of bacteria existed on Earth. This means that life may have begun as early as 300 million years after the Earth’s formation.
Doubts may still remain after this new study, and it’s important that discussions continue to improve methods for distinguishing microfossils from non-biological process products with reasonable certainty. These are important advances to reconstruct the early stages of the evolution of life on Earth with consequences also in the search for life on other planets. For example, if life indeed emerged so quickly on Earth, there are more chances that it also emerged on Mars, where conditions were similar at the time.
