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: -If you dig down through the arctic tundra, you’ll soon strike a rock-like layer of frozen soil. Even on the warmest summer day, this permafrost layer lies anywhere from a few inches to a few feet below the tundra surface, never thawing. About 85% of Alaska’s land area is underlain by permafrost.

Detailed explanation-3: -Permafrost is soil, rock or sediment that is frozen for more than two consecutive years. In areas not covered by ice, it exists beneath a layer of soil, rock or sediment, which freezes and thaws annually and is called the “active layer".

Detailed explanation-4: -The upper surface of permafrost is called the permafrost table. In permafrost areas the surface layer of ground that freezes in the winter (seasonally frozen ground) and thaws in summer is called the active layer.

Detailed explanation-5: -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.