Age
Age, a term for (1) periods of time, as in human history or the history of the earth, and (2) the length of time an organism has lived or normally lives, or the length of time an object or material has existed.
The Stone Age, Bronze Age, and Iron Age are broad stages in the development of civilization, named for the materials from which humans made tools. In the history of a country, an entire era is sometimes known by the name of a prominent person. Examples are the Age of Pericles in ancient Greece and the Elizabethan Age in 16th-century England. Periods in the history of Western civilization are also sometimes called ages—the Age of Faith and the Age of Exploration, for example.
A period in the history of a nation or people when the level of achievement is notably high is sometimes called a golden age. Golden Age.)
Some periods of time in the history of the earth have been given the name age—for example, the Age of Reptiles. Geologists use the term age to mean a subdivision of an epoch. (See Geology, subtitle Geologic Time.)
For methods used by archeologists, geologists, and other scientists to determine the age of an object or material,
Longevity and AgingThe longevity of an organism is its length of life, or life span. Longevity depends mainly on the organism's species. Creosote bushes, bristlecone pines, and giant sequoias live for thousands of years. The longest-lived animals are certain types of clams and tortoises that live more than 150 years. Some whales live about 100 years, and some elephants and fish about 80 years. The females of several species, including humans, tend to live longer than the males.
Aging, or senescence, is the gradual deterioration of body tissues and body functions that occurs as an organism becomes older. Aging sets an upper limit to longevity in warm-blooded animals (birds and mammals). A human's characteristic longevity is between 70 and 80 years, although some individuals live to be more than 100. Many species of cold-blooded animals (reptiles, amphibians, fishes, and invertebrates) and most plants also have a characteristic longevity. However, aging is either imperceptible or absent.
The average longevity of a group is the age most individual organisms in the group actually reach, as shown by mortality (death) rates. It may be sharply fixed, as for plants and animals that normally die soon after reproduction. Or it may vary greatly with conditions, as for organisms that are normally killed by predators or disease at an early age.
Average longevity in humans is often expressed as life expectancy—the number of years a person can expect to live under current conditions. For example, in 1991 the life expectancy of a male baby born in the United States was about 72 years; that of a female baby, about 79 years.
also Geriatrics; Mortality; Population, subtitle Population Growth.