The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. This process by which an unstable atomic nucleus loses energy by releasing radiation is called radioactive decay.
Since 1955 the estimate for the age of the Earth has been based on the assumption that certain meteorite lead isotope ratios are equivalent to the primordial lead isotope ratios on Earth.
In 1972 this assumption was shown to be highly questionable.
This chain eventually ends with the formation of a stable, nonradioactive daughter nuclide.
Each step in such a chain is characterized by a distinct half-life.
The igneous activity that produced such intrusions...
...calculation was based on the assumption that the substance of the Earth is inert and thus incapable of producing new heat.
Radiometric dating, often called radioactive dating, is a technique used to determine the age of materials such as rocks.
It is based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.
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Scientific knowledge of Earth’s geologic history has advanced significantly since the development of radiometric dating, a method of age determination based on the principle that radioactive atoms in geologic materials decay at constant, known rates to daughter atoms.