Ancient Indian rock may hold earth’s oldest life signs
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Researchers in India examined a 3.5 billion-year-old rock formation and found a chemical signature suggesting the presence of ancient life.
The team, led by Trisrota Chaudhuri of the Geological Survey of India, studied rock samples from the Singhbhum craton, one of Earth’s oldest crustal regions. They dated the rock to 3.497 billion years ago, with a margin of error of about 5 million years, making it potentially the oldest rock containing a biosignature, a chemical trace linked to life.
To determine the rock’s age, scientists analyzed tiny zircon crystals within the chert, a silica-rich rock formed on the seabed. These crystals retained information from volcanic ash deposited during the rock’s formation. The team then investigated the carbon found within the rock, noting that living organisms tend to utilize lighter carbon isotopes. The carbon in the Indian sample displayed a ratio consistent with biological carbon fixation, specifically a value of −30.9 per mille.
This suggests the material may have passed through the metabolism of ancient organisms. The rock’s structure, with alternating layers of silica and carbon-rich material, further supports the possibility of ancient microbial mats, communities of microorganisms forming layered structures. While no fossilized cells were found, the combined evidence indicates biological processes may have been active nearly 3.5 billion years ago.
Researchers now plan to search for similar rocks in the Singhbhum craton to better understand how common life may have been in ancient seas.
