We know a lot less about early Earth life than I’d thought: Two decades ago [Schopf] … was investigating … 3.5-billion-year-old rocks that are among the oldest on Earth. In 1993, he announced that they contained 11 different types of “microfossil” that looked for all the world like modern photosynthesising cyanobacteria. … Other 3.5-billion-year-old Australian rocks contained rippling structures that looked like fossil stromatolites. … Astonishingly soon after our planet formed some 4.6 billion years ago, photosynthesising bacteria were widespread. This emerging consensus lasted only until 2002, when palaeontologist Martin Brasier of the University of Oxford unleashed a barrage of criticisms. …
I noticed the article was written by Nick Lane, who has written extensively on mitochondria and the emergence of the Eukaryote. After reading the article, I was not surprised to see that he was the author.
The implication of this is that even simple (prokaryote) life is hard to come by. This suggests that even simple life will be somewhat rare in the universe. This is testable in the near future. Kepler is supposed to find Earth-sized planets in the right orbits in the next 2 years. The successor to kepler will be able to characterize the atmospheres of some of these Earth-sized planets. If it finds that none of these exo-planets have free Oxygen atmospheres, it is reasonable to assume that even simply life is uncommon, because photosynthetic life is necessary to produce an Oxygen atmosphere. No Oxygen, no photosynthetic life. This would answer Fermi's question.
Of course, the pro-karyotes were able to create only about 10% the Oxygen that we have today. Eukaryotes were necessary to make modern Oxygen levels. If Nick Lane is correct about the likelihood of the emergence of the Eukaryote (and I think he is), the Earth is likely to be the only planet with complex life in the entire galaxy.
When we do get out into space, I think we are going to find that we live in a resource-rich, but incredibly barren universe.
I wonder why no one seems to care enough to comment on this topic. \\Maybe this is a case where you'dthink the best mindswould be on this big question but nobody's doing much work on it.
My wife is reading a book on parasites, and last night she quotes to me some passage that she thought was fascinating. I asked her about a certain statement that sounded too certain for the circumstances described.
So I give a brief overview of Popper's falsification, etc and the examples that I always go to on that subject; namely how often the theories of early Earth change, but yet each theory is always presented with such certainty.
Wikipedia's timeline has: