Licensed from Columbia University Press
Licensed from Columbia University Press
See B. Tharaud, ed., Yaşar Kemal on His Life and Art (1999).
Licensed from Columbia University Press
See F. W. Buckler, Harunu'l-Rashid and Charles the Great (1931); H. St. John B. Philby, Harun al Rashid (1933).
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
See R. Knapp, Roman Córdoba (1983).
Licensed from Columbia University Press
See R. Collins, Early Medieval Spain: Unity in Diversity (2 vol., 1983-87); S. Lane-Poole, The Moors in Spain (1984); D. Taha Abdulwahid, Muslim Conquest and Settlement of North Africa and Spain (1988).
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
(born March 763 or February 766, Rayy, Iran—died March 24, 809, Tsubdotūs, Iran) Fifth caliph of the
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Method for determining the age of igneous rocks based on the amount of argon-40 in the rock. Radioactive potassium-40 decays to argon-40 with a half-life of about 1.3 billion years, making this method useful for dating rocks that are billions of years old. A more sophisticated method, called argon-argon dating, provides a more accurate estimate of the original potassium-40 content by means of the ratio of argon-40 to argon-39 in the rock, thus yielding a more accurate age determination. Seealso dating.
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Chemical element, chemical symbol Ar, atomic number 18. Colourless, odourless, and tasteless, it is the most abundant of the noble gases on Earth and the one most used in industry. It constitutes about 1percnt of air and is obtained by distillation of liquid air. Argon provides an inert gas shield in welding and brazing, in lightbulbs and lasers, in Geiger counters, and in the production and fabrication of certain metals. Because a radioactive form of argon is produced by decay of a naturally occurring radioactive potassium isotope, it can be used to date rocks and samples more than 100,000 years old.
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