The majpr systems of the earth are atmosphere, biosphere, hydrosphere and lithosphere. Subsystems would be things like of the hydrosphere the water cycle ie ocean water evaporating and forming clouds and then passing over mountains and precipitating as fresh water and then having run-off forming creeks and rivers and then returning to the sea. A subsystem of the lithosphere would be the rock cycle of how sediments are transported and deposited and converted to sedimentary rock and then perhaps heated and with pressure become metamorphic rocks and then the movement of the tectonic plates and subduction would result in igneous rocks being formed,