1. Day 1 Vocabulary Review Background terms:
Principle of Uniformitarianism
Doctrine of Catastrophism

2. Day 1 Vocabulary Review Relative Dating principles:
Original horizontality
Superposition
Cross-Cutting Relationships
Intrusion: body of igneous rock forced between or through existing formations, without reaching the surface
example: sill—an intrusion between parallel layers of rock
Faults: a fracture in Earth’s crust that makes rock layers appear discontinuous

3. Day 1 Vocabulary Review Inclusions Unconformities:
Disconformity: sed. layer above sed. layer
Nonconformity: sed. layer above non-sed. layer
Angular unconformity

4. Practice: Sequence the layers!

5. E, G, L, C, H, M, D, J, A, N, K, B, F

6. Calculating the exact numerical age of samples
Absolute Dating
Calculating the exact numerical age of samples

7. Use of Radioactive Isotopes
Radioactive atoms, like the isotope uranium-238, emit particles from their nuclei that we detect as radiation.
Ultimately, the radioactive decay process produces atoms that are stable and no longer radioactive.
Example: uranium-238  lead-206
The amount of time this process takes depends on the isotope.

8. Use of Radioactive Isotopes
Radiometric dating: determining the age of a sample by measuring the percentage of radioactive isotopes remaining within it

9. Half-life: the length of time it takes for one-half of the original parent isotope to change to the daughter isotope.

11. Other Ways to Determine Age
Tree Rings
The age of a tree can be determined by counting the number of annual tree rings in a cross section of the tree.
The width of tree rings are directly related to the climatic conditions during growth periods (spring and winter rings equal one year)
Dendrochronology is the science of comparing annual growth rings to date events and changes in past environments

12. Other Ways to Determine Age
Seasonal Climatic Changes
Varves are bands of alternating light and dark colored sediments of sand, clay, and silt. In the summer months, deposits are light colored and thick… in the winter they are darker and thinner
Varves are similar to tree rings as they show evidence of cyclic events
Varves from different lakes can be compared to determine the ages of glacial lake sediments

13. Other Ways to Determine Age
Distinctive Sediment Layers
When layers are formed by instantaneous or short-lived events, geologists may be able to determine the time of the event through radiometric dating.
This layer is called a key bed, and can correlate rock layers across large areas

15. Types of Fossils Original Preservation Altered Hard Parts
Index Fossils
Molds and Casts
Trace Fossils

16. Original Preservation
Fossils with original preservation have not undergone any significant change since the organism’s death
Contain soft and hard parts
Uncommon because their preservation requires extraordinary environmental conditions (e.g., permanent freezing, desiccation, or anaerobic conditions)
Habitats that favor original preservation
Tundra
Deserts
Bogs
Tar pits
Amber

17. Original Preservation

18. Altered Hard Parts
When all the organic material has been removed and the hard parts of the organism have been changed either by mineral replacement or by recrystallization, fossils are referred to as altered hard parts.
Permineralization: process by which pore spaces are filled in with mineral substances

19. Altered hard parts
Petrified wood (silica fills in spaces between cells walls)

20. Altered hard parts
Silicified marine fossils

21. Index Fossils
Any fossil that can be used to correlate rock layers over large geographic areas or to date a particular rock layer
Particularly useful for relative dating
Characteristics of index fossils
Easily recognized
Abundant
Widely distributed geographically
Must have lived during a short period of time
Provide clues to the environments in which the rocks formed

22. Index Fossils

23. Molds and Casts
Mold: hollow impression left when the original shell parts of an organism within a sedimentary rock are weathered and eroded away
Cast: occurs when minerals or sediment fill in the mold

25. Trace fossils Indirect evidence of previous organisms
Examples: worm trails, burrows, footprints
Provide information about how an organism lived, how it moved, and how it obtained food

26. Correlation
Correlation is the matching of rock layers of one geographic region to another.
Can be useful for the discovery of
oil or other valuable minerals
unique rock or mineral features
distinctive fossils

27. Correlation is often done by comparison of fossils

28. Volcanic Time Markers and Correlation
Violent volcanic eruption can deposit a thin layer of volcanic ash over the entire Earth.
This layer is very distinguishable and is similar to index fossils (cover entire
earth and represent a very short period of time)

29. Why Study Fossils? (Paleontology)
Provides evidence of the past existence of a wide variety of life-forms
~99.9% of all species in earth’s history have gone extinct and can be known only from fossils.
Shows evidence of ancient environmental conditions
Provides evidence that a population has undergone changes (evolution) in response to its environment
Allows scientists to interpret and describe Earth’s history
Helps scientists find patterns and cycles that can be used to predict future phenomena