Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.
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.
Geologists call this the principle of lateral continuity.
A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.
Current understanding of the history of life is probably close to the truth because it is based on repeated and careful testing and consideration of data.
The rejection of the validity of fossils and of dating by religious fundamentalists creates a problem for them: Fossil sequences were recognized and established in their broad outlines long before Charles Darwin had even thought of evolution.
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.
So, when looking at the history of a cliff face, it is important to read the story it tells from the bottom layer up.
There are two main methods determining a fossils age, relative dating and absolute dating.
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.
Sometimes, scientists already know the age of the fossil because fossils of the same species have been found elsewhere and it has been possible to establish accurately from those when the dinosaur lived.