This document describes the four spheres that make up Earth's systems - the hydrosphere, atmosphere, geosphere, and biosphere. It provides details on each sphere, including that the hydrosphere is made up of 71% of Earth's surface as oceans and saltwater, while the atmosphere is a thin gaseous envelope composed of nitrogen, oxygen, water vapor and aerosols. The document also notes that the geosphere encompasses Earth's solid interior from the crust to the core, and the biosphere incorporates all living things on the planet.