Seriation, also called artifact sequencing, is an early scientific method of relative dating, invented (most likely) by the Egyptologist Sir William Flinders Petrie in the late 19th century.
Petrie's problem was that he had discovered several predynastic cemeteries along the Nile River in Egypt that seemed to be from the same period, but he needed a way to put them in chronological order.
The second method is called absolute dating and is done by analysing the amount of radioactive decay in the minerals of the rocks.
Scientists find out the age of a dinosaur fossil by dating not only the rocks in which it lies, but those below and above it.
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.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.
Accurate dates also allow us to create sequences of evolutionary change and work out when species appeared or became extinct. These are: Where possible, several different methods are used and each method is repeated to confirm the results obtained and improve accuracy.
On the other hand, absolute dating includes all methods that provide figures about the real estimated age of archaeological objects or occupations.
These methods usually analyze physicochemical transformation phenomena whose rate are known or can be estimated relatively well.
Different methods have their own limitations, especially with regard to the age range they can measure and the substances they can date.
A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.