Researchers have discovered the oldest directly dated ice and air samples on Earth, dating back 6 million years, in the Allan Hills region of East Antarctica. This breakthrough provides unprecedented insights into the planet's ancient climate and atmosphere. The finding, detailed in a recent study, reveals a significant cooling trend over millions of years.
In a major advance for paleoclimatology, a team led by Sarah Shackleton of the Woods Hole Oceanographic Institution and John Higgins of Princeton University identified 6-million-year-old ice in the Allan Hills area of East Antarctica. The samples, containing trapped air bubbles, offer the oldest direct record of Earth's atmosphere. Published on October 28 in the Proceedings of the National Academy of Sciences, the study highlights how this ice preserves fragments of climate history far beyond previous records.
The discovery stems from efforts by the Center for Oldest Ice Exploration (COLDEX), a National Science Foundation-funded initiative established in 2021 and coordinated by Oregon State University. COLDEX aims to extend ice core records past the prior 800,000-year limit. While a European project recently achieved a 1.2-million-year continuous core, the Allan Hills samples push the timeline to 6 million years, though in discrete pieces rather than a continuous sequence.
"Ice cores are like time machines that let scientists take a look at what our planet was like in the past," Shackleton explained. The team drilled 100 to 200 meters into the ice near the Antarctic ice sheet's edge, where wind and cold preserve ancient ice close to the surface. Ages were determined using argon isotope measurements, confirming the samples' antiquity without relying on sediments.
Analysis shows the region cooled by about 12 degrees Celsius (22 degrees Fahrenheit) over 6 million years, the first direct quantification of this shift from a warmer era with higher sea levels. Ed Brook, COLDEX director at Oregon State University, called it the center's most important find, exceeding hopes of 3-million-year-old ice.
Future work will analyze greenhouse gases in the bubbles and includes a new expedition to Allan Hills, with plans for extended studies from 2026 to 2031. Contributors include researchers from Oregon State, Princeton, University of Washington, Scripps Institution of Oceanography, University of Maine, Tongji University, and University of Minnesota. The project is supported by NSF's Office of Polar Programs and related programs, with field operations aided by the U.S. Antarctic Program.