6 Million-Year-Old Ice Found in Allan Hills Shatters Records — Ancient Air Trapped Inside Offers New Look at Earth’s Climate Past
Researchers in East Antarctica’s Allan Hills have recovered the oldest directly dated ice on Earth — about six million years old — offering a direct window into Pliocene climates, ancient atmosphere samples, and a long-term Antarctic cooling trend.
- Oldest directly dated ice: shallow core from Allan Hills dated to ~six million years, a record age for directly dated ice.
- New dating method: direct measurement of an argon isotope trapped in air bubbles reduces age uncertainty.
- Climate signal: oxygen isotopes show ~12 °C Antarctic cooling across the six-million-year span and evidence of warmer Pliocene intervals.
- Policy relevance: trapped ancient air and long-term records can inform models, infrastructure planning, and national strategy.
The discovery
A multi-institution U.S. team working under the Center for Oldest Ice Exploration (COLDEX) recovered a shallow ice core in the Allan Hills region of East Antarctica that dates to roughly six million years — far older than the three million years the team expected. The Allan Hills site is unique because local ice flow and geology expose very old ice nearer the surface, allowing access without the extreme deep drilling used on the central Antarctic plateau.
The work was led by researchers including Sarah Shackleton of the Woods Hole Oceanographic Institution and John Higgins of Princeton University, with participation from 15 research centers and funding from the National Science Foundation. The discovery was announced in October 2025 and published in peer-reviewed summary materials from the research teams. See the WHOI press release and a university summary of the ice-core analysis at the University of Maine climate summary.
Dating methods and precision
What distinguishes this find is the direct dating. Instead of relying on stratigraphic inference, the team measured an isotope of the noble gas argon trapped in tiny air bubbles inside the ice to obtain an age for the ice itself. This argon-isotope technique is a major methodological advance, offering greater confidence in timelines that pair atmospheric composition and temperature proxies from the same, directly dated layers.
“Direct measurement of argon isotopes in trapped air reduces several uncertainties associated with indirect dating and strengthens paleoclimate timelines,” said COLDEX researchers in public summaries.
Climate insights from 6 million years ago
Preliminary oxygen-isotope analyses from Allan Hills indicate a clear, long-term cooling trend across the six-million-year span. Researchers report Antarctic temperatures dropped by roughly 12 °C (about 22 °F) over that interval — the first direct, long-term Antarctic temperature measurement from ice rather than indirect geologic proxies.
Chemical and geological signatures in the ice also record warmer intervals during the Pliocene era, when global temperatures and sea levels were higher. The trapped air bubbles are particularly valuable: they retain ancient greenhouse gas concentrations and other atmospheric markers that, when paired with isotopic temperature proxies, create multi-layered climate snapshots useful for understanding rates and drivers of past change.
Research goals and future work
Scientists plan to analyze both the trapped air and the ice chemistry to reconstruct greenhouse gas levels, ocean heat content, and other variables over multimillion-year timescales. The Allan Hills result is being treated as a starting point: COLDEX teams will return for further drilling, and a multi-year study led by Oregon State University and funded by the NSF is planned for 2026–2031 to expand the record and search for even older ice.
Ed Brook, COLDEX director and paleoclimatologist at Oregon State, said the team has “designed a comprehensive longer-term new study of this region to try to extend the records even further in time,” with work envisioned between 2026 and 2031. For details, see the WHOI press release.
Implications for the United States
The Allan Hills discovery has several practical implications:
- Economic and scientific leadership: It underscores U.S. leadership in paleoclimate research and the value of sustained NSF-funded field science and instrumentation.
- Energy and policy decisions: Longer-term natural climate context can improve models used to evaluate future risks and economic trade-offs — helping craft pragmatic strategies balancing growth, security, and resilience. See the University of Maine climate summary for discussion of policy relevance.
- Agriculture and infrastructure planning: Deeper records can refine risk assessments for coasts, farms, and water systems and inform investments in coastal defenses, storage, and flood control.
- National security and global posture: Extended climate baselines help military and intelligence planners develop scenarios related to migration, food security, and resource stress.
- Public debate and policy balance: The find provides neutral scientific evidence on natural long-term variability alongside ancient greenhouse-gas data, supporting measured, evidence-based decisions.
Practical takeaways for communities include updated hazard maps, building-code revisions in vulnerable areas, and prioritization of investments that protect lives and livelihoods based on clearer long-term risk assessments.
Sources and attribution
Key reporting and public summaries include the WHOI press release and a university climate summary at the University of Maine climate site. These sources provide the primary public-facing details of the COLDEX discovery and preliminary analyses.
Preserved URLs: WHOI press release — University of Maine climate summary.
