A former NASA scientist says we have already discovered alien life

In an op-ed , Gilbert Levin says Viking missions to Mars uncovered signs in 1976

Four Mars soil samples turned up positive in initial tests for microorganisms 

NASA says it was never able to actually definitively prove their existence  

The hunt for alien life may have ended in the 1970s according to one former NASA scientists.

In an op-ed published in Scientific American titled 'I'm Convinced We Found Evidence of Life on Mars in the 1970s' former NASA scientist Gilbert Levin writes that  a mission to Mars was the first concrete example of biological life on other planets.

'What is the evidence against the possibility of life on Mars? The astonishing fact is that there is none,' writes Levin.