2. Chapter Menu Lesson 1: Relative Ages of Rocks
Lesson 2: Absolute Ages of Rocks
Click on a hyperlink to view the corresponding lesson.

3. 7.1 Relative Ages of Rocks uniformitarianism rock cycle clast
lithification
stratum
superposition
relative age

4. The Beginning of Modern Geology
7.1 Relative Ages of Rocks
The Beginning of Modern Geology
James Hutton was the first person to realize that one process formed rock and another process tore it down.

5. The Principle of Uniformitarianism
7.1 Relative Ages of Rocks
The Principle of Uniformitarianism
Scientists can observe the processes that are active today, and interpret what happened in the past.
Uniformitarianism states that the same Earth processes have been at work for a very long time.
Geological processes that are at work today were also at work in the past.
Geological processes are so slow that direct observation is not possible.

6. 7.1 Relative Ages of Rocks
The Rock Cycle
The rock cycle is a series of processes that make and change rocks through:
heating
melting
cooling
uplift
weathering
burial
increasing pressure
Metamorphosis

7. The Rock Cycle (cont.) 7.1 Relative Ages of Rocks
How are materials from the earth broken down?

8. 7.1 Relative Ages of Rocks
The Rock Cycle (cont.)

9. Three Major Types of Rocks
7.1 Relative Ages of Rocks
Three Major Types of Rocks
Igneous rocks
produced when magma solidifies
Metamorphic rocks
any rock that is put under extreme pressure or heat
Sedimentary rocks
form from compacted and cemented sediments

10. Sediment Formation and Layering
7.1 Relative Ages of Rocks
Sediment Formation and Layering
Sedimentary rocks form from preexisting rocks.
Four steps in the formation process:
Weathering
Transportation
Deposition
Lithification

11. 7.1 Relative Ages of Rocks
Weathering
Weathering is the physical or chemical breakdown of rocks into smaller pieces.
Physical weathering breaks down rocks without changing the mineral composition.
Chemical weathering changes the mineral composition of rocks.

12. 7.1 Relative Ages of Rocks
Weathering (cont.)

13. 7.1 Relative Ages of Rocks
Transportation
Transportation occurs when sediments move downhill to lower areas and come to rest.
Clasts, different-sized sediments such as large boulders to microscopic bits of rocks that require different amounts of force to move them.

14. 7.1 Relative Ages of Rocks
Deposition
Deposition occurs when sediment being transported by water, wind, or a glacier slows down or stops.
This usually happens in low areas called depositional environments.
Two characteristics are parallel, horizontal layers, and sorting.

15. 7.1 Relative Ages of Rocks
Lithification
Lithification occurs when older sediment layers become compacted beneath younger layers.
Mineral-rich liquids seep into the pore spaces between the sediment grains.
The water evaporates and the minerals are left behind to cement the grains together.

16. Superposition and the Fossil Record
7.1 Relative Ages of Rocks
Superposition and the Fossil Record
Layers of rocks are called strata.
Four principles help geologists study strata and interpret the rocks’ history.
Superposition
Original horizontality
Original lateral continuity
Cross-cutting relationships

17. Principle of Superposition
7.1 Relative Ages of Rocks
Principle of Superposition
In a stack of undisturbed sedimentary rock layers, the layers on the bottom were deposited before the layers on top.
Relative age tells how old something is when compared to something else.

18. Remaining Principles Original horizontality:
7.1 Relative Ages of Rocks
Remaining Principles
Original horizontality:
Rock layers are originally deposited in horizontal, or nearly horizontal, layers.
Original lateral continuity:
Sedimentary rocks form layers that cover large areas.
Cross-cutting relationships:
A layer or feature that cuts across other rock layers is younger than the layer(s) being cut.

19. Fossils and Relative Age
7.1 Relative Ages of Rocks
Fossils and Relative Age
Geologists keep track of which fossils came from which strata and apply the principle of superposition.
Fossil occurrences in layers are used to confirm or assign relative ages to rock strata.
Steno’s Principles

20. C original lateral continuity D uniformitarianism
7.1 Relative Ages of Rocks A B C D
What principle states that processes at work today are the same processes that occurred in Earth’s past?
A superposition
B relative age
C original lateral continuity
D uniformitarianism
Lesson 1 Review

21. What type of rock is formed when put under extreme pressure or heat?
7.1 Relative Ages of Rocks A B C D
What type of rock is formed when put under extreme pressure or heat?
A igneous
B metamorphic
C strata
D sedimentary
Lesson 1 Review

22. What process slows or stops sediments in low areas of the landscape?
7.1 Relative Ages of Rocks A B C D
What process slows or stops sediments in low areas of the landscape?
A deposition
B lithification
C weathering
D transportation
Lesson 1 Review

23. End of Lesson 1

24. 7.2 Absolute Ages of Rocks
isotope
radioactive decay
half-life

25. 7.2 Absolute Ages of Rocks
What is Earth’s Age?
Scientists discovered and used a natural “clock” to date the age of Earth, meteorites, and the moon.
Scientists used this natural clock to determine the age of bog bodies.

26. 7.2 Absolute Ages of Rocks
Atoms and Isotopes
Atoms are the microscopic building blocks of all matter on Earth.

27. Atoms and Isotopes (cont.)
7.2 Absolute Ages of Rocks
Atoms and Isotopes (cont.)
An isotope is the term for atoms of an element that have the same number of protons, but a differing number of neutrons.
Carbon isotopes—carbon-12, carbon-13, carbon-14—have 6, 7, or 8 neutrons.

28. 7.2 Absolute Ages of Rocks
Radioactive Decay
Radioactive decay occurs when an unstable nucleus changes into another nucleus by emitting particles and energy.

29. Parent and Daughter Isotopes
7.2 Absolute Ages of Rocks
Parent and Daughter Isotopes
The isotope that undergoes radioactive decay is the parent isotope.
The stable form of the element that forms is the daughter isotope.

30. 7.2 Absolute Ages of Rocks
Half-Life
Parent isotopes decay into daughter isotopes at a constant rate—the decay rate.
The half-life of an element is the calculated length of time it takes for half a specific amount of a parent isotope to decay.

31. 7.2 Absolute Ages of Rocks
Half-Life (cont.)

32. 7.2 Absolute Ages of Rocks
Radiometric Dating
Scientists use radiometric dating to calculate absolute ages of rocks and minerals.
Comparing the amount of parent to daughter material determines the number of half-lives the material has been through.
Igneous rock is most commonly used for radiometric dating.

33. The Absolute Age of Earth
7.2 Absolute Ages of Rocks
The Absolute Age of Earth
Rock grains from continental shields—where the oldest rocks on Earth occur—are estimated to be 4.0 to 4.4 billion years old.

34. Meteorites and the Moon
7.2 Absolute Ages of Rocks
Meteorites and the Moon
Scientists used radiometric dating to determine the ages of meteorites and the Moon.
The closeness of calculated ages of Earth, the Moon, and meteorites helps confirm that the entire solar system formed at the same time.

35. The isotopes of an element have a different number of what? A protons
7.2 Absolute Ages of Rocks A B C D
The isotopes of an element have a different number of what?
A protons
B neutrons
C electrons
D atoms
Lesson 2 Review

36. A the isotopes of an element may be stable or unstable
7.2 Absolute Ages of Rocks A B C D
What important feature of radioactive decay has allowed geologists to date Rocks?
A the isotopes of an element may be stable or unstable
B the nucleus gains or loses protons
C parent isotopes decay into daughter isotopes
D the decay occurs at a constant rate
Lesson 2 Review

37. What do scientists use to measure the absolute age of a rock?
7.2 Absolute Ages of Rocks A B C D
What do scientists use to measure the absolute age of a rock?
A radiometric dating
B amount of carbon in the rock
C absolute dating
D relative dating
Lesson 2 Review

38. End of Lesson 2

39. Chapter Resources Menu
Chapter Assessment
California Standards Practice
Concepts in Motion
Image Bank
Science Online
Interactive Table
Virtual Lab
BrainPOP
Click on a hyperlink to view the corresponding feature.

40. How can the rounded peaks of older mountain ranges be explained?
A erosion
B weathering
C uplift
D deposition
Chapter Assessment 1

41. A B C D
What term describes the physical or chemical breakdown of rocks into smaller pieces?
A deposition
B erosion
C lithification
D weathering
Chapter Assessment 2

42. D original horizontalityB C D
What principle states that the bottom layers of sedimentary rocks were deposited before the top layers?
A lithification
B uniformitarianism
C superposition
D original horizontality
Chapter Assessment 3

43. What type of rock is most commonly used in radiometric dating? B C D
What type of rock is most commonly used in radiometric dating?
A metamorphic
B igneous
C sedimentary
D minerals
Chapter Assessment 4

44. A B C D
What term describes time it takes for a sample of a radioactive isotope to decay to half its original mass?
A absolute age
B half-life
C radiometric dating
D relative age
Chapter Assessment 5

45. B metamorphic rock formation C igneous rock formation D the rock cycle
SCI 4.c A B C D
What process includes heating, melting, cooling, uplift, weathering, and increasing pressure?
A sediment formation
B metamorphic rock formation
C igneous rock formation
D the rock cycle
CA Standards Practice 1

46. What does the principal of original lateral continuity state?
SCI 4.c A B C D
What does the principal of original lateral continuity state?
A layers on the bottom are deposited before layers on the top
B sediments are deposited horizontally
C sedimentary rocks form layers that cover large areas
D sediments always remain horizontal
CA Standards Practice 2

47. Which type of rock is the most useful for relative dating? A igneous
SCI 4.c A B C D
Which type of rock is the most useful for relative dating?
A igneous
B sedimentary
C magma
D metamorphic
CA Standards Practice 3

48. Which describes a daughter isotope? A decays into a parent isotope
SCI 4.d A B C D
Which describes a daughter isotope?
A decays into a parent isotope
B is an unstable form of the parent isotope
C is the result of parent isotope decay
D is heavier than its parent isotope
CA Standards Practice 4

49. What percentage of parent isotope remains after 2 half-lives? A 75
SCI 4.d A B C D
What percentage of parent isotope remains after 2 half-lives?
A 75
B 30
C 37.5
D 25
CA Standards Practice 5

50. Concepts in Motion 1

51. Concepts in Motion 2

52. Image Bank

53. Interactive Table
Steno’s Principles

54. End of Resources