New method spots signs of primordial life in ancient rocks

Scientists have detected some of the oldest signs of life on Earth using a new method that recognizes chemical fingerprints of living organisms in ancient rocks, an approach that also holds promise in the search for life beyond our planet.
The researchers found evidence of microbial life in rocks about 3.3 billion years old from South Africa, when Earth was roughly a quarter its current age. They also found molecular traces left by microbes that engaged in oxygen-producing photosynthesis – conversion of sunlight into energy – in rocks about 2.5 billion years old from South Africa.
The scientists developed an approach, harnessing machine learning, to distinguish in ancient rocks between organic molecules with a biological origin – like from microbes, plants and animals – and organic molecules with a nonliving origin at greater than 90% accuracy. The method was designed to discern chemical patterns unique to biology.
“The remarkable finding is that we can tease out whispers of ancient life from highly degraded molecules,” said Robert Hazen, a mineralogist and astrobiologist at the Carnegie Institution for Science and co-lead author of the study.
Scientists hunting for evidence of Earth’s earliest life have relied primarily on finding fossil organisms. Earth formed approximately 4.5 billion years ago. Its first living organisms may have been microbes that arose perhaps hundreds of millions of years later at marine hydrothermal vents or terrestrial hot springs.