Washington - Danish researchers said yesterday they had found what they think may be evidence of the oldest life on Earth - a signature left by plankton 3.7 billion years ago.
There is no standard fossil evidence of the plankton, but Mr Minik Rosing and colleagues at the Geologisk Museum in Copenhagen looked for a chemical signature in ancient rocks in west Greenland.
"The oldest known fossils have an age of 3,500 million years ago and may represent photosynthetic cyanobacteria," they wrote in a report in the journal, Science. These are bacteria that, like plants, use the sun's energy to feed themselves.