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.
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.
Correlation can involve matching an undated rock with a dated one at another location.
Relative age dating and absolute age dating
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.
Some fossils, called index fossils, are particularly useful in correlating rocks.
The method of reading the order is called stratigraphy (layers of rock are called strata).
Relative dating does not provide actual numerical dates for the rocks.
Next time you find a cliff or road cutting with lots of rock strata, try working out the age order using some simple principles: Fossils are important for working out the relative ages of sedimentary rocks.Throughout the history of life, different organisms have appeared, flourished and become extinct.Unfortunately, the page you were looking for no longer exists.We are currently working on a new website that will update many of our older web pages.See our current news blog: Digging the Fossil Record Also check out our plans for our Deep Time exhibit hall, to open in 2019 And check out the links on the side bar to the left.Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.