Chyba (2005) reviews an article by Tian et al. (2005) that suggests that the loss of hydrogen from the Earth's early atmosphere was two orders of magnitude slower than previously thought. Abundance of hydrogen and products of volcanic outgassing would have produced an environment more favorable for life than alternative pathways in an atmosphere with lower hydrogen abundance.
References
Chyba, C. F., 2005: Rethinking Earth's early atmosphere. Science, 308, 962.
Tian, F., O.B. Toon, A.A. Pavlov, and H. De Sterck, 2005: A hydrogen-rich early Earth atmosphere. Science, 308, 1014-1017.