12. Fossils in Sedimentary Rocks
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Mold: hollow area left by the living thing
Cast: solid mineral deposit that filled the mold, leaving a copy
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21. Trilobite
Fossils show:
Biodiversity
How species have changed over time
Correlation between rock layers from around
the world
Relative ages to particular strata
Evidence for the geological time scale
22. 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
23. Closer Look at Rock Layers
Do you see evidence of
Erosion
Earthquake
A river
25. What kind of rocks are these fossils in?
Which layer is oldest?
Which layer is youngest?
How do you know?
26. 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
Image C
34. Absolute Dating
The actual age of the event
Half Life: the length of time it takes for half of the atoms
in a sample of a radioactive element to change from an
unstable form into another form