Principles of relative age dating
This has also helped them to know how old the earth is. This simply means that sediments are usually deposited in horizontal layers. A process called relative-age dating helps scientists determine how old these rock layers are.Some fossils, called index fossils, are particularly useful in correlating rocks.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.Your goal is to study the smooth, parallel layers of rock to learn how the land built up over geologic time.
These techniques were first articulated by Nicolas Steno, a Dane living in the Medici court of Italy in the 17th C.
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).
Suppose you find a fossil at one place that cannot be dated using absolute methods.
That fossil species may have been dated somewhere else, so you can match them and say that your fossil has a similar age.
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Throughout the history of life, different organisms have appeared, flourished and become extinct.