1. The Earth can be understood as a system consisting of interconnected subsystems - the geosphere, hydrosphere, atmosphere, and biosphere.
2. The geosphere includes the solid Earth from the crust to the core. The hydrosphere is the dynamic mass of water on Earth. The atmosphere is the thin gaseous layer surrounding the planet. The biosphere includes all ecosystems and life forms on Earth.
3. These subsystems interact through material cycles like the carbon, water, and rock cycles. They exchange heat and energy. Together they comprise the closed Earth system, which receives energy from the sun.