Final answer:
Ice sheets are massive continental glaciers covering over 50,000 square kilometers, with the Antarctica and Greenland ice sheets being the largest. These ice sheets hold most of Earth's fresh water, impacting global climate and sea levels.
Step-by-step explanation:
The enormous continental masses of glacial ice covering over 50,000 square kilometers are referred to as ice sheets. The most notable ice sheets on Earth today are the Antarctic ice sheet and the Greenland ice sheet. These massive ice sheets contain the majority of the world's fresh water and have significant impacts on the global climate. For example, the Greenland ice sheet holds roughly 2.85 times as much ice as the polar ice caps on Mars, which is an interesting comparison even though they are about the same to the nearest power of 10. Antarctica's ice is even more extensive; about 90% of the Earth's ice volume is in the Antarctic ice sheet.
Antarctica's Ross Ice Shelf is a source of gargantuan icebergs such as the one that broke away in 1986, measuring 160 km long and 40 km wide. Beneath the Antarctic ice sheet are sub-glacial lakes like Lake Vostok, which is the size of Lake Ontario. Should all the ice and snow be removed from the continent, the land area would be much smaller, comprising mainly of mountain ranges and islands. Additionally, the melting of this ice would contribute to a global rise in sea levels.