By Will Dunham

WASHINGTON (Reuters) -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,

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