Geology 12
Presents

Hand out note helper WS 8.45
Unit Outline
• A: Fossil Record & Geologic Time
– WSs: 8.1, 8.2, 8.3, & 8.4
– Labs: 8.1, 8.2 & 8.3 (bonus)
• B: Relative Dating
– WS: 8.5, Lab 8.4
• C: Absolute Dating
– WS 8.5, Lab 8.5
– Unit 2 Review WS + Unit 2 Test
B: Relative Dating
• Order of events: write numbers on sheet.
8
7
6
5 = erosion
4 = tilting
9
3
2
1
Relative Dating
Relative Dating
• Involves placing events in the correct
sequence or order
15 = erosion
14
13
12 = erosion
10
9
5
4
8 = erosion
7 = tilt = mtn’ bldg’
3
6
2
1
• Absolute Dating is determining how long
ago something happened (ma)
– ie. Dinosaurs became extinct 65 ma ago.
• Using the principle of Uniformitarianism,
six principles have been developed
1. Principle of Superposition: oldest rocks
on bottom; youngest rocks on top.
2. Principle of Original Horizontality:
sediments deposited in water in horizontal
manner.
3. Principle of Lateral Continuity: sediments
continue in all directions until they thin and
are pinched out at the edge of the basin.
4. Principle of Cross-cutting Relationships:
an igneous intrusion (or fault) is younger
than the rock it intrudes (crosses).
3
2
1
4
6
5
7
4
3
9
8
2
1
17-erosion
6
5
7
11 12
10
9
3
2
1
16
14
4
15
13
5. Principle of Inclusions: xenoliths/
inclusions are older than the rocks they’re in.
2
1
3
2
1
3
5 - erosion
4
1
1
5 - erosion
3
2
2
3
4
7
6
5
4
3
2
1
6. Principle of Fossil Succession: fossils on
bottom are older than fossils on top.
Unconformities
• Break or portion of time (hiatus) is missing
• Cause: period of non-deposition, period of
erosion or mountain building
• 3 types
1. Disconformity: surface of erosion or nondeposition (hard to detect)
weathering, oxidation, jointing, etc.
Sed’ Rx
Sed’ Rx
2. Angular Unconformity: beds tilted then
eroded before deposition
(most common on exam)
Angular Unconformity
3. Nonconformity: erosion surface is cut
into metamorphic or igneous rocks. Use
principle of inclusions to determine if it is an
intrusion or a nonconformity.
Sed’ Rx
Ign’ or met’ Rx
Practice Relative Dating Examples
Do Lab 8-4 Relative Dating
 Work on WS 8-5
 Work on Chp. 8 Review WS
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