I don't understand the assumption purposed in the headline and the introduction. First of all, atheists are not nihilists. Second, why would a life be more meaningful if there is an afterlife than if there isn't? If anything life should be more meaningful without an afterlife. Because then you can live your life and take it for what it is, instead of dreaming about afterlife, thinking of this life as a chore that you must to do to get the compensation. Seriously, I have a friend who can't wait to die, because he wants to see what's next. How is he living a more meaningful life?

Life's meaning should be derived from the life itself instead of what does or doesn't follow it.