The tundra biome has an average temperature of -28 degrees Fahrenheit and can drop as low as -70 degrees. It is characterized by permanently frozen soil called permafrost that extends over 450 meters deep. Though cold, the ocean helps regulate temperatures from becoming too extreme. The tundra covers 10% of the Earth's surface and is home to herbivores like caribou and lemmings, and carnivores such as arctic foxes and polar bears that hunt them.