1. Age of earth
pg 46-47

2. Relative Dating
Telling the age of the earth using the layers of rocks that are stacked on top one another (figure the layers, figure the age)
Strata: Layers of rock
Relative age indicates that one layer is older or younger than another layer, but does not indicate the rock’s age in years (absolute age).

3. Think about it How are sedimentary rocks formed?
Sedimentary rocks form when new sediments are deposited on top of old layers of sediment.
As the sediments accumulate, they are compressed and harden into sedimentary rock layers.

4. Law of Superposition
An undeformed sedimentary rock layer is older than the layers above it and younger than the layers below it.
The closer you are to the surface the younger you are

5. Turn to Page 11R

7. Principle of Horizontally
Sedimentary rock forms in horizontal layers
If the rock is left alone it forms horizontally. (Then we can figure out the age in layers)
If the rock is not horizontal then it must have been disturbed or deformed after layers were formed (plate movement)

8. Unconformity Break in the geologic record
Sometimes the earth moves and exposes new rocks to the surface making the layers uneven.
Shows that deposition stopped for a period of time, and rock may have been removed by erosion before deposition resumed.

9. There are three types of unconformities.
Disconformity: when young and old horizontal layers of sedimentary rock overlay on eroded deposited surfaces
Nonconformity: stratified layers of rock rest on a unstratified rock
Angular unconformity: The boundary between a set of tilted layers and a set of horizontal layers

10. Law of Crosscutting relationships
A fault or intrusion is always younger than all the rocks it cuts through above and below the unconformity.
(When rock layers have been disturbed by faults (a break or crack in Earth’s crust) or intrusions (a mass of igneous rock that forms when magma is injected into rock and then cools and solidifies, determining age is difficult.)

11. Relative Age
Based on what you now know about the Law of Superposition, the Principle of Original Horizontality, unconformities, and the Law of Crosscutting Relationships can you place the layers indicated in the diagram in the correct order, starting from the oldest layer?

12. The oldest layer is Q, followed by O, then N, then M, then L
The oldest layer is Q, followed by O, then N, then M, then L. P cuts across layers L-Q, so it is the next layer since it does not cut into layer H. Above the unconformity we then have layer H, followed by I, then J, with K being the youngest layer.

13. Drill Core Notes

14. What are we looking for?
Fossils in the earth that have been imprinted into sedimentary rock.
Think superposition
Layers closer to the bottom are older, but how do we know if sometimes we have dikes?
Layers closer to the bottom are older, but how do we know if sometimes we have dikes?
Did some organisms exist at different times?

15. What is a Drill core
Scientists drill into the earth collecting samples about as big as your hand.
A vertical circle cut of rock, deep from the earth.

16. Why do we drill for cores
The samples contain fossils and ancient biomolecules only found in those time periods.
Ancient biomolecules are used for fossil dating, climate and atmospheric readings

17. But what about superposition and dikes?
Long drill cores are collected
The samples are tested for Biomolecules
Some molecules are only found in certain periods

20. Stop

21. *Index Fossils
Paleontologists can use fossils to determine the relative ages of the rock layers in which the fossils are located. Fossils that occur only in rock layers of a particular geologic age are called index fossils.
To be an index fossil, a fossil must meet certain requirements:
1. It must be present in rocks scattered over a large region.
2. It must have features that clearly distinguish it from other fossils.
3. Organisms from which the fossil formed must have lived during a short span of geologic time.
4. The fossil must occur in fairly large numbers within the rock layers.
Image from the website:

22. Word Bank Pg 50 -Deposition -Law of superposition -Lava -Magma
-Unconformity
-Index fossils
-Law of superposition
-Principle of horizontally
-Law of Cross relationships
-Lithification