it's like winning a lottery. although the odds are astronomical, most weeks someone hits the jackpot. but there is another intriguing idea called panspermia, which says life could have generated somewhere else and been spread from planet to planet by asteroids. >> larry: dr. kaku, in your opinion, how did it all start? >> probably on the earth. probably in the oceans where there's liquid water. we physicists always say follow the water. liquid water is the amniotic fluid of life where dna got off the ground. >> larry: isn't water redundant? >> ice is actually quite common out of space. comets are made out of water. liquid water is the most precious substance. we have a lot of it on earth. >> larry: why here and why then? because there was water? >> and we think that water is the mixing bowl for dna getting