Extension to the extension.

I think another important question is the amount of known history where there were planets that could support life. This gives us an idea of how much of a head start some other species, given perfect evolutionary conditions, could have on us. We can then use our history of the cosmos to determine at what points in the life of the universe the most life-supporting planets arose. This also would help us understand what percentage of other civilizations are more advanced than us and to what degree.