he question of the ages of the Earth and its rock formations and features has fascinated philosophers, theologians, and scientists for centuries, primarily because the answers put our lives in temporal perspective.Until the 18th century, this question was principally in the hands of theologians, who based their calculations on biblical chronology.Other useful radioisotopes for radioactive dating include Uranium -235 (half-life = 704 million years), Uranium -238 (half-life = 4.5 billion years), Thorium-232 (half-life = 14 billion years) and Rubidium-87 (half-life = 49 billion years).The use of various radioisotopes allows the dating of biological and geological samples with a high degree of accuracy.Before the full potential of natural tritium as a tracer for water movement in natural systems could be explored its distribution was masked by addition of large amounts of so-called ‘bomb tritium’ produced during the surface tests of nuclear weapons.These tests which were mainly performed in the early 1960s, led to an increase of tritium in precipitation over the continents of the northern hemisphere from roughly 5 TU to levels of the order of 1000 TU. Tritium is produced naturally in the upper atmosphere by interaction of nitrogen, and, to a lesser extent, oxygen with cosmic rays.After oxidation to HTO, it takes part in the natural water cycle.
The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced.However, radioisotope dating may not work so well in the future.Anything that dies after the 1940s, when Nuclear bombs, nuclear reactors and open-air nuclear tests started changing things, will be harder to date precisely. Carbon dating has given archeologists a more accurate method by which they can determine the age of ancient artifacts. Libby invented carbon dating for which he received the Nobel Prize in chemistry in 1960.The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample.