6-Million-Year-Old Ice Found in Antarctica Yields Oldest Trapped Air, Opening Window on Earth’s Ancient Climate
Researchers from the Center for Oldest Ice Exploration (COLDEX) recovered ice and trapped air from Allan Hills, East Antarctica, dated about 6 million years — the oldest directly dated ice and air, opening a crucial window into ancient climate.
- Oldest directly dated air and ice: Tiny bubbles in Allan Hills samples are ~6 million years old — a record for directly dated trapped atmosphere.
- Direct dating via noble gases: Argon isotope measurements dated the ice itself, strengthening confidence that the gases are ancient.
- Long-term cooling recorded: Oxygen isotopes indicate roughly a 12°C (~22°F) cooling in the Allan Hills over 6 million years.
- Snapshots of warmer worlds: Discontinuous Allan Hills samples provide time slices up to six times older than continuous Antarctic cores, informing sea-level and ice-sheet behavior.
Discovery and what makes it record-setting
Where it was found: The COLDEX team drilled and sampled ice exposed in the Allan Hills region of East Antarctica, where glacier dynamics bring very old ice close to the surface. Because these samples are exposed and discontinuous, researchers accessed very old ice without multi-kilometer deep drilling.
Those recovered samples contain tiny, unmixed air bubbles. Measuring noble gases in those bubbles demonstrated that they did not mix with the modern atmosphere for about 6 million years, making them the oldest directly dated trapped air on record.
“The Allan Hills samples recovered by COLDEX provide the oldest directly dated ice and trapped air yet recovered on Earth.”
How the ice was dated and analyzed
Dating ancient ice is challenging. COLDEX used high-precision mass spectrometry to measure argon isotopes — including argon-40 — and other noble gases trapped in the bubbles. This direct-dating method gives an age for the ice itself rather than relying on surrounding sediments or indirect proxies, increasing confidence that atmospheric gases measured are truly ancient.
Parallel oxygen isotope analysis of the ice provides a temperature proxy: those ratios point to a long-term cooling in the Allan Hills region of roughly 12°C (22°F) over the past 6 million years, covering the end of the Miocene into the Pliocene epochs.
Primary publication: Results and methods are detailed in a study published in the Proceedings of the National Academy of Sciences (PNAS).
What the trapped air can tell us
The frozen bubbles are miniature atmosphere samples from ~6 million years ago. By measuring greenhouse gases such as carbon dioxide and methane in these bubbles, scientists can track natural variability of greenhouse-gas concentrations during much warmer intervals long before human industrial activity.
Why that matters: Those measurements will help benchmark climate models by providing direct comparisons of natural greenhouse-gas and temperature relationships during periods with higher global temperatures and higher sea levels.
Snapshots, not a continuous timeline — why that matters
Allan Hills samples are discontinuous snapshots rather than a continuous core. Each sample provides a time slice that can be much older than continuous Antarctic cores, giving access to ancient climate intervals previously out of reach — including parts of the Pliocene often used as analogues for future warming.
These snapshots complement continuous cores: together they extend the temporal reach of paleoclimate records and allow targeted study of specific warm intervals and sea-level events.
Evidence of a very different Antarctica
Combined with geological records, the ice data support a view that Antarctica was once much warmer and may have supported forests before large, persistent ice sheets formed. The new measurements show a multi-million-year transition from warmer, forested landscapes toward the heavy glaciation that dominates today — a central record for understanding how ice sheets grow and shrink.
Tools, team and next steps
Team: COLDEX is a U.S. collaboration led by Oregon State University involving 15 institutions. Key scientists named in coverage include Sarah Shackleton (Woods Hole Oceanographic Institution) and John Higgins (Princeton University).
Methods: The work relied on precision mass spectrometry for argon isotopes and oxygen isotope analysis to reconstruct temperatures.
Next steps: COLDEX plans further drilling in Allan Hills between 2026 and 2031 to target even older ice and to expand the snapshot record. Deeper analyses of trapped gases and links to ocean heat content are already underway.
Scientific significance and broader meaning
By setting records for the oldest dated ice and trapped air, this discovery widens the historical range scientists can study and provides direct evidence of natural greenhouse-gas levels and temperature during much warmer periods. That makes Allan Hills samples an important benchmark for testing climate models and refining projections of ice-sheet response to future warming.
Implications for the United States
Economic impact: Findings about past sea levels and ice-sheet behavior could affect coastal planning, insurance risk calculations, and federal infrastructure spending. If ancient warm periods show faster ice loss than expected, coastal states may face higher costs for flood defenses and insurance.
Political consequences: More precise paleoclimate data can inform debates in Washington and state capitals on infrastructure investments, disaster preparedness, and federal support for rural and coastal communities. Robust evidence can guide targeted, evidence-based spending decisions.
Social effects: Rural communities that depend on stable seasons for planting and harvests can use improved long-term climate information to prepare for shifts in growing seasons, water availability, and extreme events—without one-size-fits-all mandates.
Practical applications: Federal and state agencies, extension services, and local planners can use refined models based on this ancient record to prioritize projects protecting roads, levees, water systems, and coastal facilities.
Cultural relevance: Framing these findings as tools for stewardship and local resilience connects national research to the values and priorities of many rural Americans.
Sources and further reading
- Oregon State University news release
- Space.com coverage
- University of Maine Climate Change blog
- PNAS research article
- Nautilus feature
- IFLScience coverage
Researchers at COLDEX and partner institutions will continue drilling and analyzing these rare samples to build a clearer picture of Earth’s ancient climate and the lessons it holds for communities across the United States.
