Atheism and Neuroscience
Thanks to neuroscience, we know that the destruction of a part of one's brain can fundamentally change who we are in terms of personality and character. Thus, our personality and character are inextricably expressed through the form of our brain. Since our brain decays after our death, we cannot possibly have an afterlife in the Christian sense, i.e. our individual personalities will not last. If some spiritual part of, say, Joe Schmo, does last it will be so different than the Joe Schmo that we know (and that Joe himself knows) that he would not longer be recognizable as Joe Schmo. Of course, a theist could always believe that there is biological death but "then a miracle happens" and your personality is retained as part of your soul in the afterlife.