Answer: There are five main systems, or spheres, on Earth. The first system, the geosphere, consists of the interior and surface of Earth, both of which are made up of rocks. The limited part of the planet that can support living things comprises the second system; these regions are referred to as the biosphere. In the third system are the areas of Earth that are covered with enormous amounts of water, called the hydrosphere. The atmosphere is the fourth system, and it is an envelope of gas that keeps the planet warm and provides oxygen for breathing and carbon dioxide for photosynthesis. Finally, there is the fifth system, which contains huge quantities of ice at the poles and elsewhere, constituting the cryosphere. All five of these enormous and complex systems interact with one another to maintain the Earth as we know it.
