Earth's Plate Tectonic Climate Control
One of the most astonishing chapters in Earth’s history is “Snowball Earth”: The twice entombing of the whole planet beneath a kilometer-thick layer of ice for tens of millions of years. More improbable still is that the end of the last episode around 635 million years ago somehow helped to spark the rise of the diversity of complex animals and land plants along with the high atmospheric oxygen levels that define the modern world. Surprises were not, however, limited to the biosphere. Through the snowball episodes, Earth’s average global climate switched sharply in character from a relatively warm and ice-free world of the previous billion years (the boring billion) to one akin to present day, marked by glacial cycles, dynamic ice sheets and profound climate variability of varying intensity over time scales ranging from years to millions of years. How did Earth’s climate become so cold after being warm for so long? Why did consequent global glaciations persist for tens of millions of years and why were there two episodes? What triggered snowball Earth in the first place and how did Earth eventually escape this climatic death sentence? Why is Earth’s current climate so nervous—so sensitive to, for example, anthropogenic sources of CO2. In work that develops a new view of the dynamics of “the Earth System”, we show how effects of plate tectonics on Earth’s mantle convective stirring, including the intermittent formation and fragmentation of supercontinents, modulates the major volcanic and weathering controls on Earth’s average climate, setting the stage for protracted periods of warmth, for variability akin to present day and for snowball Earth.