Using the "#arseniclife" controversy as a case study, we examine the roles of blogs and Twitter in post-publication review. The controversy was initiated by a scientific article about bacteria able to substitute arsenic for phosphorus in its genetic material. We present the debate chronologically, using prominent online media to reconstruct the events. Using tweets that discussed the controversy, we conducted quantitative sentiment analysis to examine skeptical and non-skeptical tones on Twitter. Critiques of and studies refuting the arsenic life hypothesis were publicized on blogs before formal publication in traditional academic spaces and were shared on Twitter, influencing issue salience among a range of audiences. This case exemplifies the role of new media in informal post-publication peer review, which can complement traditional peer review processes. The implications drawn from this case study for future conduct and transparency of both formal and informal peer review are discussed.