In a groundbreaking discovery, U.S. scientists have uncovered the oldest directly dated ice and air ever found on Earth in the Allan Hills region of East Antarctica — ice that dates back six million years. The finding provides an extraordinary window into a time when the planet was significantly warmer and sea levels were far higher than today.
The study, published in the Proceedings of the National Academy of Sciences (PNAS), was led by Sarah Shackleton of the Woods Hole Oceanographic Institution and John Higgins of Princeton University, as part of the Center for Oldest Ice Exploration (COLDEX) — a National Science Foundation-funded collaboration of 15 U.S. research institutions led by Oregon State University (OSU).
“Ice cores are like time machines that let scientists look back at what our planet was like in the past,” said Shackleton. “The Allan Hills cores take us much further back in time than we ever thought possible.”
COLDEX Director Ed Brook, a paleoclimatologist at OSU, called the discovery the project’s most significant achievement so far.
“We knew this ice was ancient, but we only hoped to find ice up to three million years old. Discovering samples twice that age is beyond our wildest expectations,” Brook said.
While other international teams have drilled continuous ice cores up to 1.2 million years old deep in Antarctica’s interior, COLDEX researchers explored a different approach. They worked on the edges of the East Antarctic ice sheet, drilling only 100–200 meters deep where a combination of rugged topography, fierce winds, and extreme cold helps preserve ancient ice close to the surface.
“We’re still learning how such old ice can survive near the surface,” Shackleton explained. “It’s probably a mix of cold temperatures and persistent winds that strip away newer snow, leaving ancient layers exposed — though it also makes Allan Hills one of the harshest places on Earth to work.”
Using argon isotope analysis, scientists were able to directly date the ice — a rare achievement in paleoclimate research. These samples represent “climate snapshots” up to six times older than any previous ice core data.
Preliminary results show that the Allan Hills region has cooled by about 12°C (22°F) over the past six million years, marking the first direct measurement of long-term Antarctic temperature decline. Researchers are now analyzing trapped air bubbles to reconstruct ancient greenhouse gas levels and ocean heat content, offering valuable insights into how natural climate systems respond to global warming.
Brook said COLDEX teams will return to Allan Hills in the coming months to drill deeper and search for even older ice.
“This discovery opens up a new chapter in Antarctic exploration,” he said. “Between 2026 and 2031, we plan an extensive study to push the boundaries of our understanding of Earth’s ancient climate.”
Collaborating Institutions: Oregon State University, Princeton University, Woods Hole Oceanographic Institution, University of Washington, Scripps Institution of Oceanography (UC San Diego), University of Maine, Tongji University (China), and University of Minnesota.
Funding: The research was supported by the National Science Foundation (NSF) through its Office of Polar Programs, Science and Technology Center Program, and the U.S. Antarctic Program, with ice drilling support from the NSF U.S. Ice Drilling Program and sample curation by the NSF Ice Core Facility in Denver, Colorado.
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