If there is no God, then all that exists is time and chance acting on matter. If this is true then the difference between your thoughts and mine correspond to the difference between shaking up a bottle of Mountain Dew and a bottle of Dr. Pepper. You simply fizz atheistically and I fizz theistically. This means that you do not hold to atheism because it is true , but rather because of a series of chemical reactions . . . . Morality, tragedy, and sorrow are equally evanescent. They are all empty sensations created by the chemical reactions of the brain, in turn created by too much pizza the night before. If there is no God, then all abstractions are chemical epiphenomena, like swamp gas over fetid water. This means that we have no reason for assigning truth and falsity to the chemical fizz we call reasoning or right and wrong to the irrational reaction we call morality. If no God, mankind is a set of bi-pedal carbon units of mostly water. And nothing else.
From a debate between Farrell Till and Douglas Wilson. See the transcript here.