Earth is home to more than 30 million different kinds of living things, some of which are still being discovered. This realm of life is called the biosphere. the biosphere is the shell of life that extends downward about 5 miles (8 kilometers) into the deep ocean basins and porous lithosphere rock and extends upward about 5 miles (8 kilometers) to the mountaintops. It is the most dynamic and fragile realm in a complex system of interacting spheres that make up the planet.