Scientists for the first time have confidently identified on Mars a collection of carbon molecules used and produced by living organisms.
That does not prove that life has ever existed on Mars. The same carbon molecules, broadly classified as organic matter, also exist within meteorites that fall from space. They can also be produced in chemical reactions that do not involve biology.
But the discovery, published on Thursday by the journal Science, is a piece of the Mars puzzle that scientists have long been seeking. In 1976, NASA's two Viking landers conducted the first experiments searching for organic matter on Mars and appeared to come up empty.
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