The Earth's natural systems can be divided into five major subsystems or "circles": the atmospheric system, the land surface system, the oceanic system, the ice system, and the biological system.

In the scientific community, the Earth's climate system is generally believed to be composed of these five subsystems.

One of these subsystems is the ecosystem, abbreviated as ECO. It refers to the unified whole of organisms and their environment within a certain natural space. Organisms and the environment interact with each other, leading to a relatively stable dynamic equilibrium over time. The solar system is an ecosystem, with the sun acting as an engine that provides constant energy to it.

In a broader sense, natural systems include ecological balance systems, living organism systems, celestial systems, material microstructure systems, and social systems, among others. In the natural world, the circulation and evolution of material flow are crucial.

There is no end to the natural environmental system, only a cycle that repeats and develops from one level to another. All life on Earth depends on these complex and vast natural systems, which are formed by various natural forces interlocking with each other.

The biosphere is the largest ecosystem on Earth, while the tropical rainforest ecosystem is the most complex. Humans primarily live in artificial ecosystems, mainly cities and farmland. Ecosystems are open systems that require constant input of energy to maintain their stability, otherwise, they are in danger of collapse.

Many substances constantly cycle in ecosystems, with the carbon cycle closely related to the global greenhouse effect. Ecosystems are a major structural and functional unit in the field of ecology, belonging to the highest level of ecological research.

The components of an ecosystem include abiotic matter and energy, producers, consumers, and decomposers. Among these, producers are the main components. Different types of ecosystems include forest, grassland, marine, freshwater (such as lake, pond, and river ecosystems), farmland, tundra, wetland, and urban ecosystems.

The inorganic environment is the basis of an ecosystem, and its condition directly determines the complexity of the ecosystem and the richness of the biological communities within it. Organisms and the environment are inseparable, forming a whole that we call an ecosystem.

With the development of ecology, ecologists believe that organisms and the environment should be studied as an inviolable whole. E.P. Odum proposed that ecology should be defined as "the science of the structure and function of ecosystems," studying the species, number, biomass, life history, and spatial distribution of organisms within a certain area.

His theory greatly influenced the teaching and research of ecology in universities, and he was awarded the Taylor Ecology Prize, the highest honor in ecology in the United States. He was also the first person to propose the concept of an ecosystem.