ENVIRONMENT

the complex of physical, chemical, and biotic factors that act upon an organism or an ecological community and ultimately determine its form and survival. The Earth's environment is treated in a number of articles. The major components of the physical environment are discussed in the articles atmosphere, climate, continental landform, hydrosphere, and ocean. The relationship between the principal systems and components of the environment, and the major ecosystems of the Earth are treated in the article biosphere. The significant environmental changes that have occurred during Earth's history are surveyed in the article geochronology. The pollution of the environment and the conservation of its natural resources are treated in the article conservation. Hazards to life in the biosphere are discussed in the articles death, disease, and immune system.