On another occasion, I mentioned a review of Wielenberg's "In Defense of Non-Natural, Non-Theistic Moral Realism", ( Faith and Philosophy 29:1 (2009), pp. 23-41) in Philosopher's Digest. Here is a link to Wielenberg's paper itself. The paper offers an undercutting defeater for claims made by Copan, Craig, Moreland, et al. that atheism can't provide an adequate meta-ethical basis for morality.