One interesting possibility that doesn't seem to get discussed much is metallicity. Stars containing more heavy elements tend to be younger, while older stars t

One interesting possibility that doesn't seem to get discussed much is metallicity. Stars containing more heavy elements tend to be younger, while older stars tend to have a lower metallicity. Looking at our own biochemistry, you don't just need carbon, nitrogen, oxygen, and hydrogen to make it work. Heavier elements from the fourth and fifth periods of the periodic table are also required. I wouldn't be surprised if life is rare but also becoming more common over the last few billion years. Evolution also doesn't necessarily lead to intelligent life capable of harnessing technology.