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Most animals (excluding the seemingly immortal among us) are defined by relatively short lifespans. While we might live "long and full lives," as the saying goes, our time in the universe is merely an attosecond in the grand timeline of all things. But the world of microbes plays by different rules.
In 2020, for example, scientists successfully revived 100-million-year-old microbes, making them the longest-lived microbes known to science. Now, researchers from the University of Tokyo report that they cracked open rich ore deposits gathered from the Bushveld Igneous Complex in northeastern South Africa and, surprisingly, found two-billion-year-old microbes living within the sample. While this certainly smashes the microbial lifespan world record, the microbes also showed little evolutionary changes due to their extreme isolation, allowing them to serve as a remarkable glimpse into Earth's distant past. The results of the study were published in the journal Microbial Biology.
"We didn't know if 2-billion-year-old rocks were habitable," University of Tokyo's Yohey Suzuki, lead author of the study, said in a press statement. "Until now, the oldest geological layer in which living microorganisms had been found was a 100-million-year-old deposit beneath the ocean floor, so this is a very exciting discovery. By studying the DNA and genomes of microbes like these, we may be able to understand the evolution of very early life on Earth."
Bushveld Igneous Complex is well-known for its ore samples, as this rocky intrusion formed as magma cooled below the Earth's surface. Remaining remarkably stable since its formation, this has allowed pockets of ancient microbial life to flourish. Upon obtaining a 30-centimeter-long rock core sample located 15 meters below ground, scientists cut the core into slices to reveal a sample so densely packed with clay that microbes couldn't leave and nothing else could enter, effectively preserving the microbes for a couple billion years.
To make sure the sample wasn't contaminated upon extraction, the team first detected the microbes using optical photothermal infrared (O-PTIR) spectroscopy, then stained them with a green solution. The samples were then examined with a scanning electron microscope and a technique called fluorescent microscopy. This three-pronged approach successfully determined that the microbes had indeed been trapped within the rock for two billion years.
Such a discovery is a huge glimpse into the formation of life on Earth, as well as a unique look into the history of evolution on this planet. However, the researchers are also interested in what this discovery means for life beyond this planet -- particularly, Mars. Recent data gathered by NASA's Mars Reconnaissance Rover suggests that water possibly flowed on the Red Planet as late as 2.5 to 2 billion years ago. If two billion-year-old microbes could be found on Earth, it's possible that similar microbes are locked away in Martian soil as well.
"NASA's Mars rover Perseverance is currently due to bring back rocks that are a similar age to those we used in this study," Suzuki said in a press statement. "Finding microbial life in samples from Earth from 2 billion years ago and being able to accurately confirm their authenticity makes me excited for what we might be able to now find in samples from Mars."