POLAR BIOME

plant and animal community of either the Arctic or the Antarctic region, characterized by a cold, arid climate and a perpetual cover of snow or ice. Despite similarities of latitude, temperature, and barrenness, the Arctic and the Antarctic polar regions have markedly different plant and animal communities. In both regions, the year is divided about equally between day (summer) and night (winter) owing to the continuous position of the Sun above or below the horizon during these seasons. The polar ice caps are about 4.5 million years old. It is probable, based on fossil discoveries, that before the ice froze over the poles, both polar regions had temperate climates and were covered with forests. Variations in world climate and the poleward drift of landmasses have, over millions of years, rendered the Arctic and Antarctic largely barren, with only about 10 mm (0.4 inch) of yearly rainfall and permanently frozen subsoils. What flora exists is due to snowmelt and the sunlight of the long summer day. At the North Pole is the Arctic Ocean, lying in the midst of islands and landmasses (the northernmost being Greenland) and the Canadian arctic archipelago. In all lowland areas the extreme cold is relieved with above-freezing temperatures for a month or more each year, allowing for a varied plant and animal life. The South Pole is occupied by the continent of Antarctica, the mountains of which project through the world's greatest ice cap. No more than about 4 percent of the Antarctic's land is capable of sustaining life, while only the coast of Graham Land on the Antarctic Peninsula and several off-lying islands are warmed each year by above-freezing temperatures.