He continues to study stromatolites. Recently, he has begun studying Neoproterozoic deposits in eastern California. In 2003, he, Frank Corsetti and David Pierce published evidence in the Proceedings of the National Academy of Sciences of fossilized microbiota in Cryogenian rocks, a revelation which has cast doubt on the notion of the near elimination of life during potential equatorial glaciation during that period (commonly referred to as Snowball Earth).[7]