I like the exercise of extrapolating from the history of life on Earth to get an idea of how likely life is to develop elsewhere. Life on Earth likely appeared very soon after the surface cooled enough for liquid water. It was so soon that it seems like single cell life might be downright common in any place with stable liquid water.
On the other hand, it took billions of years for complex multi-cellular life to evolve. The Cambrian explosion was just 541 million years ago and quickly resulted in intelligence on branches as disparate as mammals and cephalopods.
I think it's quite possible that the Cambrian is the rare and special thing and that the universe may be teaming with microbes but not fish.
On the other hand, it took billions of years for complex multi-cellular life to evolve. The Cambrian explosion was just 541 million years ago and quickly resulted in intelligence on branches as disparate as mammals and cephalopods.
I think it's quite possible that the Cambrian is the rare and special thing and that the universe may be teaming with microbes but not fish.