Dating and correlating rock layers

These fossils are very useful for us because we can use them to date the layers of rock that they are found in.

Fossils that can be used in this way are called index fossils, and rock layers with the same index fossils in them can be correlated.

The most useful indication of time equivalence is similar fossil content, provided of course that such remains are present.

The basis for assuming that like fossils indicate contemporary formation is faunal succession.

PALEONTOLOGY, AND in particular the study of dinosaurs, is an exciting topic to people of all ages.

Although most attention in today's world focuses on dinosaurs and why they became extinct, the world of paleontology includes many other interesting organisms which tell us about Earth's past history.

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However, "relative" dating or time can be an easy concept for students to learn.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.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.