How old something is in comparison
to something else
Found in sedimentary rock layers
about 400 million years ago
How species have changed over time
Correlation between rock layers from around
Relative ages to particular strata
Evidence for the geological time scale
Law of Superposition
Law that states the older layers were laid down first, then
younger materials was put down on top of it
Younger Igneous Rock
can cut through rock layers
Closer Look at Rock Layers
Do you see evidence of
Principles of Crosscutting
The geologic feature which
cuts another is the younger
of the two features
What kind of rocks are these fossils in?
Which layer is oldest?
Which layer is youngest?
How do you know?
Intrusions vs Extrusions
Intrusion: when magma
cools within the earth
Always younger than the rock around it
Extrusion: when lava
cools outside the earth
Image A Image B