Scientists have uncovered chemical evidence of life in 3.3-billion-year-old rocks from South Africa, offering some of the earliest signs of living organisms ever found on Earth. The discovery pushes back the molecular record of life and supports long-standing theories about early microbial activity on a planet that was then just a quarter of its current age.
The research team used a machine learning technique to analyze organic molecules preserved in ancient rock. The method identifies patterns specific to molecules formed by living organisms, such as microbes, plants, or animals.
By applying this tool, scientists were able to distinguish biological signatures from nonliving chemical processes with more than 90 percent accuracy.
Machine learning reveals hidden traces of ancient life
The study also uncovered molecular traces of microbes capable of oxygen-producing photosynthesis in rocks estimated to be 2.5 billion years old, also from South Africa.
This suggests that such photosynthetic activity began hundreds of millions of years earlier than previously recorded through molecular evidence. Over time, this process helped introduce oxygen into the atmosphere, eventually supporting the evolution of more complex life forms.
Co-lead author Robert Hazen, a mineralogist and astrobiologist at the Carnegie Institution for Science in Washington, said the technique allows researchers to detect life’s chemical remains even when the original biomolecules have broken down.
Hazen explained that what appears to the human eye as thousands of molecular peaks can be interpreted by machine learning to reveal patterns that clearly separate material that was once alive from material that was not.
Until now, scientists searching for the earliest evidence of life on Earth have relied mainly on fossil records. However, such fossils, including stromatolites from Australia and South Africa dating back 3.5 billion years, are extremely rare. The new approach opens another path by detecting fragmented organic compounds that still retain the chemical fingerprint of life.
Scientists use new tools to trace evidence of life on early Earth
Anirudh Prabhu, the study’s co-lead author and a data scientist at Carnegie, said the findings significantly expand the timeline for detecting life, doubling it from 1.6 billion to 3.3 billion years. He noted that the method also distinguishes between types of organisms, such as those capable of photosynthesis, even in degraded samples.
The technology could prove useful in astrobiology, with NASA already collecting rock samples on Mars and identifying other promising sites like the moons of Jupiter and Saturn.
The research team has received NASA funding to refine the method for use in space missions. Hazen emphasized that applying this technique to Martian samples or the organic plumes of moons such as Enceladus and Europa could help determine whether life ever existed beyond Earth.
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