Researchers have identified a series of fossils which they believe are the oldest living organisms ever discovered on our planet, pre-dating their closest competitor for the title by approximately 1 billion years.
Using recently-developed and extremely rare technology, known as a Secondary Ion Mass Spectrometer (SIMS), the researchers spent over a decade painstakingly examining the microfossils to determine whether they were indeed organic matter and, if so, exactly how old they were. The specimens were taken from a piece of rock found in Western Australia that was radiometrically dated as being roughly 3.5 billion years old.
“Life had to have begun substantially earlier — nobody knows how much earlier — and [this] confirms it’s not difficult for primitive life to form and to evolve into more advanced microorganisms,” says Schopf.
The findings were published December 18, 2017 in the Proceedings of the National Academy of Sciences, and the research was led by J. William Schopf, professor of paleobiology at UCLA, and John W. Valley, professor of geoscience at the University of Wisconsin–Madison.
The research centered around 11 microbial specimens from five species, or 'taxa' as they are referred to in the research paper. Some have chemical signatures similar to now-extinct bacteria and microbes from Archaea, while others are closer in appearance to microbes still found on Earth today. They also show all of the characteristics necessary to survive on an oxygen-free planet.
The microfossils were found in 1982 but weren’t first described by Shopf and his team until 1993. Shopf then produced follow-up supporting research in 2002. The area in the Western Australian desert from which the samples were taken is one of the best-preserved regions on Earth, as it has not been subjected to the same degree of erosion and tectonic plate activity as the rest of the world. The work was partially funded by the NASA Astrobiology Institute, whose purpose is to study the origins, nature and future of life in the universe.
While there was long-standing debate as to both the authenticity of the microfossils and whether they were indeed organic at all, that argument has now been won, claims Valley.
“I think it’s settled,” he says, as cited by the University of Wisconsin-Madison News.
Using one of the few SIMS in the world, the team were able to separate out the constituent isotopes in the carbon from which the fossils are composed and then measure their ratios to allow for further, and more accurate, dating.
“The differences in carbon isotope ratios correlate with their shapes,” Valley says. “If they’re not biological there is no reason for such a correlation. Their C-13-to-C-12 ratios are characteristic of biology and metabolic function.”
“These are a primitive, but diverse group of organisms,” says Schopf.
Among the organisms identified by the team are: "phototrophic bacteria that would have relied on the sun to produce energy, Archaea that produced methane, and gammaproteobacteria that consumed methane, a gas believed to be an important constituent of Earth’s early atmosphere before oxygen was present."
The process to even begin examining the fossils themselves, encapsulated in a hard layer of quartz, involved painstaking grinding and polishing the specimens one micrometer at a time. For perspective, each microfossil is approximately 10 micrometers wide, and a human hair is roughly 80 micrometers in width. The SIMS can study sample sizes ranging from 1 to 10 micrometers.
“We have no direct evidence that life existed 4.3 billion years ago but there is no reason why it couldn’t have,” says Valley. “This is something we all would like to find out.”
“People are really interested in when life on Earth first emerged,” Valley says. “This study was 10 times more time-consuming and more difficult than I first imagined, but it came to fruition because of many dedicated people who have been excited about this since day one … I think a lot more microfossil analyses will be made on samples of Earth and possibly from other planetary bodies.”
However, the title of ‘world’s oldest living organism’ is widely coveted within the scientific community and researchers frequently claim to have made the definitive discovery.
In addition, David Wacey, a scientist at the University of Western Australia’s Centre for Microscopy, Characterisation and Analysis, disputes the findings of the research, questioning the methodology and accuses the researchers of ‘deliberate ignorance.’
“I find this manuscript to be a poor piece of science containing over-interpretations of data that are not statistically robust,” Wacey told Gizmodo. “It also shows ignorance — I assume deliberately so, rather than being unaware — of previously published work and a continued reliance on a technique (Raman spectroscopy) that has already been shown to be unfit for the purpose in which it is applied by the authors.”
Wacey said the authors have ignored previous work, including his own, which provides the most up-to-date perspective on the techniques used and directly calls into question what Valley and Schopf are claiming.
“[The] light microscope and Raman data presented here do not, in my opinion, demonstrate that these objects are microfossils, and the isotopic data are scarce and questionable. Even if the isotopic data do turn out to be technically robust, similar data could be produced by adsorption of multiple generations and/or sources of carbonaceous material onto mineral grains in a complex hydrothermal setting."
“Whether such adsorbed carbonaceous material is ultimately biogenic, non biogenic or a mixture of both is still open to debate, but these microscopic objects are not, in my opinion, microfossils.”
“It is, quite frankly, beyond belief that this paper was reviewed by Andrew Czaja, an ex-student and collaborator of lead author Schopf,” Wacey told Gizmodo. “Notably, Czaja and Schopf collaborated on several papers using the flawed Raman technique on exactly this Apex material [here, here, and here]. This raises serious questions about the editorial processes within PNAS.”