The Drake equation is an awesome educational tool. It leads you to think thoughts like this: The Earth is 4.6 billion years old. Prokaryotic life is currently

The Drake equation is an awesome educational tool. It leads you to think thoughts like this: The Earth is 4.6 billion years old. Prokaryotic life is currently estimated to have formed 3.5 to 4.5 billion years ago -- not really that long after Earth formed. Now consider: Extrapolating from a few photos taken by the Hubble Ultra Deep Field camera, scientists currently think that there are on the order of hundreds of billions of galaxies in the universe. Ours is an average galaxy, with about 200 billion stars. That implies that there are at least 10^22 stars in the universe. In other words: For every single second that the Earth has been in existence, there are about 70,000 stars in the universe. Maybe more. So it's not exactly difficult to believe that life, however rare it may be, probably exists in at least two places in the universe. Though we may well never know for sure.