Researchers studying ice cores from central Greenland have identified fossilized plant and insect material buried beneath roughly three kilometers of ice, evidence that the island’s interior was ice-free at least once within the past 1.1 million years. The discovery, published in 2024 in the Proceedings of the National Academy of Sciences, suggests that the Greenland ice sheet has been less stable over long timescales than previously assumed.

The material came from sediment samples collected in 1993 by the Greenland Ice Sheet Project 2 (GISP2), a drilling operation at Summit, the highest and thickest point of the ice sheet. The drill extracted a continuous ice core more than 3,000 meters long, and crews continued into the underlying rock and sediment. Those basal samples were stored in a facility in Colorado and largely forgotten for about three decades.

Recent re-examination of the samples revealed willow wood, a poppy seed, spike moss, fungal remains, and insect fragments. The assemblage points to an Arctic tundra environment rather than a forest. The plants and organisms once lived on open, rocky ground during a warm interglacial period before ice returned to cover the site.

To determine when that landscape existed, scientists used cosmogenic nuclide dating, which measures the accumulation of beryllium-10 and aluminum-26 in rocks exposed at the surface. The ratio of these isotopes indicated that the Summit area had been ice-free at least once in the last 1.1 million years, during a period when early humans were already dispersing across the globe.

The findings align with earlier work from a separate location. Camp Century, a U.S. military base built inside the ice sheet in northwestern Greenland in the late 1950s, produced basal sediments in 1966 that were later shipped to Denmark and left in storage. Researchers rediscovered those frozen samples around 2017.

Analysis of that material found intact twigs and leaves beneath more than a kilometer of ice. A 2021 study in the Proceedings of the National Academy of Sciences reported that northwestern Greenland was ice-free during at least two warm intervals within the past million years. A subsequent 2023 study in Science led by Andrew Christ of the University of Vermont used luminescence dating, which measures how long mineral grains have been shielded from sunlight, to determine that the Camp Century site was ice-free about 400,000 years ago during a notably long warm period known as Marine Isotope Stage 11.

Modeling combined with those results suggested that the loss of Greenland ice during that period contributed to more than one meter of global sea-level rise. Atmospheric carbon dioxide levels at the time were significantly lower than today.

Earlier genetic evidence had pointed in the same direction. In 2007, a team led by Danish researchers reported in Science that DNA extracted from basal ice at a site called Dye-3 in southern Greenland indicated the presence of a boreal forest with spruce, pine, beetles, and butterflies, dating to between roughly 450,000 and 800,000 years ago.

Greenland’s bedrock, mapped by radar surveys from aircraft, also reveals a landscape that predates the ice sheet. A 2013 study in Science described a canyon buried beneath the ice, stretching at least 750 kilometers from the interior toward the northern coast. It is longer than the Grand Canyon and is believed to have been carved by flowing water before the ice sheet formed.

Radar data from NASA’s Operation IceBridge and other surveys have built a detailed picture of the terrain below the ice, including mountains near the coast, deep basins, and the ancient channel.

The fossils do not indicate that the entire ice sheet disappeared at any single point, but the evidence from Summit, near the center of the island, is significant. If the thickest part of the ice sheet melted away during a past warm period, then the current ice sheet may be more sensitive to warming than the image of a permanent frozen dome suggests.

The full melting of the Greenland ice sheet would raise global sea levels by roughly seven meters, or about 23 feet. That process would unfold over centuries or millennia depending on the scale of future warming, but satellite measurements show that Greenland is already losing hundreds of billions of tons of ice per year on average in recent decades, making it a major contributor to observed sea-level rise.

For scientists, the value of the fossils lies in testing computer models used to project future ice-sheet behavior. If a model cannot reproduce an ice-free Greenland under past conditions that are now known to have produced one, it may not reliably predict what will happen as the climate warms.

The preserved plants and organisms, some small enough to fit on a fingertip, represent data points from earlier warm periods. They show that the island’s environment has changed dramatically before, and they provide a benchmark for understanding how it may respond to current and future changes in the climate system.