One way to find the age of a xenolith or subsidence area surrounded by volcanic debris is to correlate its layers with the layers of wall or parent rocks.
Stratigraphy is the study of sedimentary rock layers.
The study of fossils and the exploration of what they tell scientists about past climates and environments on Earth can be an interesting study for students of all ages.
Teaching about Earth's history is a challenge for all teachers.
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In this activity, students begin a sequencing activity with familiar items letters written on cards.
To get to that point, there is also a historical discussion and description of non-radiometric dating methods.
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.
The example used here contrasts sharply with the way conventional scientific dating methods are characterized by some critics (for example, refer to discussion in "Common Creationist Criticisms of Mainstream Dating Methods" in the Age of the Earth FAQ and Isochron Dating FAQ).
A common form of criticism is to cite geologically complicated situations where the application of radiometric dating is very challenging.
Sequencing the rock layers will show students how paleontologists use fossils to give relative dates to rock strata.
Once students begin to grasp "relative" dating, they can extend their knowledge of geologic time by exploring radiometric dating and developing a timeline of Earth's history.
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.
Time factors of millions and billions of years is difficult even for adults to comprehend.
However, "relative" dating or time can be an easy concept for students to learn.