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It has a half-life of 1.3 billion years, meaning that over a period of 1.3 Ga one-half of the Figure 8.4.1 The decay of 40K over time.Each half-life is 1.3 billion years, so after 3.9 billion years (three half-lives) 12.5% of the original 40K will remain.One good example is granite, which normally has some potassium feldspar (Figure 8.4.2).Feldspar does not have any argon in it when it forms.The carbon dioxide mixes throughout the atmosphere, dissolves in the oceans, and via C in the original sample will have decayed and after another 5568 years, half of that remaining material will have decayed, and so on.This half-life (t 1/2) is the name given to this value which Libby measured at 556830 years. After 10 half-lives, there is a very small amount of radioactive carbon present in a sample.
Shortly after Becquerel's find, Marie Curie, a French chemist, isolated another highly radioactive element, .For the first time he was able to exactly measure the age of a uranium mineral.When Rutherford announced his findings it soon became clear that Earth is millions of years old.It is also based on the premise that when the atoms of an element decay within a mineral or a rock, they stay there and don’t escape to the surrounding rock, water, or air.
One of the isotope pairs widely used in geology is the decay of K is a radioactive isotope of potassium that is present in very small amounts in all minerals that have potassium in them.The realisation that radioactive materials emit rays indicated a constant change of those materials from one element to another.