The solid portion of the earth. It is also known as the lithosphere. From a technical standpoint, the geosphere includes inner parts of the earth virtually inaccessible to human study, the inner and outer core and mantle, as well as the outermost crust. For the most part, however, environmental scientists are primarily interested in the relatively thin outer layer of the crust on which plants and animals live, in the ores and minerals that occur within the crust, and in the changes that take place in the crust as a result of erosion and mountain-building.