1. the portion of the earth comprising the lower atmosphere, the seas, and the land surface (mantle rock) in which living organisms exist 2. the part (reservoir) of the global carbon cycle that includes living organisms (plants and animals) and life derived organic matter (litter, detritus) —note the terrestrial biosphere includes the living biota (plants and animals) and the litter and soil organic matter on land; the marine biosphere includes the biota and detritus in the oceansThis definition last updated 10/24/2008