1. Geologic Time Notes
By studying the characteristics of rocks and the fossils within them geologists can…
interpret the environments in which the rocks were deposited
reconstruct Earth’s history
possibly predict events or conditions in the future.

2. Geologic Time Scale
is a record of Earth’s history from its origin 4.6 billion years ago to the present
This scale shows the similar ages the correlation of geologic events, environmental changes, and the development of life-forms that are preserved in the rock record.

3. Geologic Time Scale is Divided into:
Eon: Largest Division (billions of years before present).
ex: Archean, Phanerozoic
Era: defined by the differences in life-forms found in rock and measured in hundreds of millions to billions of years, is the second-longest span of time on the geologic time scale.
ex: Cenozoic, Paleozoic

4. Period: measured in tens of millions of years before present
Period: measured in tens of millions of years before present. Defined by the life-forms abundance and extinction rate. Third largest span of time.
ex: Triassic, Jurassic

5. Epochs
Epochs: even smaller divisions of geologic time measured in millions of years to tens of millions of years

6. Uniformitarianism: states that processes that have been occurring today such as weathering and mountain building have been occurring since the Earth formed.

7. Stop here

8. How to Determine the Ages of the Rocks
1. Relative Dating: estimating the dates of rocks and fossils according to the other rocks and fossils around it.
2. Absolute Dating: Determining the age of rocks and fossils by doing tests to get the exact age.

9. Principle of Original Horizontality
Sedimentary rocks are deposited in horizontal layers

10. Principle of Superposition: In a rock sequence, the oldest rocks are located at the bottom and the youngest are at the top.

11. Methods for Relative Dating:
Cross-cutting relationships
2. Inclusions
3. Unconformity
4. Correlation

12. Cross-cutting relationships: states that an intrusion or a fault is younger than the rock it cuts across.

13. Unconformity: Gap in the rock record usually caused by an eroded surface becoming buried by the deposition of younger rocks.

14. Correlation: the matching of outcrops of one geographic region to another.
Ex: If a sandstone layer in one area contains oil, it is possible the same layer in a different area also contains oil.

15. Absolute Dating Methods:
Radioactive Decay constant break down of an element over time. Is not affected by any sort of physical changes.
Radiometric Dating scientist use the decay rate of elements to determine how old things are
Half-life time it takes for ½ of the original element to decay into another element
Tree Rings
Seasonal Climatic Changes
Distinctive Sediment Layers.

16. Fossils: Evidence of once living material
1. Original Preservation:

17. 2. Altered Hard Parts: When the Hard parts of an organism have been removed and replaced with minerals.

18. 3.Molds and Casts: molds are the impression that organisms leave in rocks and Casts are when they are filled in with minerals.

19. 4.Index Fossil: the remains of a plant or animal that can be used to correlate rock layers or to date particular rock layers.
5.Trace Fossils: Indirect evidence of plant and animal life.
Ex: tracks