Biologists have classified the terrestrial (land) portion of the biosphere into biomes-large regions such as forests, deserts, and grasslands, with distinct climates and certain species (especially vegetation) adapted to them. Figure 3-6 shows different major biomes along the 39th parallel spanning the United States (see Figure 5 on p. S 19 in Supplement 4 for a map of the major biomes of North America).
Scientists divide the watery parts of the biosphere into aquatic life zones, each containing numerous ecosystems. There are freshwater life zones (such as lakes and streams) and ocean or marine life zones (such as coral reefs, coastal estuaries, and the deep ocean). The earth is mostly a water planet with saltwater and freshwater life zones covering almost three-fourths of its surface.
生物學家已經把從生物圈到大地區的生物群系的陸地部分，以不同氣候型態且某些物種特別是植物適應其氣候型態加以分類，例如森林、沙漠和草原。圖3-6顯示各種主要的生物群落分部沿著橫越美國的北緯39度線。
科學家把從生物圈到水生生物區的水域加以劃分，每一個包含許多生態系統。有淡水的生物區域(例如湖泊和小溪河流以及遠洋或者海洋生物區域(例如珊瑚礁，沿海河口和深海)。地球主要是由海水和淡水的生物區域以及包括將近它的表面的4分之3的組成的一顆水行星。
