Environment refers to the thin layer of life and life supports called the biosphere, including the earth’s air, soil, water, and living organisms. The atmosphere that shelters the earth from excessive amounts of ultraviolet radiation and enables life to exist is a gaseous mixture of nitrogen, oxygen, hydrogen, carbon dioxide, water vapor, other elements and com pounds, and dust particles. Heated by the sun and by radiant energy from the earth, the atmosphere circulates about the planet and modifies temperature differences. Of the earth’s water, 93 to 97 percent makes up the oceans, 2 percent is ice, and 1 percent is the fresh water in rivers, lakes, groundwater, and atmospheric and soil moisture. The soil is the thin man tie of material such as glacial till and sedimentary rocks, and vegetation. Dependent on all these are the earth’s living or ganisms, including humans. Plant use water, carbon dioxide, and sunlight to convert raw materials into carbohydrates through photosynthesis. Animal life, in turn, is dependent on plants. The species Homo Sapiens -- this is humanity -- appeared late in the earth’s history but was ultimately able to modify the earth's environment by its activities. Although humans apparently first appeared in Africa, they quickly spread throughout the world. Because of their unique mental and physical capabilities, humans were able to escape the environ mental constraints that limited other species and to change the environment to meet their needs. Although early humans undoubtedly lived in some harmony with the environment, as did other animals, changes in human relationships with the environment and their retreat from the wilderness began with the first, prehistoric agricultural revolution. The ability to control and use fire permitted them to modify or eliminate natural vegetation, and the domestication and herding of grazing animals resulted in overgrazing and soil erosion. The domestication of plants also promoted destruction of natural vegetation to make room for crops, and the demand for wood for fuel and to build cities and ships denuded mountains. Wild animals were slaughtered for food and destroyed as pests and predators. While human populations remained small and technology modest, human impact on the environment was localized. As populations increased and technology improved and expanded, however, problems arose. In fact, environmental problems have plagued humans and the earth since the dawn of written history. With the Industrial Revolution, humans began in ear nest to change the face of the earth, the nature of its atmosphere, the quantity and quality of its water. Today, unprece dented demands on the environment from a rapidly expanding human population and from advancing technology are causing a continuing and accelerating decline in the quality of the environment and its ability to sustain life. The ingredient of atmosphere does NOT include ______.