Earth Science

Section 4.2BRock Layers and Geo Time

Relative age

1. Read both paragraphs on pg. 119B.2. Give an example where you know the relative

age of something, but not the exact age. a) World War II plane compared to modern jet.

3. What’s the difference between relative age and exact age?

a) Relative age tells you that something is younger or older than something else, but not the actual age of it.

Superposition

• Read the paragraphs on pg. 120B and look at the two pictures.

• Do 4 bullet notes from each paragraph• When looking at a stack of exposed

sedimentary rock layers, the oldest layer will be …– On the bottom

continued

• How is it possible that an older layer will be above a younger layer of rock?– Plate movements can disturb rock layers, folding

the older layers over the top of some younger layers.

Igneous intrusions

• Read the two paragraphs in the “Igneous Rock and Sedimentary Layers” section on pg. 121B.

• Sketch diagram 2 (in color) and label the relative ages of the layers compared to the igneous rock that cut through those layers.

Younger Igneous rock that cut through the

oldest layers

Oldest layers

Youngest layers formed above the igneous rock

Index Fossils

• Do a description wheel for “index fossils”

IndexFossil