It includes between 3 and 30 million species of plants, animals, and fungi, and also two kinds of single-celled living things: those without nuclei ("prokaryotes") such as bacteria, and those with nuclei ("eukaryotes") such as protozoans. The biosphere extends over the Earth's surface in a thin layer from a few kilometers into the atmosphere, in very cold environments, to the deep-sea vents of the ocean depths, in very hot environments.

(U.S. Fish & Wildlife Service/J & K Hollingsworth)

The biosphere is a life-supporting global ecosystem, where each living things depends on each other and the environment. The ecosystem includes all living organisms and the abiotic or nonliving environment on which they depend for their energy and the nutrients they need to live.

(U.S. Fish and Wildlife Service/Bruce Batten)

(U.S. Fish and Wildlife Service/J.D. Pittillo)