Before you read this, please watch the first two minutes of this video:
Then allow me to de-construct a couple of the arguments of, and generally get a little angry at, the guy with the cross on his cap:
"Don't you guys believe there's no such thing as god? Therefore... there's no purpose to life!"
Wow. Did he really say that? Yeah I think he did... And unfortunately, if you're an Atheist (like me) you'll hear this quite frequently from a lot of different people. Some of them are even quite intelligent most of the time. So why do they still ask this question? God only knows... ;)
The idea that there is a purpose to life is a matter of personal opinion, and it needn't (although it almost always is) be affected by the person's religion, or lack thereof. I personally believe there IS a purpose to life, but I don't know yet what it is. I often think it might be solely to reproduce, until many generations down the line, when Humans are more evolved a global purpose develops. Sometimes I think it is to make the most of our lives individually and to help others make the most of theirs, but I find it hard to see the whole-species goal in simply 'living a full life'. So I don't have an answer, but that by no means is to say that there isn't one! The pursuit of the meaning of life is a good enough purpose in itself, until the meaning is found, so to simply be content with the purpose of your life being some part of an unseen, unheard and unknown being's master plan for the universe while you sit bit and let it all wash over you with no intention to search for the truth seems a entirely wasteful way to live your life, to me!
"So 100 years from now, nothing we ever did or said or believed is going to matter, because once we die, we cease to exist? Am I right?"
No you definitely are NOT right. Our life ends when we die, so we, as a functioning human body and brain do cease to be alive, but our EXISTENCE lives on through memories of others who knew us who are still alive, and the stories of us that they tell to their relatives, through the actions that we have taken which affect the world after we're gone, such as donating organs to save the lives of others, or through creating a business or idea or form of entertainment that people can enjoy after our death. Of course we affect the world, everyone does! If anything, a belief in the afterlife only serves to lessen the likelihood that you will do anything worth remembering in this life, because it's too easy to sit back, live a 'good' life and look forward to your cushy eternity in heaven.