Glaciers are relics of Earth’s past yet incredibly relevant to its present and future. Glaciers, ice caps, and related forms of land ice can be up to a million years old, and they hold nearly 70% of the world’s fresh water. The largest glacier, Antarctica's Seller Glacier, is 7,000 square kilometers in area alone. Scientists estimate that if all of Earth’s land ice were to melt, it would raise global sea level by 70 meters. 

Glaciers typically begin to form when snow falls in mountainous areas, transforms to ice that does not completely melt away in summer, and adds new layers each winter. As glaciers grow, gravity begins to pull them down into the valleys below. Some glaciers become large enough to form dome-shaped masses of ice that spread out in all directions; these are known as ice caps (less than 50,000 square kilometers) and ice sheets (more than 50,000 kilometers).

Glaciers are enormously important to track and study because they shape Earth's terrain, provide water and nutrients to ecosystems and communities, influence and regulate weather and climate, and contribute to global sea level rise. NASA has many datasets to help researchers and resource managers characterize glacier evolution and makeup.