BBC Space Documentary We are the Aliens
Clouds of alien life forms are sweeping through outer space and infecting planets with life. The idea that life on Earth came from another planet has been around as a modern scientific theory since the 1960s when it was proposed by Fred Hoyle and Chandra Wickramasinghe. 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.