1. Chapter 8: The Rock Record

2. Chapter 8- Pretest
12 questions

3. Section 1: Determining Relative Age

4. James Hutton 18th century geologist Physician and farmer
Observed geologic changes that occurred on his farm
Same changes that he observed on his farm also changed the Earth’s surface in the past.
Studying the past we can learn about the future.

5. James Hutton observed small changes on his farm over a long period of time
Suggesting the Earth is older than he thought.
Earth is about 4.6 Billion years old.

6. Principle Of Uniformitarianism
Uniformitarianism: a principle that geologic processes that occurred in the past can be explained by current geologic processes
Basic foundation of geology!!
“The present is the key to the past” – Charles Lyell

7. Age of Earth
Even though the processes of the past and present are the same
The rates of these processes over time vary
Before Hutton
Earth was only 6,000 years old
Observations that changed his land happened very slowly
Earth must be older than we originally thought
Studying the order rock layers and other structures formed we can learn about Earth’s past

8. Relative Age
Relative Age: the age of an object or rock layer in relation to the ages of other objects.
Determining age from surrounding objects.
Indicates that one layer is older than another layer
But does not indicate the age in years.
Sedimentary rocks are studied to determine relative ages
Sedimentary rock layers are called strata

9. Exit Ticket 
How old is Earth?

10. 3/14 Warm up
Explain relative age.

11. Yesterday Recap James Hutton Uniformitarianism Relative Age
Age of Earth

12. What is the Rock Record? The “record” of rocks that currently exist.
Help tell us how rock features formed and their relative ages

13. Which rock layer is the oldest?

14. Law of Superposition
The principle that a sedimentary rock layer is older than the layers above and younger than the ones below it.
Sedimentary rocks form when new sediments are deposited on top of old layers
Sedimentary rock layers are called beds
The boundary between two beds is called the bedding plane

16. Principle of Original Horizontality
Sedimentary rocks normally form in horizontal layers
Principle of original horizontality states that sedimentary rocks will stay in horizontal layers if left undisturbed.
No geologic forces acting on it.
Tectonic forces can overturn the sedimentary layers
If sed layers are not horizontal the law of superposition cannot be easily applied

17. Sedimentary Rock Features
Graded bedding
Cross-beds
Ripple marks

18. Superposition handout
Look at column A
What can you tell just by looking at this?
What two principles would apply to A?
Label the oldest rock layer and the youngest rock layer
Color in the layers based on rock type
Make a key of rock types between A and B

19. Exit Ticket 
Draw an example of graded bedding, ripple marks or Cross bedding

20. 3/15 Warm-Up
Explain the principle of original horizontality

21. Yesterday Recap Law of Superposition
Principle of original horizontality
Sedimentary rock features

22. Unconformities
Unconformity: a break in the rock record created when rock layers are eroded away or there is a gap in deposition
Shows that deposition stopped for a brief period of time
Rock has been eroded away by natural processes
Uplift and erosion
Creates a break in geologic time

23. 3 Types of unconformities
Nonconformity
Stratified rock is deposited on top of unstratified layers
Sediments may be eroded away
New sediment is deposited on the eroded material

24. 2. Angular conformity
Horizontal layers are deposited on tilted layers
Layers are folded or tilted
Then new layers are deposited on top

25. 3. Disconformity
Layers are NOT folded, tilted or eroded
Layers sink
Deposition of new layers continues on top
May look continuous but there is a large time gap

26. An unconformity is a gap in the rock record.
According to the law of superposition all rocks beneath an unconformity are older than the rocks above it.
An unconformity is a gap in the rock record.
Missing information

27. Law of Cross-cutting relationships
The principle that a fault or intrusion is younger than the layer it cuts through.
Fault: is a break or crack in Earth’s crust which shifts its position
Intrusion: igneous rock is formed when magma is injected into a rock which cools and solidifies

28. Superposition Handout
Look at B:
What is happening?
Order of oldest to youngest layers?
New rock type?  add to key
Look at C:
What type of unconformity is pictured?
Look at D:
What is pictured?

29. Section 1 Quiz
#1 what is the age of Earth? a years b. 6,000 years c Billion years d. 4.6 Billion years

30. #2 Sedimentary layers will remain horizontal if left undisturbed, this is based off of what idea? a. Law of Superposition b. Principle of original horizontality c. Stratification d. Uniformitarianism

31. #3 Determining the age of a rock layer based on surrounding objects is called? a. Absolute Age b. Assumed Age c. Relative Age d. uniformitarianism

32. #4 What is a break in the rock record caused by erosion and geologic activity known as? a. Unconformity b. A break c. A fault d. An intrusion

33. #5 A fault or intrusion is always older than the layers it cuts through, true or false? a. True b. False

34. Section 2: Determining Absolute Age

35. 3/16 Warm-up
Explain the principle of cross-cutting relationships

36. Absolute Age
Relative age only indicates that one rock formation is older or younger than another layer
Absolute age: the numeric age of a rock formation.
Scientist use different methods to measure absolute age

37. Rate of erosion Studying the rate of erosion
Ex: measuring the rate a stream erodes
Only practical for features that formed in the past 10,000 to 20,000 years
Niagara Falls
1.3 m eroded per year
For about 9,900 years

38. Rates of Deposition Calculating the rate of sediment deposition
Measure the amount of sediment deposited in an area over a long period of time = estimate age of rock
Average of 30 cm of sedimentary rock are deposited every 1,000 years
Not very reliable, provides just an estimate

39. Varve count
Varve: sedimentary layers that are deposited in an annual cycle.
Light colored bands of coarse sediment
Dark bands of fine sediment
Scientists can count the layers of varves and estimate the age
Generally form in glacial lakes
Summer large amounts of deposition occurs coarse grained
Winter smaller amounts of deposition occurs  finer grained

40. Radiometric Dating
A method of determining absolute age by comparing radioactive isotopes and stable isotopes
Radioactive isotopes have nuclei that emit particles and energy at a constant rate.
As large amounts of energy are released scientists use the natural breakdown of isotopes to date rocks

41. Half-Life
As atoms emit particles and energy the atom changes into a different isotope of the same element or a different element.
Original isotopes are called Parent isotopes
Newly formed isotopes are called Daughter isotopes
comparing the proportions of parent and daughter isotopes to determine absolute age
Half-life: the time required for half of the parent isotope to breakdown to for daughter isotope.
Ex: 10 parent isotope parent isotope left after 1 half life
Second half life 2.5 and so on

42. Radioactive Isotopes
Larger the percentage of daughter isotopes the older the rock is
Scientist use different radioactive elements when dating rocks
Uranium- used for dating rocks more than 10 million years old
As long as they contain Uranium
Argon-argon dating- used for dating rocks between 10,000 to 4.6 billion years old

43. Carbon Dating
Used to date younger rocks that are less than 70,000 years old
Wood, bones, shells and other material with in the rock layer may cause inaccurate dating
Carbon-14 dating or radiocarbon dating
Plants and animals contain carbon12 and carbon 14
Scientist compare the ratio of C12 and C14 in the sample

44. Exit Ticket 
Describe what a varve is and where they form