At least I think so. And I think it is an extremely thin limb. I just watched the latest episode. In it they state that during the first half of the Earth's life it was subject to repeated large impacts that would have wiped out all life on Earth. However, some bacteria would have lived in rocks that were ejected from the surface into space. Those life forms would have repopulated the Earth. My first objection to this is that the Late Heavy Bombardment (LHB), if it occurred happened around 4 billion years ago, long before the first half of the existence of the Earth was over around 2.5 billion years ago. The second problem I have is that I don't see why life would have survived in the rocks ejected into space, while none would have survived on the surface of the Earth. When I saw that I really started wondering what Tyson had been smoking.
Another problem I had with the show was that they brought out the theory of panspermia. That is the theory that life came to Earth from space, carried in rocks that were blasted out of some life bearing planet and drifted through space till they came to Earth, thus sowing the seeds of life on Earth. I can see that this might be possible, but I think the chances are a lot more remote than that life developed independently here on Earth. One of the problems with panspermia is that it just pushes the development of life back in time to some other planet in the remote past. It still requires that life come into being from the "primordial ooze" somewhere. Since it is obvious that life can develop then I see no reason to suppose that it would only happen once. It is much more probable that life would develop any time the conditions are right for it.
This time I think they really went over the top.
Bill Gill
