An ice sheet is a mass of glacial land ice larger than 50,000 square kilometers, and Earth has just two of them: one covering most of Greenland and one across Antarctica. As of November 2026, the Antarctic Ice Sheet holds about 30 million cubic kilometers of ice, while the Greenland Ice Sheet holds about 2.9 million. Each year a new layer of snow falls on the ice sheets of Greenland and Antarctica, and because summer snow differs from winter snow in chemistry and texture, each layer records that year.

Scientists drill long cores out of ice sheets, and some of these cores are more than 3,500 meters (11,000 feet) deep. They hold hundreds of thousands of years of snow layers. Scientists began drilling long ice cores in Greenland and Antarctica in the late 1960s. By the early 1990s the Greenland project had pulled a core of 3,053.44 meters, covering at least 110,000 years, and Antarctic cores reach back about 750,000 years. As snow falls it also traps dust, volcanic ash, smoke and pollen, and what is trapped tells scientists about the conditions when the snow formed. Scientists use volcanic ash found in ice cores to date the cores and to estimate how strong past volcanic eruptions were.

The hole left by an ice core is useful too. Scientists lower a thermometer into the borehole to measure the temperature of the ice sheet directly, because snow and ice, like an insulated thermos, preserve the temperature of each layer. The ice that holds these records is not still. Near the top of an ice sheet, where the slope is shallowest, ice moves a few centimeters to a few meters per year, but near the coast, ice flowing into outlet glaciers can move hundreds of meters or even several kilometers per year. Ice shelves are floating sheets of ice that are connected to the land, and Antarctic ice shelves can break off icebergs more than 80 kilometers (50 miles) long.

Less than 1 percent of Antarctica is free of ice. It has towering mountain ranges, ice-free dry valleys with ancient rocks and fossils, and active volcanoes. Around it lies the Southern Ocean, the water around Antarctica. The United States recognizes it as reaching from the Antarctic coast to 60 degrees South, but not all countries agree on its edge. The Antarctic Convergence is an uneven line where cold water flowing north from Antarctica meets the warmer waters of the world's oceans, and it marks the edge of the Antarctic region. The Southern Ocean also connects all of the world's oceans and carries nutrients across the globe, and temperature differences between the poles and other regions keep these ocean currents moving. Six kinds of seal live in the waters around Antarctica.

Life in these cold waters has its own tools. Antarctic fish have natural antifreeze in their blood, called glycoproteins, that stops it from freezing, and the icefish has no red blood cells and carries oxygen in its blood plasma. Emperor penguins keep warm in several ways. Their layered, scale-like feathers shrug off winds over about 110 kilometers per hour, and they have small bills and flippers and blood vessels that warm and cool blood to save heat. Emperor penguin fathers keep the single egg warm on their feet for about two months, without eating. Antarctic krill are small, shrimp-like animals that most of the larger animals in the region eat, and leopard seals eat penguins and other seals.

People came to this ice as discoverers and then as scientists. Roald Amundsen was the first to reach the South Pole, in December 1911, and Robert F. Scott arrived in January 1912. The US South Pole station is named for both men. As of November 2026, the South Pole station is at 90 degrees South and drifts about 10 meters (33 feet) each year because the ice it sits on moves. In 1959, 12 countries signed the Antarctic Treaty, which sets Antarctica aside for peaceful science and freezes territorial claims, so no new claims can be made while it is in force. Antarctica has no native people, but scientists and other people live and work at research stations there.

Words to know

• glycoproteins: antifreeze molecules
• borehole: drilled hole
• convergence: meeting line
• plasma: blood liquid