In a research by paleoceanographer Andre Bornemann of Leipzig University in Germany and his colleagues analyzed apparently unaltered Foraminifera picked from sediment core drilled from Demerara Rise beneath the western equatorial Atlantic. Following a classic technique, the researchers measured oxygen isotopes in the forams' shells. They found a sharp shift toward the heavier oxygen-18 isotope in both surface and bottom dwelling forams from 91.2 million years ago.