Chemical evidence of life uncovered in SA rocks 3.3bn years old

Chemical evidence of life has been uncovered in South African rocks 3.3 billion years old, doubling the timelines for this window into our deep past and charting a new scientific trail that could help detect the spoor of life on other planets. 

The findings, presented by scientists on Monday, 17 November in the Proceedings of the National Academy of Sciences, push back the dating on this front by an astonishing 1.6 billion years. The earliest such traces had previously been detected in rocks 1.7 billion years old. 

Spearheaded by scientists from the Carnegie Institution for Science in collaboration with several other institutions, the study, which combined state-of-the-art chemistry with artificial intelligence (AI), also found evidence of oxygen-producing photosynthesis 2.5 billion years ago, extending this timeline back by 800 million years.

This finding was also yielded from South African geology – the 3.3-billion-year-old evidence of life from the Josefsdal Chert near Barberton in Mpumalanga, while the earliest known evidence of photosynthesis was found in the Gamohaan Formation near Kuruman in the Northern Cape. 

“Besides helping find evidence of Earth’s earliest life, this work advances a potential way to identify traces of life beyond our planet,” Carnegie Science said in a statement announcing the findings.

“The new work is based on the hypothesis that life’s molecules are rigorously selected for their biological functions – in keeping with a new law of nature proposed in 2023 ... (It) suggests that the distribution of bio-molecular fragments found in old rocks still preserves diagnostic information about the biosphere, even if no original biomolecules remain.”

The team studied 406 samples taken from an assortment of examples, including modern plants and animals, fossils and ancient sediments from five continents, to see if there were traces of life after the original biomolecules had vanished. 

The team used pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) to release trapped chemical fragments from each sample and then used pioneering machine learning to unlock the secrets within.

The sample near Barberton showed that it was a living organism 3.3 billion years ago. 

“From it we were able to show, with quite some confidence, even though there is not a single trace of what would look like a bio-molecule, that their distribution through the rock shows us, through machine learning or AI, that the rock was once a living system,” Dr Bob Hazen, a senior staff scientist at the Carnegie Institution’s Geophysical Laboratory and one of the study’s co-authors, told Daily Maverick in a telephone interview. 

“We have taught AI how to read the chemical fingerprints of life. It’s like reading these fossilised whispers of ancient life.”

The scientists involved are also careful not to overstate their conclusions, and acknowledge the need for wider and more balanced data sets while noting that this method is complementary to and not a replacement for more traditional approaches.

That’s how science works – evidence is gathered over time, which can support or call into question initial conclusions that are reached. It is an unfolding saga. 

Holy Grail

While there is fossil evidence of life older than 3.3 billion years, this is the first time that its molecular chemical fingerprints have been detected through high-tech sleuthing.

“The notion that evidence of life has been found from four billion years ago is still quite controversial. There are some larger fossils known as stromatolites, and these are layered rocks that have a mound-like structure, and they are taken as signs of fossil life. But they don’t contain any molecules or bio-material,” said Hazen. 

“So one of the Holy Grails of palaeontology has been to be able to take a rock that has no fossils at all – an old, black rock that has carbon – and see if that carbon comes from meteorites, a non-biological process, or was in fact once alive.”

These signals can now be detected even after billions of years by unpacking the distribution of ancient molecules. 

“What we found was the molecules themselves, any individual molecule, doesn’t really tell you very much. But when we take all the different little molecules and look at them together, their distribution from a living rock is very different from the distribution of a rock that was never alive,” Hazen said. 

Pushing back the timeline on photosynthesis – the process through which plants harness sunlight – is also a scientific game changer. 

“We are right at the beginning of an adventure here. This is the oldest by far that anyone has shown evidence of molecular photosynthesis. People assumed there had to be photosynthesis because there was a great oxidation event on Earth when life began pumping oxygen into the atmosphere, and Earth became much more oxygen-rich,” said Hazen. 

These groundbreaking methods enabled by AI have uses that go beyond life on Earth. 

“This method could also assist in the search for signs of extraterrestrial life. If AI can detect biotic ‘fingerprints’ on Earth that survived billions of years, the same technique might work on Martian rocks or even samples from Jupiter’s icy moon Europa,” Carnegie Science said in its statement. 

South Africa – geological wonderland 

The study also highlights the scientific treasure trove that is the South African landscape. From the fossil evidence of the first creatures to give rise to mammals in the Karoo to key chapters in humanity’s evolutionary journey in the Sterkfontein Caves and nearby sites, to these ancient rocks around Barberton, South Africa is a scientific gift that keeps on giving. 

“South Africa is a geological wonderland,” said Hazen.

“It holds some of the very best preserved ancient rocks anywhere on our planet. South Africa has layers of rock that were deposited 3.5 billion years ago, and you look at them and say, ‘those look just like rocks that formed in the last few million years.’ They have undergone very little alteration.” 

Indeed, he said work that had not yet been published drew on samples from the Barberton site that dated back 3.5 billion years. 

“Now that we have this new method, we should be able to take those specimens from South Africa and push that record of life back even farther,” Hazen said.

Stay tuned: these findings will be uncovered at a faster pace than geological time. DM