the fundamental life form

Several years ago, when I was a graduate student at Macquarie University, Daniel Dennett came and spoke. For months I had heard philosophers talk at length about the flaws in Dennett's reasoning and the problems with his epistemolgical stance. "Rampant externalist" was a phrase I heard applied to him, with a tone that suggested it was intended as an insult. But when they had the chance to actually raise their concerns, they sat up the back and said nothing. The questions to Dennett at the end of his talk were either from curious students or Dennett fans.
Much of what Dennett said was stuff covered in his books. He also talked about change-blindness and gave a demo. Change-blindness is always a sure-hit crowd pleaser if you are talking about consciousness or the mind, although for someone who has done the circuit of consciousness seminars, it was less than enthralling.
For me, the most interesting point he made was a comment in response to a question, and it has stayed with me to this day. I forget the question, which at any rate was only marginally connected to Dennett's answer.
He suggested that the fundamental, unchanging form of life throughout the universe is bacteria. Bacteria, he pointed out, was here at the beginning. Bacteria will be here when we are long gone. Bacteria live deep in the ocean and in the highest reaches of the atmosphere. Furthermore, bacteria are known to be able to survive in space, and have probably travelled between the planets of the solar system. In fact, it is not implausible to think that bacteria are spread throughout the universe.
Dennett believes that multi-cellular life forms, like trees, fish, and humans, arise from single-cell bacteria. This evolutionary step could occur anywhere. However, at some level of complexity, the edifice falls apart. For example, humans may develop the ability to destroy life on earth. So, Dennett suggested, perhaps complex life is a chance event, that pops up around the universe like sparks in a fire, surviving briefly - in universal terms - before dying down again into the eternally smouldering embers of bacteria.
I have since learned that this idea did not originate with Dennett, but is a theory dating back centuries. The theory is referred to as panspermia.
As Greg Clark of space.com says, they thrive in the arctic, so why not on Mars? There could be life there despite the findings of the Viking space expedition.