But, how can we determine how old a rock formation is, if it hasn’t previously been dated?Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.
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.
For example, if the cultural contents of the lower deposit are Mauryan in character, appropriately this deposit may be assigned a date between 400-200 B. Similarly, if the cultural equipment of the upper deposit are of the Sunga period, this deposit has to placed between 200-73 B. Quite often, the archaeologist decided the change of stratum on the basis of the feed of the deposit.
In such cases subjective element cannot be ruled out.
A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.
In an undisturbed sequence of rocks, such as in a cliff face, it is easy to get a rough idea of the ages of the individual strata – the oldest lies at the bottom and the youngest lies at the top.
This is because new sediments are always laid down on top of sediments that have already been deposited.
So, when looking at the history of a cliff face, it is important to read the story it tells from the bottom layer up.
The majority of the time fossils are dated using relative dating techniques.
Using relative dating the fossil is compared to something for which an age is already known.
But, even when the scientific methods of absolute dating are available, this method of dating has not lost its importance, as many a time we have to depend solely on relative dating.