6-Million-Year-Old Antarctic Ice Found — Oldest Directly Dated Ice Reveals Ancient Air and Climate

6-Million-Year-Old Antarctic Ice Found — Oldest Directly Dated Ice Reveals Ancient Air and Climate

Researchers have recovered a block of Antarctic ice that dates to about 6 million years ago, making it the oldest directly dated ice sample ever retrieved. The discovery, described in a study published Oct. 28 in the journal PNAS, gives scientists access to ancient air and climate records from the Miocene epoch.

“Ice cores are like time machines that let scientists take a look at what our planet was like in the past,” said Sarah Shackleton, lead author of the study, a researcher at Princeton University and an assistant scientist at the Woods Hole Oceanographic Institution. “The Allan Hills cores help us travel much further back than we imagined possible.”

The record-setting ice and the air trapped inside it are more than twice as old as previously known directly dated samples (about 2.7 million years). The ice was recovered from the Allan Hills blue-ice area in East Antarctica during field seasons between 2019 and 2023. The Allan Hills ice field lies at roughly 6,500 feet (2,000 meters) above sea level.

To collect the samples, teams drilled 330–660 feet (100–200 meters) into the ice. Scientists dated the ice by measuring the radioactive decay of argon isotopes trapped in air bubbles — a direct technique for determining the age of enclosed air — and analyzed oxygen isotopes in the ice itself. Those oxygen isotope data indicate the Allan Hills region has cooled by roughly 22°F (12°C) over the last 6 million years.

Because the ice contains ancient air, it can reveal past concentrations of greenhouse gases and past ocean temperatures. These records help researchers separate long-term natural climate drivers from the rapid, human-driven warming caused by modern greenhouse-gas emissions, improving climate models and our understanding of Earth’s climate sensitivity.

The persistence of such old ice close to the surface appears to result from a combination of local conditions: near-static surface ice flow, rugged mountainous topography that traps ice, strong katabatic winds that scour away new snowfall, and persistently frigid temperatures that slow ice flow. Together, these factors make Allan Hills one of the rare places on Earth where shallow, ancient ice survives and is accessible to field teams — albeit in a logistically challenging environment.

“We’re still working out the exact conditions that allow such ancient ice to survive so close to the surface,” Shackleton said. “Along with the topography, it’s likely a mix of strong winds and bitter cold. That makes Allan Hills one of the best — and toughest — places in the world to find shallow, old ice.”

Implications: The discovery extends the direct ice-and-atmosphere record into the Miocene, offering a new window on Earth when global temperatures and sea levels were higher. That deeper baseline strengthens scientists’ ability to place modern warming in long-term context and to test models of ice-sheet and climate response.