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 (2015)
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.
the oldest layers are at the bottom.
How many layers of rock are there? Which is the oldest?

6. How did the sequence change in picture below? What caused this?
B. Law of Original Horizontality
- folds/faults disturb (mess-up) 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 after they form by intrusions and faults.
- Intrusions are layers of magma that melt through pre-existing rock and then solidify.
How did the sequence change in picture below?

8. Igneous Intrusion cuts through the pre-existing rock.
- Which came first, the intrusion or the rock it is in?
- Which principle lets us know this?

9. - Contact Metamorphism – a symbol that shows which rocks have been affected by the intruding magma.
- indicates the rocks have been affected by the intrusion when it was magma.
Analyze these two geologic cross sections, describe how they are different?

10. What else indicates one specific time?
III. Important Features
Ash Layers –
Created by erupting volcano, occurs at one specific time and indicates the time eruption.
What else indicates one specific time?
Do not copy
This layer is 65 million years old. Below this layer, scientists find fossils of dinosaurs. Above this layer, there are no dinosaur fossils. What does this layer tell us?
K-T ash Boundary which marks the end of the Cretaceous Period and the beginning of the Paleogene Period.

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

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