Scientists have discovered the oldest traces of life on Earth

Scientists have for the first time directly dated some of the oldest traces of life on Earth: the remains of microbial communities from India turned out to be approximately 3.5 billion years old. Previously, such finds were dated only indirectly — by the age of the surrounding rocks. The work has been published in the journal Proceedings of the National Academy of Sciences (PNAS).

The discovery was made at the Bhitardari site in the Singhbhum Craton — one of the oldest blocks of Earth's crust. The carbonaceous rock preserved the remains of microbial mats — fossilized "carpets" of single-celled organisms that lived together, a kind of ancient biofilm.

The key breakthrough was that the age was determined directly within the rock itself. To do this, the scientists measured the ratio of uranium and lead isotopes in zircon crystals and obtained a value of 3.497 billion years with an uncertainty of about 5 million years. Since the zircon crystals turned out to be fresh volcanic ones rather than transported from elsewhere, their age reflects the time when the microbes themselves were alive.

The biological origin of the carbon is also indicated by its isotopic composition: it contains less of the heavy carbon-13 isotope, which living organisms "underincorporate" during metabolism. Additional evidence includes the fine layering of the rock, characteristic of microbial mats, and data showing that the rock was never heated above temperatures at which such biological "signatures" are destroyed.

The work was led by Trisrota Chaudhuri from the Geological Survey of India. According to the authors, direct dating makes the conclusion about the antiquity of life far more robust and opens the way to more precise study of its earliest traces on the planet. This is also important for the search for life beyond Earth: understanding the oldest biosignatures helps recognize similar signs on other planets.