The oldest traces of life on Earth have been found

Scientists have for the first time directly determined the age of some of the oldest traces of life on Earth: the remains of microbial communities discovered in India turned out to be approximately 3.5 billion years old. Until now, such findings had been dated only indirectly — by the age of the surrounding rocks. The results of the study have 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 most ancient blocks of Earth's crust. Preserved in the carbonaceous rock were the remains of microbial mats — fossilized "carpets" of single-celled organisms that lived side by side and formed distinctive ancient biofilms.

The main breakthrough was that the age was determined directly within the rock itself. To achieve this, the researchers measured the ratio of uranium and lead isotopes in zircon crystals and obtained a value of 3.497 billion years with a margin of error of approximately 5 million years. The zircon crystals turned out to be fresh volcanic ones rather than transported from elsewhere, meaning their age directly reflects the time of existence of the microbes themselves.

The biological origin of the carbon is also indicated by its isotopic composition: it has a reduced content of the heavy carbon-13 isotope, which living organisms "under-incorporate" during metabolism. Additional arguments include the fine layering of the rock, characteristic of microbial mats, as well as evidence that the rock was not subjected to heating above temperatures at which such biological "signatures" are destroyed.

The work was led by Trisrota Chaudhuri of the Geological Survey of India. According to the authors, direct dating makes conclusions about the antiquity of life significantly more reliable and opens the way to more precise study of its earliest traces on the planet. This is also relevant for the search for life beyond Earth: understanding the most ancient biosignatures will help recognize similar signs on other planets.