For several million years, the Earth cycled through ice ages at a regular pace, but then, 1.25 million to 700,000 years ago, something changed: ice ages went from lasting 40,000 years to 100,000. … By looking at the microscopic shells of microorganisms called foraminifera, Adam Hasenfratz of the Geological Institute in Zürich, Switzerland, and colleagues, find evidence of a reduction in deep water circulation, causing less carbon dioxide to be released into the air. Oceanic changes in the Antarctic Zone could have ensured “that glacial conditions persisted despite orbital changes to the contrary”, the study says. The new research, presented...