Uncle Joe tells his nephew Mark that if he quits smoking for one year, he will give him $10000. Mark agreed and stopped smoking. After one year elapsed with Mark not smoking - he informed uncle Joe and then asked for the money. Uncle Joe congratulated Mark but refused to pay him the $10000 he promised. Mark sues Uncle Joe claiming breach of contract. Uncle Joe argues that Mark did not give any consideration - thus the contract is not enforceable.

Is this anenforceable contract? Why or why not?