Answer to Question #91135 in Chemistry for Sachin Bhardwaj

Question

Principle of radioactive dating
Carbon & uranium dating

Answer 1

Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest^[1] and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routine precisions in the 0.1–1 percent range

The dating method is usually performed on the mineral zircon. The mineral incorporates uranium and thorium atoms into its crystal structure, but strongly rejects lead when forming. Because of this fact, newly-formed zircon deposits will have no lead content, allowing us to deduce that the entire lead content of the zircon is radiogenic (meaning that it was produced solely by the process of radioactive decay after the formation of the mineral). Since we also know the exact rate at which uranium decays into lead, the current ratio of lead to uranium in a sample of the mineral can therefore be used to reliably determine its age.

The method relies on two separate decay chains, the uranium series from ²³⁸U to ²⁰⁶Pb, with a half-life of 4.47 billion years and the actinium series from ²³⁵U to ²⁰⁷Pb, with a half-life of 710 million years.

More information: https://en.m.wikipedia.org/wiki/Uranium%E2%80%93lead_dating

Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.

The method was developed in the late 1940s by Willard Libby, who received the Nobel Prize in Chemistry for his work in 1960. It is based on the fact that radiocarbon (14

C) is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14

Ccombines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire 14C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14C it contains begins to decrease as the 14

Cundergoes radioactive decay. Measuring the amount of 14C in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died. The older a sample is, the less 14

Cthere is to be detected, and because the half-life of 14

C (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.

More information: https://en.m.wikipedia.org/wiki/Radiocarbon_dating