A History of Agriculture in India v1.c13.6

v1.c13.6

The same principle is employed in the ¹⁴carbon method, which is, however, limited to the later periods of prehistory. This method is based on the discovery that alongside normal carbon, with an atomic weight of 12, all living organic matter contains various isotopes of this carbon, one of which is radioactive and is, therefore, known as radio-carbon, or, because its atomic weight is 14, as ¹⁴carbon. After death, ¹⁴carbon disintegrates progressively at a rate that has been measured and is believed to be constant. The older a bone or an archaeological object is, the less the radio-carbon it contains, and it is accepted that by the end of 25,000 years the radio-carbon will have totally disappeared. In the case of any object below this age, the quantity of ¹⁴carbon present gives a rough idea of its antiquity. In fact, when applied to articles taken from the Egyptian tombs, whose age is well established, this method has given exact figures. It may be assumed that it is equally accurate for older material.¹