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.
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.
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.
This is an informational tour in which students gain a basic understanding of geologic time, the evidence for events in Earth’s history, relative and absolute dating techniques, and the significance of the Geologic Time Scale.
The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly.
Scientists use two kinds of dating techniques to work out the age of rocks and fossils. This considers the positions of the different rocks in sequence (in relation to each other) and the different types of fossil that are found in them.
The second method is called absolute dating and is done by analysing the amount of radioactive decay in the minerals of the rocks.
The best examples are fossils of animals or plants that lived for a very short period of time and were found in a lot of places.
Ammonites, shelled relatives of today’s octopus, make ideal index fossils.
Suppose a dinosaur fossil has been found in the beds of an ancient delta (the mouth of a river leading to the sea).