Are we alone in the universe? The one question that fascinates me more than any other. And my perspectives are these. The sheer complexity of biological forms makes me think that the evolution of intelligent life forms (such as humans) is likely to be a rather sparse occurrence. There will be many Earth-like planets … perhaps at least millions in the outer arms of the Milky Way revolving around stars like the Sun that the Earth revolves around. But the temperatures have to be just right for water to be plentiful in all three states. What were the stuff available in the early Earth that created the conditions that led to the emergence of primitive life forms? A planet with a lot of volcanic activity, lot of carbon-based complex organic molecules, a planet with continental plates slowly drifting, pushing, merging, separating, rising, and falling, lots of lightning, etc. How many planets will have all these enablers? Reduces the candidate planets to perhaps thousands. Then on pl...