Relative or absolute dating
We define the rate of this radioactive decay in half-lives.
If a radioactive isotope is said to have a half-life of 5,000 years that means after 5,000 years exactly half of it will have decayed from the parent isotope into the daughter isotopes.
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.
There are two main methods determining a fossils age, relative dating and absolute dating.
Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.
It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.Absolute dating and relative dating are two techniques used in geology to evaluate the age and the period of a fossil or rock. What is Absolute Dating – In geology, absolute dating is a technique that determines the exact numerical age of a historical remaining.Since it evaluates the exact age of the sample, absolute ageing is also called numerical dating.The Wheeler Formation has been previously dated to approximately 507 million year old, so we know the trilobite is also about 507 million years old.But, how can we determine how old a rock formation is, if it hasn’t previously been dated?
Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it.