Final answer:
Ice sheets are massive formations of glacial ice covering vast areas, such as the Greenland ice sheet. These ice sheets contain vital clues about Earth's climatic past and present changes and are studied in locations like Glacier National Park in the USA.
Step-by-step explanation:
Ice sheets are enormous masses of glacial ice covering over 50,000 square kilometers. For example, the Greenland ice sheet is an immense body of ice, roughly a thousand kilometers wide, with intriguing features such as cells or polygons averaging over 30 kilometers in width. The middle of these ice sheets often contains massive blocks of frozen water ice, with some reaching incredible heights of 2 to 3 kilometers. These ice formations play a significant role in Earth's climate and are studied to understand past and present geological and environmental changes.
In the case of Glacier National Park (GNP) in Montana, USA, glaciers from the last glaciation, which ended about 12,000 years ago, carved the park's majestic peaks. The current smaller alpine glaciers formed around 7,000 years ago and expanded substantially during the Little Ice Age (LIA). At the end of the LIA around 1850 AD, the park housed over 150 glaciers, as evidenced by aerial photography of moraines. Today, fewer than 30 active named glaciers remain in GNP.
Glacial cycles have repeatedly occurred throughout history, sometimes reaching as far south as 40° latitude in the northern hemisphere. This dynamic process of glacier formation and retreat is governed by climatic factors, such as temperature and precipitation.