AP BIOLOGY

Detailed explanation-1: -Permafrost is a permanently frozen layer on or under Earth’s surface. It consists of soil, gravel, and sand, usually bound together by ice. Permafrost usually remains at or below 0°C (32ºF) for at least two years. Permafrost can be found on land and below the ocean floor.

Detailed explanation-2: -Permafrost is found in places where the average annual temperature is below about 23°F (-5° C), including most of the Arctic and all of Antarctica. Land with underlying permafrost is called tundra.

Detailed explanation-3: -The “permanence” of permafrost depends on the length of seasonal freeze-thaw cycles. In Arctic tundra freeze-thaw cycles, winters are long and summers are short. The active layer of permafrost, the topmost layer of soil, thaws in the summer and freezes in the winter.