When was pot first smoked?

Answer 1

It is not certain exactly when people started smoking marijuana. Undoubtedly, it was in prehistory. Marijuana has been found buried with cavemen. For a good history, see Marijuana, The First 12,000 Years

http://druglibrary.org/schaffer/hemp/history/first12000/abel.htm

Answer 2

Marijuana can be traced back to ancient religious celebrations to ward off demons and cleanse the soul, approximately 30,000 BC. This is however unconfirmed by any hard evidence, just stories and artifacts that have been found throughout the world.