3.75-billion-year-old tree-like organism suggests life branched out earlier than expected

From microscopic bacteria and beautiful flowering trees to colonies of insects and massive whales, life is abundant on our planet. There are millions of different species in every corner of our world. When did the barren rock that was Earth become such a rich hive of organic activity? New research suggests that the diversity of life we see today may have begun much earlier than previously thought.

Earth is around 4.6 billion years old. Its early days were volatile: peppered with asteroids and experiencing extreme atmospheric and geological changes. Once things settled, the “primordial soup” of chemicals left behind saw the beginnings of life with the appearance of the first single-celled organisms. New fossil discoveries suggest that these organisms began branching out into different species much sooner than expected – maybe as early as 300 million years after the Earth was formed.

While that seems a long time (and, don’t get me wrong, it is), it is a relatively short span in geological terms and comes as a surprise to many scientists.

More on early life on Earth: Rethinking the origins of complex life

A study published in Science Advances looked at a rock from Québec, Canada, estimated to be between 3.75 and 4.28 billion years old. The fist-sized rock contains microscopic filaments, knobs and tubes postulated in an earlier Nature article to have been made by bacteria, predating the previously accepted first signs of ancient life by 300 million years. But some scientists were unconvinced that these structures were biological.

The Science Advances article lays out new findings borne out of further analysis. Included in it is a description of a larger, more complex structure – a stem with parallel branches measuring nearly one centimetre. While the researchers concede that some of the other forms may be not be biological, they argue the “tree-like” branched fossil is most likely biological, as there are no known purely chemical reactions that could have created it.

The authors also explain how the microorganisms might have obtained their energy. Chemical by-products imply the ancient microbes lived off iron, sulphur and possibly also carbon dioxide and a form of oxygen-free photosynthesis.

Lead author Dr Dominic Papineau of University College London said, “Using many different lines of evidence, our study strongly suggests a number of different types of bacteria existed on Earth between 3.75 and 4.28 billion years ago.”  

“This means life could have begun as little as 300 million years after Earth formed. In geological terms, this is quick – about one spin of the Sun around the galaxy,” he added.

Another tantalising aspect of the research is what it might mean about the possibility of life in other parts of the universe.

“These findings have implications for the possibility of extra-terrestrial life. If life is relatively quick to emerge, given the right conditions, this increases the chance that life exists on other planets,” Papineau said.

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