Gilbert Levin, a NASA engineer who worked on the Viking missions, says he’s “convinced we found evidence of life of Mars in the 1970s.”

In a Scientific American article published today, Levin explains how two separate craft landed on the surface of the red planet and conducted a series of tests to determine if there were was life.

One particular test, based on the same experiment Louis Pasteur conducted to prove the existence of microbes, came back positive.

The results were confirmed in a replica test by another craft 4,000 miles away.

Levin’s spent the 43 years since studying the results.

As the experiment progressed, a total of four positive results, supported by five varied controls, streamed down from the twin Viking spacecraft landed some 4,000 miles apart.

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