Dating dinosaurs and other fossils
Fossils themselves, and the sedimentary rocks they are found in, are very difficult to date directly.
Instead, other methods are used to work out a fossil’s age. These include radiometric dating of volcanic layers above or below the fossils or by comparisons to similar rocks and fossils of known ages.
Why date a fossil?
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.
How to date a fossil
There are two main methods to date a fossil. These are:
- absolute dating methods that tell us the actual age (in years) of an object. There are many absolute dating methods. Nearly all of these methods make use of radioactive elements that occur naturally in various types of minerals and organic matter.
- relative dating methods that can only tell us whether one object is older or younger than another – they cannot pinpoint an actual age in years. Relative dating methods are used to work out the chronological sequence of fossils. They can be applied to fossils found at a particular site and can also be used to make comparisons between sites.
Where possible, several different methods are used and each method is repeated to confirm the results obtained and improve accuracy. 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. This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
Dating methods Useful age ranges (years) Materials dated
Absolute dating methods:
Fission track 5000 to 100 million volcanic minerals, teeth
Potassium-argon and
argon-argon 200,000 to > 4 billion volcanic rocks and minerals
Relative dating methods:
Chemical analysis 0 to > 4 billion bone and fossilised bone
Stratigraphy 0 to > 4 billion fossils and other objects found in identifiable layers of sediment or sedimentary rock
Biostratigraphy 0 up to 2 billion similar fossils from different sites
Palaeomagnetic stratigraphy 0 up to 80 million fossils found in layers of identified magnetic orientation
- See more at:
Dating dinosaurs and other fossils - Australian Museum
