An international group of researchers, led by Brazilians, has just developed a method to investigate microfossils inside rocks without destroying them, creating a 3D nanotomography of their structure. Scientists hope to use the technique in the future to search for signs of life in samples coming from Mars.
The work has as its first author Lara Maldanis, a researcher at the National Synchrotron Light Laboratory (LNLS), in Campinas (SP), currently in post-doctorate at the University of Grenoble, France. The article describing the results was published in this week's issue of Scientific Reports.
The researchers worked with a sample of the Gunflint Formation in Canada. “It is a true icon in the study of ancient life on Earth,” says Maldanis. It is one of the best documented regions of ancient fossils, going back to a time when the Earth was inhabited only by simple microorganisms, such as bacteria and archaea.
The technique involves cutting out a small piece of the rock, containing the structures of interest, in the form of a tube of just 25 micrometers (thousandths of a millimeter), and then subjecting it to an X-ray scan generated by a synchrotron light source ( the researchers used the one from SLS, Fonte de Luz Switzerland, at the Paul Scherrer Institute, in Viligen).
The result is an X-ray computed nanotomography that produces a 3D image of what remains of bacterial cells that lived billions of years ago. In this case, 1.88 billion years. "The technique allows us to see the cell from all angles, and this is very important when trying to differentiate a fossil bacterium, which is sometimes just a tiny sphere or filament without any ornamentation, crystals or simple clumps of organic matter" says Maldanis.
Photograph of the sample (a) and 3D nanotomography result, in the same orientation as seen in the photo (b) and at other angles (c and d). The scale bar has 5 micrometers. (Credit: Maldanis et al.)
Until then, the only technique capable of producing something like this involved scanning electron microscopy, with an aggravating factor: “To be able to see the fossil in 3D, it was necessary to remove layer by layer, destroying it completely”, highlights the researcher. “Our technique, in addition to not being destructive, has the added advantage of having a great contrast to the organic matter of the cells.”
On the Brazilian side, the work is financed by Fapesp (São Paulo State Research Support Foundation) and Instituto Serrapilheira, within the scope of the astrobiology project led by Douglas Galante, a researcher at LNLS. And the expectation, of course, is that this is just the beginning. With the technique properly demonstrated, the researchers hope to explore other samples and explore some of the questions that disturb scholars in the first steps of life on Earth.
"Now we are convinced that this technique can contribute a lot to some very interesting discussions", says Maldanis. “We would love to test, for example, the Apex Chert microfossils in Australia, described as the oldest fossils on Earth, but which have been the subject of discussion and controversy for more than 20 years!”
And why stop on land samples? The group hopes to apply the method, for example, to some sample of the famous meteorite ALH84001, coming from Mars. Researchers at NASA in 1996 said they had identified nanofossils of possible Martian microbes in it. Today the scientific consensus is that these are non-biological structures, but the authors of the research to date are betting on its original conclusion and perhaps a more sophisticated imaging technique can put an end to the question, to one side or the other. It is not easy for NASA to borrow a meal from the ALH84001, but Brazilian researchers have not yet given up.
And the prospect of studying Martian rocks takes on even more interesting features as space agencies begin to set up a plan to bring in new samples from Mars. One of the goals of the Perseverance jeep, which departs in July, is to collect samples of interest, for future sending back to Earth. “We want to show with this work, and those that are yet to come, that a synchrotron can be the best place to study them”, says Maldanis. "And who knows, even if you are not going to dream a lot, some of these analyzes may not be done on our Sirius (new synchrotron light accelerator under construction at LNLS)?"