In a remote region of East Antarctica, among the Allan Hills, researchers have extracted an ice core reaching back six million years—the oldest ice ever directly dated, along with the air trapped within it. The find offers rare access to an era when the planet was noticeably warmer, sea levels were significantly higher, and the atmosphere contained very different concentrations of greenhouse gases.
The study was led by Sarah Shackleton of the Woods Hole Oceanographic Institution and John Higgins of Princeton University, working as part of the COLDEX Center for Oldest Ice Exploration. This initiative brings together fifteen American research institutions under the leadership of Oregon State University. The scientists worked at a field camp located at an altitude of two thousand meters, where boreholes only one hundred to two hundred meters deep allowed access to the oldest layers. Thanks to the unique interaction between glacial flow and the terrain—steep mountains and gorges—the ancient layers here are closer to the surface and more accessible for study than in the center of the ice sheet, where they would have to be retrieved from depths exceeding two thousand meters.
Direct dating was made possible by directly measuring the isotopic composition of argon in air bubbles. This method, unlike indirect approaches, does not require assumptions about continuous stratification of the ice and provides confidence in the age of the samples. The study, published in the journal Proceedings of the National Academy of Sciences, showed that the ice from the Allan Hills is six times older than the previous record for continuous ice cores, which was eight hundred thousand years.
Analysis of oxygen isotopes in the ice itself revealed a dramatic picture: the region cooled gradually but steadily—by about twelve degrees Celsius—over the entire six-million-year period. This is the first direct measurement of such long-term cooling in Antarctica over such a vast timespan. At the same time, the ice samples allow reconstruction of greenhouse gas concentrations in the atmosphere of that ancient era—the Miocene and Pliocene periods, when Earth's climate was substantially different from today.
Unlike continuous records from the last eight hundred thousand years, the obtained samples represent not a continuous chronicle but discrete 'snapshots' of climate—fragments separated by layers of younger ice. However, it is precisely this fragmentation that expands the scientific horizon: it allows a glimpse into eras about which previously one could only speculate. COLDEX director Ed Brook, a paleoclimatologist at Oregon State University, noted that the find far exceeded expectations: scientists had hoped to discover ice up to three million years old, but found samples twice as ancient.
In the context of global science, COLDEX is one of several teams engaged in a friendly competition to push the boundaries of ice archives. A European group recently announced the discovery of a continuous core reaching 1,2 million years, but the find in the Allan Hills shifts the timescale back several million years—albeit in the form of individual fragments rather than a continuous column.
In the coming years, the COLDEX team plans new expeditions to the Allan Hills area. The goal is ambitious: to obtain even older samples and more detailed 'climate snapshots' that can be assembled into a single mosaic. The work is scheduled for the period from 2026 to 2031 and could significantly expand understanding of natural climate variability and the mechanisms that govern the evolution of the Earth system.
Such findings remind us of the fragility of the planetary climate system. Direct evidence from the depths of time is not just a symbol of past eras but a genuine key to understanding modern changes. When we see how climate has changed over millions of years, it becomes possible to assess the scale and speed of changes occurring today and to anticipate where they might lead.
