Cells found inside ancient rocks, their DNA stained with a green fluorescent dye
Y. Suzuki, SJ Webb, M. Kouduka et al. 2024/ Microbial Ecology
Microorganisms have been found living in tiny cracks inside a 2-billion-year-old rock in South Africa, making it the oldest rock known to harbor life. The discovery could provide new insights into the origins of life on Earth and guide the search for life beyond our planet.
We already knew that deep within the Earth’s crust, away from sunlight, oxygen and food sources, billions of hardy microorganisms survive. Living in extreme isolation, these thriving microbes divide at a glacial pace, sometimes taking thousands or even millions of years to complete cell division.
“So far, the oldest rocks in which microbes have been found are 100-million-year-old seafloor sediments,” he says. Yohey Suzuki at the University of Tokyo. “We know it’s possible to grow microbes using something in those ancient rocks.”
Now, Suzuki and his colleagues have pushed back that record by nearly 2 billion years. They obtained a 30-centimeter-long cylindrical rock core 15 meters below the surface of the Bushveld Igneous Complex in northeastern South Africa, a vast volcanic rock formation that formed more than 2 billion years ago. When they split the core, they found microbial cells living in small fractures in the stone.
The team stained the microbes’ DNA and imaged them with a scanning electron microscope and a fluorescent microscope, then compared them to potential contaminants to confirm they were native to the rock sample. They also noted that the microbial cell walls were intact, a sign that the cells were alive and active.
“Have you seen the rocks of a volcano? Do you think anything can live in those rocks?’ says Suzuki. “I certainly didn’t, so I was very excited when we found the microbes.”
The team believes that the microorganisms were carried to the rocks by water shortly after their formation. Over time, the rock became clogged with clay, which provided the nutrients necessary for microorganisms to live.
“The microbes in these deep rock formations are evolutionarily very primitive,” says Suzuki, who now hopes to extract and analyze their DNA to learn more about them. Understanding these ancient organisms can provide clues about what Earth’s first life forms might have looked like and how life evolved over time.
This discovery could have important implications for the search for life on other planets. “Rocks from the Bushveld Igneous Complex are very similar to rocks on Mars, especially in terms of age,” says Suzuki, so it’s possible that microorganisms persisted on the Martian surface. He believes that applying the same technique to separate contaminating and native microbes in Martian rock samples could help detect life on the Red Planet.
“This research suggests that the deep underground is an important environment for microbial life,” he says. Manuel Reinhardt at the University of Göttingen, Germany. “But the microorganisms themselves are not 2 billion years old. After the cracks were created they colonized the rocks; the period still needs to be investigated.”
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