We shall limit our observations to the conditions in natural ecosystems, since it would be beyond the scope of this book to embark upon a consideration of secondary, man-made ecosystems. 2. Classification of the Geo-biosphere into Zonobiomes The biosphere is the thin layer of the earth's surface to which the phenomena connected with living matter are confined. On land, this comprises the lowest layer of the atmosphere permanently inhabited by living organisms and into which plants extend, as well as the root-containing portion of the lithosphere, which we term the soil. Living organisms are...