Scientists have uncovered what could be the oldest directly dated evidence of life on Earth in a 3.4-billion-year-old rock from eastern India, revealing chemical traces that point to ancient microbial activity.
The discovery was made in the Singhbhum geological block, where researchers found carbon-rich material preserved between thin layers of silica. The rock, known as Bhitardari chert, contains dark bands of carbon alternating with pale quartz, preserving a remarkably old record of the environment in which it formed.
An international team of scientists analysed the samples using Raman spectroscopy and carbon-isotope analysis. Their findings suggest that the carbon-rich material has characteristics consistent with a biological origin and may have been produced by primitive microorganisms living in an ancient marine environment.
The research dates the material to approximately 3.497 billion years ago, placing it in the Palaeoarchaean Eon, a period spanning roughly 3.6 billion to 3.2 billion years ago. If confirmed, the finding would represent the oldest directly dated rock containing a convincing biosignature.
The Bhitardari chert formed in an ancient sea associated with volcanic and hydrothermal activity. Hot, silica- and iron-rich fluids circulating beneath the seafloor would have supplied chemicals and nutrients that could support early microbial communities.
Researchers were able to establish the age of the rock using eight zircon crystals embedded in the sample. Because chert itself often lacks minerals suitable for direct dating, the zircon grains provided an important geological clock. Their characteristics indicate that they were deposited as volcanic ash settled over the sediments as the rock formed.
The researchers believe that microbial mats may have occupied these ancient marine environments and that traces of their activity survived the immense geological changes that transformed the planet over billions of years.
Chemical fingerprints of ancient life
To determine whether the carbon-rich material was biological, the scientists examined its chemical composition using Raman spectroscopy and carbon-isotope analysis.
Carbon occurs naturally in different forms, or isotopes. Living organisms generally favour the lighter carbon-12 isotope over carbon-13 during biological processes, leaving behind a distinctive chemical signature. The isotope pattern found in the Bhitardari chert is consistent with carbon fixation, a process through which organisms convert carbon dioxide into organic material needed for growth.
The findings also point towards metabolic processes that may have existed in some form as early as 3.5 billion years ago. Researchers identified signatures potentially associated with pathways such as the Calvin cycle, used in photosynthesis, and the acetyl-CoA pathway, which plays a central role in the metabolism of proteins, carbohydrates and fats.
The authors, affiliated with research institutions in India, France, the Netherlands, the United States and Oman, said ancient marine systems associated with volcanic and hydrothermal activity could have provided the nutrients and chemical ingredients necessary for the development of some of Earth’s earliest microbial ecosystems.
The study, published in the Proceedings of the National Academy of Sciences of the United States of America, adds the Singhbhum Craton to the growing body of evidence about the planet’s earliest life.
Earlier candidates for ancient organic matter and possible microbial life have been identified in rocks from Australia, Greenland and South Africa. However, the researchers say the combination of the biological chemical signature and the precisely dated zircon crystals in the Indian sample provides unusually strong evidence for its great antiquity.
If the interpretation is upheld, the Singhbhum discovery could offer one of the clearest glimpses yet into life during Earth’s earliest chapters — when microscopic organisms were already thriving in oceans more than three billion years before humans appeared.
