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The Bushmen have left over 20,000 individual rock paintings, all preserved in caves at more than 500 different sites. (read more)

Featured Article: Dolmen

Poulnabrone dolmen in County Clare, Ireland
A Dolmen (also known as cromlech, anta, H√ľnengrab, Hunebed, quoit, and portal dolmen) is a type of single-chamber megalithic tomb, usually consisting of three or more upright stones (megaliths) supporting a large flat horizontal capstone (table). Most date from the early Neolithic period (4000 B.C.E. to 3000 B.C.E.). Dolmens were usually covered with earth or smaller stones to form a barrow, though in many cases that covering has weathered away, leaving only the stone 'skeleton' of the burial mound intact.

Found in many parts of the world, the numerous still standing dolmens provide an opportunity to understand the values and beliefs of those who lived long ago. Their widespread appearance attests to a certain universality in human nature, particularly with regard to death and burial. They are evidence that even early cultures had the desire and ability to transport and place these enormous stones. Requiring great planning, coordination, and collaboration for their construction, dolmens are understood as burial markers for leaders and those of significance in the society. Additionally, they served as places of ritual and worship, with many still containing funerary artifacts that indicate belief in the afterlife and the possibility of communication with the spiritual world.

Popular Article: Nitrogen

Appearance of Nitrogen
Nitrogen (symbol N, atomic number 7) is the chief constituent of the Earth's atmosphere and a vital element in all known forms of life. At ordinary temperatures and pressures, free nitrogen (unbound to any other element) is a colorless, odorless, and tasteless gas. As an inert gas, it reduces the amount of oxygen available for the oxidation of natural materials, thus restricting spontaneous combustion of flammable materials and the corrosion of metals. It also protects living organisms from the toxic effects of breathing pure (or highly concentrated) oxygen. The Earth's nitrogen continually cycles through the atmosphere, biosphere, and lithosphere, effected by such processes as nitrogen fixation by bacteria, metabolic processing in living things, and decomposition of dead organic matter.

In living organisms, nitrogen atoms are part of the molecular structures of such key substances as amino acids, proteins, and nucleic acids. In industry, nitrogen gas is used as an inert replacement for air in the packaging of foods and the manufacture of steel and electronic components. Liquid nitrogen is a cryogen (low-temperature refrigerant) used for freezing and transport of food and other perishable products. Ammonia, a significant compound of nitrogen, is useful for fertilizers and for the synthesis of nitric acid and other valuable compounds. Nitric acid is an oxidizing agent* used in liquid-fueled rockets, potassium nitrate is used in gunpowder, and trinitrotoluene (TNT) is a significant explosive. In addition, nitrogen is a constituent element in every major class of drugs.

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