Cells found inside ancient rocks, whose DNA is stained with a green fluorescent dye
Y. Suzuki, SJ Webb, M. Kouduka et al. 2024/ Microbial ecology
Microbes have been discovered living in tiny cracks in a 2 billion-year-old rock in South Africa, making it the oldest rock known to have harbored life. The discovery could provide new insights into the origins of life on Earth, and could even lead to the search for life beyond Earth.
We already knew that billions of resilient microorganisms survive deep in the Earth’s crust, far from sunlight, oxygen, and food sources. Living in extreme isolation, these slow-growing microorganisms divide at a glacial pace, sometimes taking thousands or even millions of years to complete cell division.
“So far, the oldest rocks in which microorganisms have been found are marine sediments from 100 million years ago,” says Yohei Suzuki of the University of Tokyo. “We know that something in these ancient rocks can be used by microbes to grow.”
This time, Suzuki and his colleagues have pushed back that record by nearly 2 billion years. They obtained a 30-centimeter-long cylindrical rock core from 15 meters below the surface of the Bushveld Igneous Complex in northeastern South Africa, a vast volcanic rock formation that formed more than two billion years ago. When they sliced ​​open the core, they discovered microbial cells living inside tiny cracks in the rock.
The researchers stained the microbial DNA, imaged it with scanning electron and fluorescence microscopy, and compared it to potential contaminants to confirm that they were unique to the rock samples. They also noted that the microorganism’s cell wall was still intact, indicating that the cell was alive and active.
“Have you ever seen a volcanic rock? Do you think something could live inside that rock?” Suzuki says. “I never did, so I was very excited when I found microbes.”
The researchers believe that the microbes were brought into the rocks through water shortly after they formed. Over time, the rocks may have become clogged with clay, providing the microorganisms with the nutrients they needed to survive.
“The microorganisms that exist in these deep rock layers are very primitive from an evolutionary perspective,” Suzuki says. He now wants to extract and analyze the microorganism’s DNA to learn more about it. Understanding these ancient organisms may provide clues about what the earliest life forms on Earth were like and how life evolved over time .
This discovery could also have important implications for the search for life on other planets. “The rocks of the Bushveld Igneous Complex are very similar to the rocks of Mars, especially in terms of age,” Suzuki says, so it’s possible that microbes persist beneath the surface of Mars. He believes that applying the same technique to distinguish between contaminant and indigenous microorganisms in Martian rock samples could help detect life on Mars.
“This study further strengthens the view that the deep underground is an important environment for microbial life,” says Manuel Reinhardt of the University of Göttingen in Germany. “But the microorganisms themselves have not lived for two billion years. They colonized the rock after the formation of cracks. The timing still needs to be investigated.”
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