Fossil dating worksheet
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 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.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.The sediment of this area was laid down after ammonite A appeared 199 million years ago, and before ammonite B became extinct 195 million years ago.A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.
Index fossils are fossils that can be used to date the rock in which they are found.
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.
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.
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).