At the time they were ridiculed for their idea – known as panspermia. But now, with growing evidence, it's back in vogue and even being studied by NASA.

We meet the scientists on a mission to get to the bottom of the beginnings of life on Earth - from the team in Texas who are lovingly building a robotic submarine called DEPTHX to explore a moon of Jupiter, to Southern India where they are investigating a mysterious red rain which fell for two months in 2001.

According to local scientist Godfrey Louis, the rain contains biological cells unlike any he had seen before – with no DNA and the ability to replicate at 300°C. Louis has come to the conclusion that the cells are extra-terrestrial in origin.

The Real Reason NASA Never Returned To The Moon