The Neoproterozoic Era, which lasted from 1,000 million to 542 million years ago, was a time of dramatic change on Earth. Continents moved into and out of a supercontinent, life evolved to be increasingly complex and two ice ages covered the entire globe in ice. The atomic weight of carbon in limestone rocks that formed in Neoproterozoic oceans, known as isotopic data, has been used to argue for large changes in the global movement of carbon through Earth’s surface environment. However, interpretations that these isotopic data record a global, rather than local, process requires showing the same signal from rocks on multiple continents. Global correlations have been proposed, but are difficult to test because precise age determination of the rocks requires the presence of relatively rare volcanic ashes within the limestones. New research in northern Ethiopia led to the discovery of such volcanic ashes within a stack of sedimentary rocks known as the Tambien Group. These ashes were precisely dated and are combined with new data on the physical relationship of the rocks and their carbon isotopic composition developed by an international team of researchers from the US, the UK and Ethiopia. Comparison with data from a pile of sedimentary rocks and a dated ash in northwest Canada provides a positive test of the correlation of high magnitude carbon isotope change approximately 800 million years ago. This research, combined with other ongoing efforts, promises to strengthen understanding of the timing and pace of the significant global change that dramatically changed Earth’s surface during Neoproterozoic time.