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The Phanerozoic carbon-isotopic record (central panel) from marine carbonates. Peripheral panels A–D show expanded views of intervals containing notable carbon-isotopic variability and/or carbon isotope excursions. Carbon isotope excursions are generally associated with geologic events such as volcanic eruptions, episodes of anoxia, and extinctions. And, for the most part, carbon isotope excursions have been interpreted as directly arising from such individual environmental perturbations. Yet, their ubiquity, and generally declining amplitude through time raise the possibility of a common underlying control. On page 641 Bachan and others offer a framework for linking recurrent environmental forcing (such as sea-level changes) to the carbon-isotopic record through episodic contraction and expansion of shallow-marine anoxia. Viewed from this perspective, carbon isotope excursions arise from a combination of external environmental forcing and internal carbon cycle amplification, and the decline in their amplitude over time is indicative of an overall stabilization of the Earth System.