Generally defined, the portion of the universe where all life is found is called the biosphere. Since scientists have not found organisms beyond planet Earth, the biosphere is defined as the parts of Earth where life exists. The biosphere is made of three parts, called the lithosphere, atmosphere and hydrosphere. Some portions of each may not support life, however; for example, the upper regions of the atmosphere do not support life, while the lower regions do. This general definition of the biosphere is commonly accepted, although geologists sometimes define the biosphere more narrowly to include only the life itself - the bacteria, algae, plants and animals, including humans, that inhabit the earth, instead of their environments. Under these more narrow definitions, the biosphere forms a fourth part of the Earth system and interacts with the other three.
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The biosphere is the portion of Earth where life occurs -- the portions of the land, water and air that hold life. These parts are known, respectively, as the lithosphere, hydrosphere and atmosphere. The lithosphere is the land mass, excluding Earth’s mantle and core, which do not support life. The hydrosphere is the aquatic portion of the planet, all of which supports life. The atmosphere is the air that living organisms use for respiration, and which supports life up to 2,000 meters above the planet’s surface.
The lithosphere is the terrestrial part of the biosphere. It consists of the solid land masses, such as continents and islands. The deeper parts of the lithosphere, known as the lower mantle and the core, do not support life. The rest of the lithosphere supports a variety of life from bacteria to large mammals and trees hundreds of feet tall. The weathering of the lithosphere crust forms soil, which provides minerals and organic waste to support life. In addition, the land provides shelter and protection for animals from weather and predators, and an anchor for plants.
The hydrosphere is the aquatic part of the biosphere. This includes oceans, rivers, lakes and other bodies of water. Unlike the lithosphere and the atmosphere, every portion of the hydrosphere supports life. Specially-adapted bacteria grow in hot springs, tube worms form the basis of sulfur-based communities around deep-sea, hydrothermal vents, and in more hospitable regions, life abounds. Water-dwelling individuals of virtually every taxonomic group of plants and animals have been identified as important parts of the biosphere. Water is essential to life, and the hydrosphere also plays an important part in atmosphere formation.
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The atmosphere is the gaseous envelope surrounding a planet. On Earth, it is also called air. The lower regions of the atmosphere contain gases such as oxygen and carbon dioxide that are essential for plant and animal respiration. Birds, insects and other life can be found up to approximately 2,000 meters above the earth's surface. The atmosphere also plays critical roles in shaping the biosphere by deflecting harmful radiation from the sun and determining weather patterns