Twenty thousand years ago, in the thick of an Ice Age, Earth looked very different. Because water was locked up in glaciers hundreds of feet thick, which stretched down over Chicago and New York City, the ocean was smaller—shorelines extended hundreds of miles farther out, and the remaining water was saltier and colder.
A University of Chicago scientist led a study that recently announced the discovery of the first-ever direct remnants of that ocean: pockets of seawater dating to the Ice Age, tucked inside rock formations in the middle of the Indian Ocean.
“Previously, all we had to go on to reconstruct seawater from the last Ice Age were indirect clues, like fossil corals and chemical signatures from sediments on the seafloor,” said Clara Blättler, an assistant professor of geophysical sciences at the University of Chicago, who studies Earth history using isotope geochemistry. “But from all indications, it looks pretty clear we now have an actual piece of this 20,000-year-old ocean.”
Blättler and the team made the discovery on a months-long scientific mission exploring the limestone deposits that form the Maldives, a set of tiny islands in the middle of the Indian Ocean. The ship, the JOIDES Resolution, is specifically built for ocean science and is equipped with a drill that can extract cores of rock over a mile long from up to three miles beneath the seafloor. Then scientists either vacuum out the water or use a hydraulic press to squeeze the water out of the sediments.