Scientists have discovered the oldest directly dated ice in the Allan Hills region of East Antarctica -A piece of "ice pimple" formed about 6 million years ago, which also contains prehistoric air. This breakthrough discovery was completed by the "Center for the Exploration of the Oldest Ice" (COLDEX) team funded by the US National Science Foundation. The relevant results were published in the "Proceedings of the National Academy of Sciences" on November 3, 2025.
The Allen Hills are located on the edge of the Antarctic ice sheet. The movement of ice flow and the rugged mountain terrain work together to lift the ancient ice layers near the surface, avoiding the high pressure and deformation deep in the ice sheet.
The research team directly determined the age of the ice layer by analyzing the ratio of argon isotopes trapped in the ice. This method breaks through the limitations of traditional ice cores that rely on sediments to infer age, with an error of only ±100,000 years.
Previously, the world's oldest continuous ice core record was 800,000 years old, but this discovery extends the time span by six times!
Analysis of oxygen isotopes in ice shows that Antarctica has experienced a long-term cooling of about 12°C in the past 6 million years. This is the first time humans have directly quantified the temperature evolution of the Antarctic continent from the late Miocene to the Pliocene, providing key data for understanding the ice sheet expansion mechanism.
Preliminary analysis of air bubbles in ice suggests thatThe carbon dioxide concentration in the late Pliocene (about 6 million years ago) was about 270-300 ppm, which was significantly lower than the 425 ppm inferred from sediment cores., challenging the traditional understanding that "high carbon dioxide drives Pliocene warming".
The research also revealed a slight drop in carbon dioxide levels about 2.7 million years ago, which coincides with the time when Earth entered the 100,000-year ice age cycle.