Deep in East Antarctica, scientists have recovered ice containing tiny pockets of air that remained sealed foraround 6 million years. These samples are now the oldest directly dated ice ever collected on Earth and are giving researchers an unusually clear look at what the planet’s atmosphere was like millions of years ago.
The discovery comes from the Allan Hills region, where an international team analyzed the cores and published its findings in 2025 in Proceedings of the National Academy of Sciences. The results went far beyond what the researchers had expected to find.
The research team reported that the ice extends the climate archive much further than previously directly dated ice discoveries, opening access to a period of Earth’s history that remains difficult to explore.
Tiny Bubbles Trapped Ancient Air
The recovered material was not simply frozen water. Embedded within the ice were microscopic bubbles containing ancient air that had remained isolated for millions of years. As detailed in Proceedings of the National Academy of Sciences, researchers studied chemical isotopes preserved inside those air pockets to reconstruct environmental conditions from that distant period.
Sarah Shackleton, one of the lead researchers at Woods Hole Oceanographic Institution, described the value of the discovery in a statement:
“Ice cores are like time machines that let scientists take a look at what our planet was like in the past. The Allan Hills cores help us travel much further back than we imagined possible.”
Back in the laboratory, the team measured the chemical signatures preserved in the trapped air and identified evidence showing that the region cooled by around 12°C (22°F) over the last 6 million years. The researchers noted that the finding matches previous evidence suggesting Earth was warmer during that time.
Allan Hills Exposed Old Ice
Recovering ancient Antarctic ice usually requires drilling deep beneath the surface. In other parts of East Antarctica, extracting continuous records often means reaching depths greater than 2,000 meters (6,561 feet). At Allan Hills, the situation turned out to be very different.
The team drilledbetween 100 and 200 meters (328 to 656 feet) below the surface and recovered long cylindrical samples cores. Researchers explained that local geography appears to have played a major role. Mountain terrain combined with slow-moving ice gradually pushed much older layers upward, bringing them closer to the surface than normal. They are still trying to fully understand why such old ice survived there.
Shackleton said a combination of strong winds and persistent cold likely contributed, adding that:
“Along with the topography, it’s likely a mix of strong winds and bitter cold. The wind blows away fresh snow, and the cold slows the ice to almost a standstill.”
She also described Allan Hills as one of the best places in the world to search for shallow ancient ice and, at the same time, one of the most challenging places to work.
The Team Expected Old Ice, But Not This Old
Researchers entered the project believing they had chosen a promising location, though the final result still surprised them. Ed Brook, Director of COLDEX and paleoclimatologist at Oregon State University, said the original goal was to find ice dating back around 3 million years, perhaps slightly older.
“We knew the ice was old in this region. Initially, we had hoped to find ice up to 3 million years old, or maybe a little older, but this discovery has far exceeded our expectations,” he explained in a statement published by Oregon State University Newsroom.
John Higgins of Princeton University said the project has created a collection of “climate snapshots” stretching roughly six times older than previously reported ice-core data while complementing younger Antarctic records.
Brook also said the discovery has already led the team to prepare a broader study of the Allan Hills region.
“Given the spectacularly old ice we have discovered at Allan Hills, we also have designed a comprehensive longer-term new study of this region to try to extend the records even further in time, which we hope to conduct between 2026 and 2031.”
Enjoyed this article? Subscribe to our free newsletter for engaging stories, exclusive content, and the latest news.
