1. Aim: How do Scientists Read Rocks?
Do Now:
In your notes, answer the following question. Of the three types of rocks we have discussed (Igneous, Sedimentary and Metamorphic), which one do you think would be able to hold clues to Earth’s past? Why?

2. Outcrop – section of rock exposed at the surface that shows a geologic sequence.

3. I. Reading Earth’s History
Uniformitarianism - processes we observe today are most likely the same processes that occurred millions of years ago.
When in Earth’s history does this painting show?
Triassic ~200 mya
Today (2014)
Devonian ~360 mya

4. *Does not tell us the actual age or use numbers to express time.
Relative dating - tells us the sequence in which events occurred.
*Does not tell us the actual age or use numbers to express time.

5. II. Rules for Relative Dating:
Law of Superposition
- sedimentary layers are created flat and even first.
the oldest layers are at the bottom.

6. How did the sequence change in picture below? What caused this?
B. Law of Original Horizontality
- folds disturb these layers after they are lithified .
How did the sequence change in picture below? What caused this?

7. How did the sequence change in picture below?
C. Law of Cross-Cutting Relationships
- layers can be cut afterwards by intrusions and faults.
- Intrusions are layers of magma that melt through pre-existing rock.
How did the sequence change in picture below?

8. The rock being metamorphosized
- Contact Metamorphism – occurs as intrusion touches and metamorphosis's the surrounding rock.
Can you cause the metamorphism of layer that does not exist yet?
Which comes first, the rock being metamorphosized or the magma? NO
The rock being metamorphosized

9. III. Important Features
Volcanic Eruptions –
occur at one specific time and leaves a layers of ash which marks the time eruption.
Do not copy
K-T ash Boundary which marks the end of the Cretaceous Period and the beginning of the Paleogene Period. This layer is 65 million years old and below this layer, scientists find fossils of dinosaurs. Above this layer, there are no dinosaur fossils.

10. Unconformity (UNC)- - a gap in the sedimentary rock record.
- caused by erosion
VIDEO 1

11. Closure 1: Place the letters in relative order from oldest to youngest.