Archaean atmosphere and climate

Abstract

Arising from: H. Ohmoto, Y. Watanabe & K. Kumazawa Nature 429, 395–399 (2004); see also communication from N. H. Sleep; H. Ohmoto & Y. Watanabe replyOhmoto et al.1 argue that carbon dioxide was abundant in the late Archaean and early Proterozoic atmosphere and that methane was probably scarce, based on a reanalysis of the occurrence of siderite, FeCO3, in ancient rocks. Here I consider several factors that may undermine their conclusions.