The atheist's motivation stems from a general compassion for his or her own species, which because of evolution and natural selection, he or she innately wishes to protect and nurture, to cause to grow and become a visibly better or more cohesive brotherhood, which can be accomplished through the employment of ethical standards.
The idea that there needs to be some intangible "afterlife" reward in order for people to care about our present state of existence is preposterous, and little more than a veiled form of bribery, which ironically is viewed as an evil in most forms of organized religion. There is no logical reason why we should have any reason to believe that after death, one experiences consciousness -- we have never identified a single credible person who could provide any sort of evidence of this concept's truth. Yet, we do know what it's like to experience absolute lack of consciousness -- people who've experienced comas, or being knocked out by traumatic brain injury almost universally correlate the experience to a timeless, formless, dreamless, lack of any self-awareness.
Judging by the fact that death also involves a lack of brain function, it stands to reason that the most likely scenario for what occurs after death is most akin to unconsciousness; a total non-existence of thought or perception. Not black or white or any color, because we lack any thought to conceive of these concepts.
