1. The Rock and Fossil Record
Chapter 15
Time Marches On
Looking at Fossils
Earth’s Story and Those Who First Listened
Relative Dating: Which Came First?
Absolute Dating: A Measure of Time

2. Terms You Must Know Fossil Uniformitarianism Trace fossil
Mold
Cast
Index fossil
Geologic time scale
Eon
Era
Period
Epoch
extinction
Uniformitarianism
Catastrophism
Paleontology
Relative dating
Superposition
Geologic column
Unconformity
Absolute dating
Isotope
Radioactive decay
Radiometric dating
Half-life

3. Earth’s age =4,600,000,000 or 4.6 billion years old

4. Grand Canyon: history revealed
Reading this rock book shows:
periods of mountain building
advancing and retreating shallow seas
evolution of faunas
Nearly 2 billion years of history are preserved in the rock layers of the Grand Canyons 2 km depth.

5. Relative Geologic Time Scale
The relative geologic time scale has a sequence of
eons - largest divisions of geologic time
eras – second largest division
periods – third largest division
epochs – fourth largest division
but no numbers indicating how long each time frame occurs occurred

6. Geologic Time Scale
Large divisions based on characteristics of fossils
Paleozoic Era – early life dominated by invertebrate animals
Mesozoic Era – middle life dominated by reptiles
Cenozoic Era – recent life dominated by mammals

8. What marks the close of one geologic time frame and the dawn of another?
Either there is a mass extinction or a higher order life form begins to dominate or both events occur!
Extinction = there is a death of every member of the species – they are permanently gone!

9. Geologic Time Scale
The discovery of radioactivity near the end of the 1800s allowed absolute ages to be accurately applied to the relative geologic time scale
The geologic time scale is a dual scale
a relative scale (near accurate)
and an absolute scale (accurate)

10. Changes in the Concept of Geologic Time
The concept and measurement of geologic time has changed through human history!
James Ussher ( ) in Ireland
calculated the age of Earth based on recorded history and genealogies in Genesis
he announced that Earth was created on October 22, 4004 B.C.
a century later it was considered heresy to say Earth was more than about 6000 years old

11. During the 1700s and 1800s Earth’s age was estimated scientifically
Georges Louis de Buffon ( ) calculated how long Earth took to cool gradually from a molten beginning
used melted iron balls of various diameters
he estimated Earth was 75,000 years old
Others used rates of deposition of various sediments and thickness of sedimentary rock in the crust
gave estimates of <1 million
to more than 2 billion years
Or the amount of salt carried by rivers to the ocean and the salinity of seawater
John Joly in 1899 obtained a minimum age of 90 million years

12. So what is today’s date? Today is the ____ day, __first__ month,
__second__ decade,
__21st__ century,
__third__ millennium,
__holocene__ epoch,
__quaternary__ period,
__cenozoic__ era and the __phanerozoic__eon.

13. Why did the dinosaurs all die?
*We only have theories and fossils to guide us!
Ideas: meteor hit, asteroid strike, volcanic eruptions, earthquakes, wildfires, drought, flood, famine, sea level rise, glacial advance, continental drift/climate change, boredom, over hunting…

14. Fossils – remains of dead plant or animal that have been preserved
Fossil facts:
-they are rare due to rock cycle and mining processes
-they are usually found in sedimentary rock
-casts are made for museums & sale
Casts are made from a hollow mold
-vertebrates make the best fossils (have hard body parts)
-invertebrates, have too many soft body parts

15. Types of Fossils
1. Plain fossils are Mother Nature’s cast copy of a formerly living organism made from layers of sediment that have turned into stone = sedimentary rock!

16. 2. Imprint fossils are flat carbonaceous films of a formerly living organism such as a fish or plant. They are 2D.

17. 3. Frozen fossils are nearly whole organisms preserved in glacial ice
3. Frozen fossils are nearly whole organisms preserved in glacial ice. Little decay occurs due to freezing temperatures and few bacteria. These are 3D.

18. 4. Petrified fossils used to be bone or wood that has been replaced by layers of sediment to create a stone copy of the once living species. The process is known as petrification.

19. 5. Amber is hardened tree sap or rosin that has mineralized with heat, pressure and time. Organisms trapped in the tree sap are perfectly preserved. They are usually small creatures like insects, lizards or frogs.

20. 6. Trace fossils are those fossils that are naturally preserved evidence of some animal activity such as footprints, burrows and coprolites. They are not the organism itself.

21. Mold vs. Cast Cast – object created when sediment fills mold
Mold – hollow cavity created by fossil cast
Latex molds are used to create fake cast fossils for museum displays, schools, stores…

22. Fossil type
Advantage
Disadvantage
Plain fossil
3D, see size dimensions, near exact copy
Mineral replacements, hard body parts only
Imprint
See perfect size dimensions, flat copy 2D
Frozen fossil
3D, real organism
Thawing would destroy fossil
Petrified fossil
Rock copy, not the real deal
Amber
3D, real organism, gemstone value
Cutting/breaking open would destroy fossil and valuable gemstone, only small organisms
Trace fossil
Tells us about their activity
Not the organism itself

23. Uniformitarianism
1. Uniformitarianism – the notion that the geologic processes actively forming Earth today are the same that have been active in the past and are unchanged
Two main processes are erosion and deposition
developed in 1788, by geologist James Hutton
Studied rock formations for 30 plus years in England and Scotland
Now a widely held principle today, in part thanks to the addition of Charles Lyell’s research and writings in the 1830’s

24. Catastrophism
2. Catastrophism – opposing idea to Hutton’s – states that the Earth’s features were created suddenly through catastrophes
Proposed by Georges Cuvier ( )
Dominated European geologic thinking
Biblical events were referenced
Was used to explain extinctions

25. People To Know
James Hutton
Charles Lyell
Georges Cuvier

26. Siccar Point Hutton’s theories sparked a scientific debate
In Hutton’s time, people believed that the Earth was only a few thousand years old.
What Hutton proposed could not happen in just a few thousand years
He formed his theories by observing the geologic processes at Siccar Point
Deposition and folding were observed

27. Idea of Modern Geology???
Modern scientists like Stephen Gould have challenged Lyell’s uniformitarianism.
Today scientists believe that catastrophes do at times play an important role in shaping Earth’s history.
Most geologic change is gradual and uniform but catastrophes have caused geologic change.
Ex. Craters formed due to asteroids and comets

28. Unconformity
3. Unconformities – are irregularities found in a geologic column of soil, these irregularities are due to either erosion or missing deposition.
Unconformity is a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

29. Unconformity at Siccar Point

30. Unconformity
When a geologists finds an unconformity, they must question whether the “missing layer” was never present or whether is was somehow removed
Nondeposition- stopage of deposition when a supply of sediment is cut off
Erosion can create unconformities.

31. 3 Types of Unconformity Disconformities Nonconformities
Most common
Part of a sequence of parallel rock layers is missing
Nonconformities
Angular unconformities

32. A. Disconformities – occurs when erosion carries away deposition, which stops for a while, then deposition begins again What’s missing?

33. Disconformity
Disconformities are much harder to recognize in the field, because often there is no angular relationship between sets of layers. Disconformities are usually recognized by correlating from one area to another and finding that some strata is missing in one of the areas.

34. B. Nonconformities – non-layered igneous intrusions (lava) are pushed up from inside the Earth and are eroded in the upheaval, while deposition occurs on top, hiding the top eroded area What’s missing?

35. Nonconformity
Nonconformities occur where rocks that formed deep in the Earth, such as intrusive igneous rocks or metamorphic rocks, are overlain by sedimentary rocks formed at the Earth's surface. The nonconformity can only occur if all of the rocks overlying the metamorphic or intrusive igneous rocks have been removed by erosion.

36. Nonconformity
Notice that there is an "intersection" of a vertical rock butting up against a horizontal sock. In an unconformity, it is two of the same type of rock (e.g. sedimentary & sedimentary). A nonconformity is two layers of different types (e.g. igneous & sedimentary).

37. C. Angular unconformities – occurs when rock layers have been tilted or folded and then eroded before more horizontal deposition happens on top What’s missing?

38. Angular unconformity
Angular unconformities are easy to recognize in the field because of the angular relationship of layers that were originally deposited horizontally.

39. Example of an Unconformity
Tilted sandstone and siltstone below, conglomerate above

40. Listen for unconformities in this Queen hit from 1975!
Class Activity:
Listen for unconformities in this Queen hit from 1975!
Use the Vis-à-vis to denote changes in “layers” of the song (geologic column). Use a star to denote the unconformity!

41. Important things to remember:
Law of superposition - states that the older rocks lie beneath younger rocks and fossils in undisturbed areas
Geologic column - a section of rock layers pieced together using the law of superposition and filling in the mysteries of geologic time
Index fossils – fossilized organisms that are used to help date surrounding organisms and rock layers, they are known reference points in the geologic time scale

42. Two ways to date rocks & fossils
1. Relative dating
Using a set of principles to put rocks in their proper sequences of formation
2. Absolute dating
Using radioactive decay to determine the exact age of rocks

43. Relative-Dating Principles
Relative dating is any method of determining whether an event or object is older or younger than other events or objects.
Apply:Law/Principle of Superposition
Oldest on bottom, youngest on top
Chattanooga Shale, TN

44. Relative Dating Relative dating
Can only be used when the rock layers have been preserved in their original sequence
Helps scientists determine whether one fossil is older than the other

45. Disturbing Forces
Not all rock formations are arranged with the oldest layers on the bottom.
Natural forces can fold, tilt, break, or remove parts of the rock layer
Geologists use a geologic column to help them
Relative dating assumes that if rock layers are not horizontal, then something must have disturbed them after they formed.

46. Cross-cutting Relationships
A dark-colored dike has intruded into older light colored granite: the dike is younger than the granite
North shore of Lake Superior, Ontario Canada

47. Cross-cutting Relationships
A small fault displaces tilted beds: the fault is younger than the beds
Templin Highway, Castaic, California

48. Absolute Dating: any method of measuring the exact age of an event or object in years Most common:based on Radioactive Decay
Parent
daughter
Why does it work?
1. The decay rate is CONSTANT,
independent of external conditions in the earth.
2. The daughter/Parent ratio can be precisely measured.

49. Radioactive Decay
The process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element.
Sounds great but what is an isotope?
An isotope is an atom that has the same number of protons (atomic #) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass)

50. How does it work? What does this have to do with the age of rocks?
Unstable isotope is called parent isotope
The stable isotope produced by radioactive decay is the daughter isotope.
Decay is constant!
The more daughter isotope- the older the rock!

51. Radiometric dating
A method of determining the age of an object by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope
Really just a ratio of parent material to daughter material.

52. Half-life – the time required for one-half of the radioactive nuclei in a sample to decay

53. Types of radiometric dating
Potassium-argon method
K-40 half-life 1.3 billion years
Decays into argon and calcium
Used to date rocks older than 100,00 years old
Uranium-lead method
U-238 half-life 4.5 billion years
Decays into lead-206
Used for rocks more than 10 million years old
Rubidium-strontium method
Rb-87 half-life 49 billion years
Decays into strontium-87
Carbon-14 method

54. Dating with carbon-14 (radiocarbon dating)
-Half-life of only 5730 years
-Used to date very recent events
-Carbon-14 is produced in the upper atmosphere
-Useful tool for anthropologists, archeologists, and geologists who study very recent Earth history
-Carbon-14 is continuously created in the atmosphere by cosmic radiation.
-Plants absorb C-14 directly through their leaves in the form of carbon dioxide
-Animals take in C-14 indirectly when they eat plants
-When an organism dies, it stops absorbing new C-14 and its radiocarbon “clock” is set.

55. Geometric Radioactive Decay
In radioactive decay, during each equal time unit, one half-life, the proportion of parent atoms decreases by 1/2

56. Absolute Dating
Radiometric dating is the most common method of obtaining absolute ages
calculated from the natural rates of decay of various natural radioactive elements present in trace amounts in some rocks
Other methods?
Tree ring counting (use overlapping layers from several trees)
Varves (annually produced layer of sedimentary rock)
Ice cores

57. Tree-Ring Dating Method
In cross-dating, tree-ring patterns are used from different trees, with overlapping life spans

58. Sources of Uncertainty
Closed system is needed for an accurate date
neither parent nor daughter atoms can have been added or removed from the sample since crystallization
If leakage of daughters has occurred
it partially resets the radiometric clock and the age will be too young
If parents escape, the date will be too old
Most reliable dates use multiple methods

59. Sources of Uncertainty
Dating techniques are always improving
Presently measurement error is typically <0.5% of the age, and even better than 0.1%
A date of 540 million might have an error of ±2.7 million years or as low as ±0.54 million

60. Mass Spectrometer

61. Natural Selection and the Theory of Evolution
-some scientists believe the Earth is older than previously thought because of the fossil record
-the English naturalist famous for his voyages and studies is Charles Darwin

62. -in 1831, at the age of 22, Darwin took a five year voyage on a ship known as the HMS Beagle; he was the ship’s naturalist -Darwin continued taking mapping and collecting expeditions to the Galapagos Islands

64. Galapagos Critters!

65. -in 1836, Darwin came home for 22 years and studied his findings -Darwin developed the idea that organisms in nature “struggle for existence” (meaning all living things must compete with one another for life, food, shelter, space and mates in order to survive)

66. -in 1859, Darwin published a book explaining the discoveries of his and fellow scientists (Alfred Wallace) entitled On the Origin of Species by Means of Natural Selection

67. -some of Darwin’s ideas came from his experiments when he selected the specific traits of offspring and then bred selected farm animals to see the outcomes; this is known as artificial selection.

69. A mule is the offspring of a male donkey and a female horse (The much rarer offspring of a male horse and a female donkey is called a hinny.) They are sterile due to chromosome differences!
Horse (64) + Donkey (62) = Mule

70. -Darwin thought that a similar mechanism occurred in nature; the mechanism for change in an organism, with favorable variations for a particular environment he termed natural selection (meaning those without “good” genes for a specific environment are more likely to die and not pass on their genes)

71. The tale of the peppered moths evolution

72. Examples of how organisms become naturally selected for:
They copy the exact look of another organism – mimicry
They are colored to match their environment or can change colors to match their habitat – camouflage
They grow structures to avoid predation and/or have for defense – bodily additions

73. Camouflage Examples

74. Mimicry Examples

75. Structural Adaptations Examples

77. 4. They become able to avoid death usually caused by chemicals – pesticide and antibiotic resistance Ex. DDT

79. Ex. Penicillin resistant bacteria

80. How to prevent antibiotic resistant infections
1. Don’t demand a prescription of antibiotics from your doctor, unless he or she has diagnosed your affliction as a bacterial infection that requires it. 2. Take all of the antibiotics as prescribed, even if the symptoms subside Never share your antibiotics with friends or family, even if you are 100% sure that they have the same infection. Let your doctor do the exam and write a new prescription.

81. Comparing the structural details of features found in different but related organisms reveals a basic similarity. Ex. forelimb of mammals - human arm, cat forelimb, whale front flipper, bat wing. Although function is quite different, they appear to be so similar structurally
Homologous structures

83. All vertebrate embryos have segmented muscles, gill pouches, a tubular heart without left & right sides.
Embryological development

85. How evolution affects whole populations

86. Lyell and Darwin Charles Darwin and Charles Lyell were good friends.
Darwin accepted and supported uniformitarianism
Darwin had read Lyell’s book Principles of Geology before his famous 1831 voyage on HMS Beagle
Despite being friends, Lyell did not embrace Darwin’s theories of natural selection.
Much later, Lyell finally accepted Darwin’s theories.

87. Jamey Johnson’s “In Color”
I said, Grandpa what’s this picture here It’s all black and white and ain’t real clear Is that you there, he said, yeah I was eleven Times were tough back in thirty-five That’s me and Uncle Joe just tryin’ to survive A cotton farm in the Great Depression And if it looks like we were scared to death Like a couple of kids just trying to save each other You should have seen it in color This one here was taken overseas In the middle of hell in nineteen forty-three In the winter time you can almost see my breath That was my tail gunner ole’ Johnny McGee He was a high school teacher from New Orleans And he had my back right through the day we left

88. And if it looks like we were scared to death Like a couple of kids just trying to save each other You should have seen it in color A picture’s worth a thousand words But you can’t see what those shades of gray keep covered You should have seen it in color This one is my favorite one This is me and grandma in the summer sun All dressed up the day we said our vows You can’t tell it here but it was hot that June That rose was red and her eyes were blue And just look at that smile I was so proud

89. That’s the story of my life Right there in black and white And if it looks like we were scared to death Like a couple of kids just trying to save each other You should have seen it in color A picture’s worth a thousand words But you can’t see what those shades of gray keep covered You should have seen it in color You should have seen it in color