1. “The Present is the Key to the Past”
James Hutton, 1700’s

2. History of Geology
The concept and measurement of geologic time has changed through human history.
Planet Earth,The Living Machine p1.mp4 7:15 – 8:00
James Ussher ( ) in Ireland
calculated the age of Earth based on recorded history and genealogies in Genesis
he said that Earth was created on October 22, 4004 B.C.
it was considered heresy to say Earth was more than about 6000 years old.

3. Catastrophism Catastrophism proposed by Georges Cuvier (1769-1832)
Huge catastrophies caused major changes to Earth’s geology and biology in a short period of time.
six major catastrophes occurred, corresponding to the six days of biblical creation, the last one was the biblical flood.

4. Uniformitarianism
Developed by James Hutton, advocated by Charles Lyell ( )
“The Present is the Key to the Past”, James Hutton, 1700’s
What happens today is what happened in the past.
Earth changes very slowly.
Supports a very old age of Earth.
Earth is believed to be about 4.6 billion years old

5. NeoCatastrophism Blends Uniformitarianism with some Catastrophism.
Earth developed and changed at a very slow rate like today, but had some catastrophic event s that caused some sudden changes.
Eg: extinction of dinosaurs
Asteroid collision, Gamma-ray Bursts . . .

6. Relative Dating This is not about dating your sister!! 
Tells us the sequence in which events occurred in a rock.
Which formed 1st, 2nd, etc. . .
NOT how long ago they occurred.

7. Laws and Principles Law of Superposition Youngest Oldest
In an undisturbed sedimentary rock, each bed is older than the one above it and younger than the one below it.
Youngest
Oldest

8. Laws and Principles Principle of Original Horizontality
Layers of sediment are generally deposited in a horizontal position.
Rocks that are folded or tilted must have been moved into that position AFTER their formation.
What happened first?
What happened second?
Horizontal deposition
Folding

9. Laws and Principles Principle of Cross-Cutting Relationships
When a fault or igneous intrusion cuts through another rock,
the fault or intrusion is YOUNGER than rock it cut through.
Igneous Intrusion

10. Laws and Principles Principle of Inclusions
Inclusions are pieces of one rock found in another.
The rock containing the inclusions is YOUNGER than the rock the inclusions came from.
Older
Younger
Inclusions

11. Laws and Principles Principle of Unconformities
Represents a long period during which deposition is stopped, erosion removed rock and then deposition started again.
Angular unconformity
The first layers were tilted before the deposition started again.
Disconformity
When two layers of sedimentary rock are separated by an erosional surface but are still parallel to eachother.
Nonconformity
Erosional surface separates older igneous rocks from younger
sedimentary rocks.

12. Principle of Unconformity
Which type of Unconformity is which???
Disconformity Angular Unconformity Nonconformity

13. Relative Dating
Place the following layers in order of occurrence from OLDEST to YOUNGEST. Include the Fault and unconformity. 8. 7. 6. 5. 4. 3. 2. H R M
Unc
Fault F B I
Youngest
Oldest

14. Fossils: Evidence of Past Life
What is a Fossil?
Preserved remains or traces of prehistoric life.
The type of fossil formed is determined by the conditions the organism died and was buried.

15. Fossils: Evidence of Past Life
The two conditions necessary for the formation of fossils is:
Having HARD parts
Rapid BURIAL

16. Fossils: Evidence of Past Life
Forms of Fossilzation
Mold and Cast
Mold: the hollow shape of the organism left after water dissolved the hard part (shell)
Cast: the solid COPY of the shape of the organism
Mold
Cast

17. Fossils: Evidence of Past Life
Other forms:
Petrified: Minerals replace all or part of the organism. Shows interior detail
(Quartz) Ex: Petrified Wood
Carbon Films: A thin coating of carbon on the rock. The carbon is left from the organism itself. (plants and insects)
Impressions: a copy of the surface of organism
Trace Fossils: clues that an organism was there. (Foot prints)

18. Fossils: Evidence of Past Life
Fossil Succession
Fossils succeed one another in a definite order. (Simpler organisms = older rocks)
Any time-period can be recognized by its fossil content.
Jurassic Period

19. Laws and Principles Fossil Correlation Index fossils: Fossils that are
Matching similar rock types found in different areas.
Index fossils: Fossils that are
Widely distributed
Lived a short time

20. Rock Correlation with Fossils
Activity Answer Key
Unconformity 

21. Radiometric Dating Radioactive Elements
Unstable elements break down or DECAY.
Occurs when the Nucleus changes (Protons and Neutrons change).
During Radioactive Decay, one element breaks down into another element giving off ENERGY.

22. Radiometric Dating Occurs in IGNEOUS rocks.
The RATE OF DECAY is CONSTANT!
Scientists use that rate to determine AGE of a rock.

23. Radiometric Dating Half-Life
The time it takes for half of the radioactive atoms to decay into another element.
Parent material = Radioactive Element
Daughter product = the stable element the radioactive element decays into.
Example: Carbon 14 turns into Nitrogen 14
Carbon 14 = Parent material
Nitrogen 14 = Daughter product
Carbon-14’s half-life is 5,730 years. (what does that mean?)
It takes 5,730 years for half of C14 atoms to decay into N14.

24. Radiometric Dating
Potassium 40 – Argon 40 Dating (K  Ar) (Beta capture)
Parent = Potassium Daughter = Argon 40
Half-life = 1.3 billion years.
Can be used to date rocks because of its long half-life.
Why do you need a LONG half-life to date rocks?
Because rocks are old so if half-life is short, there will be NO Parent element in the rock, only the Daughter product. You need Both to determine age.

25. Carbon-14 Nitrogen-14 Cycle
All living things have C-14 in them.
This begins to turn to N-14 the moment they die.
Can only be used for dating if there is some C14 remaining in the organism

26. Radiometric Dating
Carbon 14 – Nitrogen 14 (C14 – N14): (Beta emission)
Called Carbon Dating.
Only used for dating things ONCE LIVING.
Decay begins when the organism dies.
Only works for things YOUNGER than 75,000 yrs.
Iceman found in in the European Alps. He died 53,000 years ago.

27. Radiometric Dating How to determine age of rock using Half-lives
Half-life
Parent element
Daughter product 1
1/2 2 3
1/8
7/8 4
1/16
15/16
Each Half-life: Parent goes down by ½ Daughter increases by that amount

28. Radiometric Dating NO This can be done by Percentage too.
Half-Life
Parent element
Daughter product
100% 1
50% 2
25%
75% 3
12.5%
87.5% 4
6.25%
93.75%
Mathmatically, does the Daughter product EVER reach 100%? NO

29. Radiometric Dating 17190 years ago! Now lets add HALF-LIFE YEARS.
Parent element (C14)
Daughter product (N14)
0 yrs
100% 0%
5730 yrs
50%
11,460 yrs
25%
75%
17190 yrs
12.5%
87.5%
22920 yrs
6.25%
93.75%
So if we measured a sample of a mummy and found it to be 12.5% C14 and 87.5% N14, how long ago did he die?
17190 years ago!

30. Radiometric Dating Importance of Radiometric Dating
Provided dates for events in Earth’s History.
Supported beliefs of James Hutton, Charles Darwin and others who said Earth is VERY OLD.
There has been enough time for major changes to have occurred geologically.

31. Geologic Time Scale Earth = 4.6 Billion years old (byo)
Earth’s time span is SOOOO GREAT, that scientists have divided it into smaller units of time making the “Geologic Time Scale”.
This division of time helps people grasp this expanse of time.
Scientists used changes in major life-forms and extinctions to divide the time scale.
The division of the time scale is broken into 4 sections.

32. Geologic Time Scale
The 4 major divisions are???
Eon
Era
Period
Epoch

33. Geologic Time Scale 88% of Earth’s History Other 12% PreCambrian
Very little evidence of life.
Other 12%
Phanerozoic
Sudden development of life in the oceans.
Hard parts developed which increased the fossil record.
Visible Life
Single-cell

34. Geologic Time Scale Eras (Divided by major extinctions)
Paleozoic (Hard parts developed)
Marine animals thrived
Pangaea formed
Extinction
90% of marine animals became extinct.
Mesozoic
Dinosaurs developed
Pangaea began to break up.
Dinosaurs
Cenozoic
Mammals became dominant
Humans evolved
Mammals
Dinosaur extinction
Reptiles (Dino)
Marine extinction
Water animals
Single-cell

35. Geologic Time Scale Dinosaurs Humans
Lived on Earth for million years.
Humans
Lived on Earth for thousand years.
Mammals
Dinosaur extinction
Reptiles (Dino)
Marine extinction
Water animals
Single-cell

36. Historical Geology
THE END