I don't know how to forward it, but I saw another article posted by francopoli stating that life may be more rare than previously believed because phosphorus is not as plentiful as previously believed. It's interesting how we seem to get very different messages from science (and other sources) about the same topic.
Here is the discussion thread. We were talking about what possible alternatives to phosphorus are for alien biology. I see your point, but would point out that this article is discussing similarity among bodies within one solar system, which makes sense as we all condensed out of the same planetary disk. The other article is highlighting dissimilarity between solar systems due to location. The makeup of planetary disks seems to differ based on what kinds of stellar explosions contributed to them. This also makes sense. Now I am wondering if the answer to Fermi is that the universe is only just now becoming capable of making planets with enough elements for complex life?
I saw that today just before posting this comment which clarifies a lot. You explained the issue better than I did. I realize it's sort of apples to oranges since Venus was exposed to the same elements Earth was at formation and other solar systems might be different because of what they were or were not exposed to. My understanding is that our solar system is in a less crowded area of the Milky Way, on a spiral arm. One would think that stars in more crowded regions were exposed to more. Maybe it's sort of like Earth in that there are deserts, savannahs, rainforests, etc. with different potentials.
That's probably the reason aliens haven't made contact with us yet. We're so far out in the boonies, we're not seen as worth the effort. Sucks to be them though. They don't know the party they're missing.My understanding is that our solar system is in a less crowded area of the Milky Way, on a spiral arm.