Why can't we see evidence of alien life? - Chris Anderson

 

Stand by for an animated exploration of the famous Fermi Paradox. Given the vast number of planets in the universe, many much older than Earth, why haven't we yet seen obvious signs of alien life? The potential answers to this question are numerous and intriguing, alarming and hopeful.
http://ed.ted.com/lessons/questions-no-one-knows-the-answers-to
Lesson by Chris Anderson, animation by Andrew Park.