Scientists have found complex microbial life deep below the Earth's surface, in sediments and rocks under the ocean and continents. These microorganisms are different from those on the surface and can live as deep as 1 km below the seafloor and 3 km in the continent. The deep biosphere may make up half of the Earth's biomass. Researchers are studying this hidden world to learn more about its diversity and how it impacts the global biosphere.