The Earth is about 4.54 billion years old, and the oldest undisputed life on our planet appears as bacterial “microfossils” 3.5 billion years ago. But because bacteria are already quite complicated organisms, it’s a good bet that life (however you define it), began well before that. But how long? The seas weren’t around much before about 4 billion years (the Earth was too hot), and there was no oxygen. Life, if it existed about then, was probably adapted to extreme temperatures and was anaerobic (not requiring oxygen).
A new paper in Nature by Matthew Dodd et al. (free access, reference below) has reported what may be traces of life (iron-containing filaments and tiny tubes) that resemble the kind of life found in modern hydrothermal vents, as well as in undisputed microfossils. The age of the sediments, which are from Hudson Bay in Quebec, Canada, spans a range between 3.77 and 4.28 billion years. They can’t narrow it down much more than this large range, and of course the press is concentrating on the 4.28-billion-year date, because that’s about the earliest life could have formed given the state of the Earth then.
I won’t go into detail about the paper: it’s a hard slog even for an evolutionary biologist, for it’s largely geology and paleobiology. But one expert I asked said that the results are very interesting but not conclusive, and that the age range of course is quite large. Here are a few photographs of what may be the remnants of ancient bacteria. First are the filaments (click to enlarge pictures):
And the tubes:
These of course are not microfossils themselves, which are the fossilized remains of ancient bacteria, but simply traces of what may be ancient bacteria.
Carl Zimmer’s article about the find in Tuesday’s New York Times also shows that some experts are dubious. Several seem to think the find represents real organisms, while others think they’re artifacts. Here’s a bit of Zimmer’s piece:
But many experts in the field were skeptical of the new study — or downright unconvinced.
Martin J. Van Kranendonk, a geologist at the University of New South Wales, called the patterns in the rocks “dubiofossils” — fossil-like structures, perhaps, but without clear proof that they started out as something alive.
. . . And if these are fossils 4.2 billion years old, then scientists will have evidence that life began quickly on Earth, not long after the oceans formed.
Yet Frances Westall, the director of research at the CNRS-Centre de Biophysique Moléculaire in Orléans, France, isn’t convinced these are fossils at all. “I am frankly dubious,” she said.
For one thing, she has argued, the filaments in the Nuvvuagittuq rocks are too big. She and her colleagues have found filaments formed by bacteria in rock dating back 3.3 billion years, and these are far smaller.
On the early Earth, bacteria were forced to stay small, Dr. Westall said, because the atmosphere did not yet have enough oxygen to fuel their growth.
From someone more enthusiastic:
“I think the authors have done a good job,” said David Wacey, who researches the origins and evolution of life at the University of Western Australia. With the new evidence, he said, “One comes up with a pretty convincing biological scenario” for the origins of the mysterious rock features.
Dr. Wacey was not surprised that the new work had drawn criticism. “It may be many years before a consensus is reached,” he said. “But this is how science progresses.”
I think the last sentence is the operative one. This is by no means evidence for early life, or even for its age, but it was certainly worth publishing and will doubtlessly lead to more work. If life really did exist 4.3 billion years ago, then it means that it didn’t take long after Earth’s conditions were “right” for carbon-based and water-requiring life to begin proliferating.
Dodd, M. S., D. Papineau, T. Grenne, J. F. Slack, M. Rittner, F. Pirajno, J. O’Neil, and C. T. S. Little. 2017. Evidence for early life in Earth’s oldest hydrothermal vent precipitates. Nature 543:60-64.