in 3.7 billion year old rocks:
Scientists claim to have found the oldest evidence of photosynthesis - the most important chemical reaction on Earth - in 3.7-billion-year-old rocks.
Photosynthesis is the process by which plants, algae and certain bacteria convert sunlight to chemical energy.
Danish researchers say rocks from Greenland show life-forms were using the process about one billion years earlier than has previously been shown.
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http://news.bbc.co.uk/2/hi/science/nature/3321819.stm