In the far-northern regions of the world, and in isolated regions in the Antarctic, there are thousands of miles of barren plains known as tundra. These regions have an extremely low average temperature, and a very short summer season. The primary characteristic of the tundra is a layer of permanently frozen soil known as permafrost just below the topsoil layer, which prevents many plants from taking root and making agriculture all but impossible. Like deserts, the tundra receives little precipitation; however, the flat, frozen ground keeps groundwater from draining, forming bogs where various grasses, moss, and other simple vegetation can grow. Despite the harsh environment, a wide variety of animal life flourishes in the tundra, providing possible sources of food, and providing trade potential for the fur and trapping industry.