track and field athletics, sports of foot racing, hurdling, jumping, vaulting, and throwing varied weights and objects. They are usually separated into two categories: track, the running and hurdling events; and field, the throwing, jumping, and vaulting events. "Meets" are traditionally conducted on an oval track that surrounds an infield for the field events; indoor meets may comprise all but a few of the field events.

Events

Track events include the 100-, 200-, 400-, 800-, 1,500-, 5,000-, and 10,000-meter runs; the marathon race (26 mi 385 yd/42.19 km); the 100- (women), 110- (men) and 400-meter hurdles; the 400- and 1,600-meter relays; the 3,000-meter steeplechase (men); and the 20,000- and 50,000-meter (men) walks. Such British-system equivalents as the 100-yd dash and the mile run may also be part of a meet. Field events include the shot put; the hammer throw; the discus throw; the javelin toss (less frequently); the high jump; the long jump; the triple jump (formerly the running hop, skip, and jump); and the pole vault. The ten-event decathlon is the major composite event for men, and the Olympic winner is traditionally acclaimed as the "world's greatest athlete." The seven-event heptathlon (formerly the five-event pentathlon) is the women's major composite event.

History

Track and field athletics dominated the ancient Greek athletic festivals, and were also popular in Rome, but declined in the Middle Ages. In England they were revived sporadically between the 12th and 19th cent.; the first college meet occurred in 1864 between Oxford and Cambridge universities.

Track and field athletics in the United States dates from the 1860s. The Intercollegiate Association of Amateur Athletes of America, the nation's first national athletic group, held the first collegiate races in 1873, and in 1888 the Amateur Athletic Union (which governed the sport for nearly a century) held its first championships. The Athletics Congress now regulates the sport in the United States; the International Amateur Athletics Federation (IAAF) sanctions international competition. Track and field has been the centerpiece of the summer Olympic games since their revival in 1896. International professional running, initiated in the 1970s, has had limited success.

Record-setting Achievements and Illegal Drugs

Continuous, and often astonishing, improvement has characterized the sport in the 20th cent. Performances once considered unattainable, such as the 4-minute mile (first achieved in 1954 by Roger Bannister, the 8-ft (2.44-m) high jump (achieved by Javier Sotomayor in 1993), and the 20-ft (6.1-m) pole vault (achieved in 1994 by Sergey Bubka) are especially well known. Since the 1970s, many have questioned whether some record-setting achievements have been produced with the aid of performance-enhancing drugs or other unsanctioned techniques. Testing of athletes has therefore become standard, and results have occasionally been nullified, as when Canada's Ben Johnson lost his world record and 1988 Olympic gold medal for the 100-m race after tests detected anabolic steroids in his system.

or track and field also track-and-field games

Variety of sport competitions held on a running track and on the adjacent field. It is the oldest form of organized sports, having been a part of the ancient Olympic Games from circa 776 BC to AD 393. Modern events include various sprint and middle- and long-distance races, relay races, hurdling, steeplechase, high jump, pole vault, long jump, triple jump, shot put, discus throw, hammer throw, javelin throw, decathlon, pentathlon, and heptathlon. Cross-country running, marathons, and speed walking, which are rarely held on a track, are usually considered adjuncts of athletics. Events are held indoors and outdoors, and records are kept separately; some events are modified or eliminated for indoor competition.

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Method of determining the age of a mineral that utilizes the damage done by the spontaneous fission of uranium-238, the most abundant isotope of uranium. The fission results in radiation damage, or fission tracks, that can be made visible by preferential leaching (removal of material by solution) of the host substance with a suitable chemical reagent; the leaching process allows the etched fission-track pits to be viewed and counted under a microscope. The amount of uranium present can be determined by irradiation that produces thermal fission of uranium-235, which produces another population of tracks, related to the uranium concentration of the mineral. Thus, the ratio of naturally produced, spontaneous fission tracks to induced fission tracks is a measure of the age of the sample. See also dating.

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