The biosphere is the final of the four earth spheres that we will examine in this course. The biosphere is a complex, interactive system of abiotic (nonliving) and biotic (living) components that interact with the atmosphere, hydrosphere and lithosphere. Our first topic of discussion, soils, is the link between the lithosphere and the plants that cover our earth and interact with the atmosphere and the hydrosphere. Plants play an essential role in the development of soils, and they are the foundation of all earth ecosystems. Large, terrestrial ecosystems that are characterized by specific plant communities and formations are termed biomes. These biomes are the foundation of the biosphere and a key to understanding the vitality of all earth systems.