A family of people often consists of related but not identical individuals. Elements have families as well, known as isotopes. Isotopes are members of a family of an element that all have the same number of protons but different numbers of neutrons. For example, carbon has six protons and is atomic number 6. Carbon occurs naturally in three isotopes: carbon 12, which has 6 neutrons plus 6 protons equals 12 , carbon 13, which has 7 neutrons, and carbon 14, which has 8 neutrons. Every element has its own number of isotopes.
Growth ring , in a cross section of the stem of a woody plant , the increment of wood added during a single growth period. Growth rings are distinct if conducting cells produced early in the growth period are larger spring, or early, wood than those produced later summer, or late, wood or if growth is terminated by a layer of relatively thick-walled fibres or by parenchyma. In temperate or cold climates the age of a tree may be determined by counting the number of annual rings at the base of the trunk or, if the trunk is hollow, at the base of a large root. Annual rings have been used in dating ancient wooden structures, especially those of the American Indians in the dry southwestern regions of the United States; fluctuation in ring width is a source of information about ancient climates. Growth ring Article Media Additional Info.
Research illuminates inaccuracies in radiocarbon dating
Election , the formal process of selecting a person for public office or of accepting or rejecting a political proposition by voting. It is important to distinguish between the form and the substance of elections. In some cases, electoral forms are present but the substance of an election is missing, as when voters do not have a free and genuine choice between at least two alternatives. Most countries hold elections in at least the formal sense, but in many of them the elections are not competitive e.
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