Proterozoic climate dynamics, including both remarkable climate stability during the mid-Proterozoic and extreme low-latitude glaciation in the Neoproterozoic, must be understood in the framework of evolving oxidant reservoirs throughout the Precambrian. We present Earth system model simulations showing that recent constraints on atmospheric oxygen and oceanic sulfate during Proterozoic time have profound implications for marine methane cycling and the accumulation of methane in the atmosphere. Our model results challenge the paradigm of persistently elevated methane during the Precambrian, thus extending the relevance of the faint young Sun paradox throughout the Proterozoic. In light of the possibility of low methane during the mid-Proterozoic, we also suggest a conceptual model for the relationship between oxygenation, methane, and Neoproterozoic Snowball Earth events.

Abstract