Oregon State University–led researchers report recovering ice and trapped air from Antarctica’s Allan Hills that date to about 6 million years, a result published in the Proceedings of the National Academy of Sciences. The finding greatly exceeds COLDEX’s initial target (~3 million years) and the previous ice-core record (~800,000 years). The samples formed during a warmer, higher-sea-level interval and will help refine reconstructions of ancient climate and atmospheric composition. The team plans to return to Allan Hills to drill additional holes and search for even older ice.
OSU-Led Team Recovers ~6-Million-Year-Old Ice and Trapped Air from Antarctica’s Allan Hills
Oregon State University–led researchers report recovering ice and trapped air from Antarctica’s Allan Hills that date to about 6 million years, a result published in the Proceedings of the National Academy of Sciences. The finding greatly exceeds COLDEX’s initial target (~3 million years) and the previous ice-core record (~800,000 years). The samples formed during a warmer, higher-sea-level interval and will help refine reconstructions of ancient climate and atmospheric composition. The team plans to return to Allan Hills to drill additional holes and search for even older ice.
12:28, 02.11.2025Science
OSU-led team finds oldest-known ice and atmospheric samples — about 6 million years old
PORTLAND, Ore. — A research team led by Oregon State University reports it has recovered ice and air bubbles believed to be the oldest directly sampled on Earth. The international effort, coordinated through OSU’s Center for Oldest Ice Exploration (COLDEX), extracted material estimated at roughly 6 million years old from the Allan Hills region of Antarctica.
Princeton’s John Higgins and Sarah Shackleton of the Woods Hole Oceanographic Institution helped lead the field campaign that recovered the samples. The results were published this week in the Proceedings of the National Academy of Sciences and represent COLDEX’s most significant finding since the center was established in 2021.
“We’re still working out the exact conditions that allow such ancient ice to survive so close to the surface,” Shackleton said. She noted that a combination of local topography, persistent strong winds that remove fresh snow, and extremely cold temperatures that nearly halt ice flow likely keep very old ice shallow at Allan Hills. That mix makes the site one of the best places to find shallow, ancient ice — and one of the toughest places to carry out a field season.
How the team worked and why it matters
Over several months, researchers drilled boreholes as deep as 200 meters to reach and sample the oldest ice. The recovered ice and entrapped air formed during a period when multiple lines of geological evidence indicate warmer global temperatures and higher sea levels than present. The trapped air offers a rare opportunity to directly measure ancient atmospheric composition and improve reconstructions of past climate and sea-level change.
COLDEX researchers say the new samples far exceed previous ice-core age records (about 800,000 years) and surpass the team’s initial target of roughly three million years. Scientists worldwide have expressed interest in locating and dating still older ice, and the team plans to return to Allan Hills to drill additional holes and refine their age estimates and climate interpretations.
Next steps
The researchers will perform detailed laboratory analyses of the ice and the trapped gases to extract temperature, greenhouse gas, and sea-level information from the mid-Pliocene and late Miocene intervals represented by these samples. Those data could help test climate models and improve our understanding of Earth’s sensitivity to greenhouse gas forcing.