Relative dating for fossils
Artifacts found in a layer can be compared with other items found in layers of similar age and placed in order.
However, archeologists still require further information to find out the items that are oldest and those that are youngest in the order.
Two broad categories of classification methods are relative dating and absolute dating.
Though using similar methods, these two techniques differ in certain ways that will be discussed in this article.
Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.
This matching process is called correlation, which has been an important process in constructing geological timescales.
For a fossil to be a good index fossil, it needs to have lived during one specific time period, be easy to identify and have been abundant and found in many places. If you find ammonites in a rock in the South Island and also in a rock in the North Island, you can say that both rocks are Mesozoic.
Relative dating does not provide actual numerical dates for the rocks.
Fossils are important for working out the relative ages of sedimentary rocks.
Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.
The method of reading the order is called stratigraphy (layers of rock are called strata).