Why are index fossils useful for dating rocks xbmc updating to eden
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.
Throughout the history of life, different organisms have appeared, flourished and become extinct.
Many of these organisms have left their remains as fossils in sedimentary rocks.
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 method of reading the order is called stratigraphy (layers of rock are called strata).
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.
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.
Different species of ammonites lived at different times within the Mesozoic, so identifying a fossil species can help narrow down when a rock was formed.