Researchers found traces of possible life in 3.95-billion-year-old rocks from the Torngat Mountains of northern Labrador, Canada. If confirmed, this would be the oldest signs of life yet discovered, reports Emily Chung for CBC News.
In recent years, geologists have seemingly been locked in a race to find Earth's oldest life. In 2016 alone multiple research teams have pushed back the date that life may have started taking shape. In August, researchers published a study documenting 3.7 billion year old bacteria fossils found in Greenland. In March, another team announced the discovery of possible traces of bacterial life at least 3.77 billion years old. The latest find, detailed in the journal Nature, is even older, beating that last discovery by 150 million years.
As Ed Yong reports for The Atlantic, the latest fossil is actually tiny crystals of the carbon mineral graphite that has a specific isotopic signature, which suggests that it was left by the bustling activity of microbial life.
In nature, carbon atoms come in two stable isotopes: carbon-12 and the heavier carbon-13. Living organisms, however, tend to favor carbon-12 because it is easier to transform into living tissue, Yong explains. When the critters die and decompose, they leave behind a carbon residue that contains much more of this particular isotope.
But it's not just the isotopic composition that had the researchers excited. The orderly structure of the graphite grains also suggest that the carbon went through the same heating that created the rocks around them, Yong writes. This means that it's unlikely that younger carbon somehow infiltrated the formation.
Such discoveries are changing how scientists think about early life. “The emerging picture from the ancient-rock record is that life was everywhere,” Vickie Bennett from Australian National University, not involved in the study tells Yong. “As far back as the rock record extends—that is, as far back as we can look for direct evidence of early life, we are finding it. Earth has been a biotic, life-sustaining planet since close to its beginning.”
Even so, similar to prior claims of oldest life, the newest discovery has stirred up controversy. It's possible that inorganic processes could create the carbon-12-rich graphite, and more evidence is needed to support the claims that the material is from organisms.
Martin Whitehouse, researcher at the Swedish Museum of Natural History tells Ian Sample at The Guardian, he has major doubts. Whitehouse, who wasn't involved with the research, says he doesn't trust the study's method of dating the carbon. “Regardless of the veracity of the biogenic evidence from the graphite, the claim that it is the oldest requires that the geochronology is watertight,” he says. “If it’s younger than about 3.8 billion years, it isn’t very exciting anymore.”
Others remain impressed with the find. “This is an excellent paper with lots of information and another definite proof that life existed back in the Eoarchean,” Dominic Papineau who studies Earth’s earliest life at the University College London tells George Dvorsky at Gizmodo. “I think the authors make a solid case, although it could have been further compelling by looking at the elemental and molecular compositions of the graphite and the mineral associations with the graphite.”
These elemental compositions are part of what the researchers hope to do next. As lead author Tsuyoshi Komiya of The University of Tokyo tells Agence France-Presse, “we will analyze other isotopes such as nitrogen, sulphur and iron of the organic matter and accompanied minerals.” They hope that these additional analyses could help them further tease apart the mystery behind the critter that left the carbon traces.