Radiometric dating age of fossils
Potassium-40 on the other hand has a half like of 1.25 billion years and is common in rocks and minerals.
This makes it ideal for dating much older rocks and fossils.
Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
Index fossils are fossils that are known to only occur within a very specific age range.
A common form of criticism is to cite geologically complicated situations where the application of radiometric dating is very challenging.
These isotopes break down at a constant rate over time through radioactive decay.
By measuring the ratio of the amount of the original (parent) isotope to the amount of the (daughter) isotopes that it breaks down into an age can be determined.
Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.
If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between 410 and 420 million years.