Dear PF Forum, I have questions about carbon based life and molecule back bone. Is it true that all life on earth are carbon based? If it is true, why? Is it because carbon is halfway in periodic table? 4 valence? What about Silicon, Tin and Germanium? They have 4 valence, why life is not based on them? Is it because Carbon the simplest atom then Silicon, Tin and Germanium? Why polymer backbone are mostly carbon? Can polymer be constructed from silicon, tin and germanium? Perhaps these are too many questions for one thread, my point is all these questions lead to carbon based life. Is carbon based life because of all of those question? Thanks for explaning to me. Steven.