With the late Professor Sir Nicholas Shackleton in charge, the focus of research shifted to marine isotope records, which document changes in the size of polar ice sheets and temperature changes. This research helped to establish the Milankovitch Theory as the most plausible explanation of glacial/interglacial changes over the past million years, and was continued to develop much more extensive geological timescales, covering the last 30 million years, on the basis of this hypothesis. Other areas researched by members of the laboratory include pollen records and tree rings as a proxy for past climate. The laboratory changed principal allegiance from the Department of Plant Sciences to the Department of Earth Sciences around 1995.