1. SEVEN PRINCIPLES Of GEOLOGY 1. UNIFORMITARIANISM:
-The processes that shape the Earth today are the same processes that occurred in the geologic past
“The present is the key to the past”

2. 2. ORIGINAL HORIZONTALITY
-Sedimentary rock layers are ALWAYS laid down in horizontal layers, until some other process alters them

3. Original Horizontality
sedimentary rocks form in horizontal layers parallel to Earth’s surface and will remain that way unless disturbed
SILT
SAND
CLAY
SILT
CLAY
EARTH'S SURFACE

4. Horizontal Layers of the Grand Canyon

5. 3. SUPERPOSITION
-The bottom layer of horizontal sedimentary rock layers is always the oldest, UNLESS the layers have been overturned or have had older rock formed on top of it
*The lower layers must first be in place before the next layer can be deposited

6. YOUNGEST
OLDEST

7. LAW OF SUPERPOSITION
For undisturbed rocks, the oldest layer is on the bottom and the youngest is on top
Supai is oldest – WHY?

9. Law of Superposition Top = youngest layer
In undisturbed sedimentary rock or lava flows
In undisturbed sedimentary rock or lava flows:
Top = youngest layer
Bottom = oldest layer

10. Unconformity Gaps or missing layers in the rock record due to erosion
Angular unconformity

11. Unconformities: 3 Types1 2 3

12. Igneous Extrusions & Intrusions
When molten rock flows on the Earth’s surface forming an igneous rock

13. -Causes surrounding layers to metamorphose (Contact metamorphism)
Intrusion:
Occurs when magma squeezes between layers of pre-existing rock beneath the Earth’s surface
-Causes surrounding layers to metamorphose (Contact metamorphism)

14. Igneous Intrusions

15. 4. Cross-Cutting Relationships
Igneous intrusions/extrusions that “cut across” or enter other rocks are younger than the rocks they cross

16. Law of Cross-Cutting Relationships
Any feature that cuts across a rock or layer of sediment is younger than the rock or layer it cuts
youngest layer

17. Example of Cross-Cutting
Intrusion - igneous rock that forms when magma squeezes between existing rock and hardens
Intrusion - igneous rock that forms when magma squeezes between existing rock and hardens

18. Examples of Cross-Cutting
Example of Cross-cutting
(extrusive)
Examples of Cross-Cutting
Extrusion - igneous rock that forms when lava
flows on Earth’s surface and hardens

19. Principle of Cross-Cutting Relationships James Hutton ( An igneous intrusion or a fault event must be younger than the rocks it intrudes or cuts across

20. Cross-cutting Relationships
North shore of Lake Superior, Ontario Canada
A dark-colored dike has intruded into older light colored granite.
The dike is younger than the granite.

21. Cross-cutting Relationships
Templin Highway, Castaic, California
A small fault displaces tilted beds.
The fault is younger than the beds.

22. Sequence of Events
Key to Rock Types

23. 5. Fossil (faunal)Succession
Fossils of different Plants and Animals are found in sedimentary rock layers. When different fossils are found in the same layer, they existed during the same time period.

25. 6. Law of Inclusions
Rock particles/fragments that are found in rock layers are older than the rock layer it is found in.

26. Principle of inclusions That which is included is _________ (older
Principle of inclusions That which is included is _________ (older? Younger?)

27. 7. Lateral Continuity (Lateral means “side to side”)
Igneous intrusions that “cut across” or enter other rocks are younger than the rocks they cross.

28. FOLDS AND FAULTS Folds and Faults are always younger than the original
rock layers
Fold:
-bends in rock layers produced by movements of the earth’s crust
Faults:
-breaks in the rock where shifting of rock layers has occurred, often associated with earthquakes

29. Principles of Geology: Big Ideas
(you should know)
7 Laws of Geology
Relative aging of rock using Superposition
Definitions of intrusion, geologic dike, unconformity
Matching rock layers using fossils
Definitions: folding, fault, uplifting