1. The Rock and Fossil Record
Geologic Time
The Rock and Fossil Record

2. Geologic Time Scale
time
divisions
Geologists use different _______ ________ to keep track of Earth’s history.
These divisions are based on:
Type of ____________ present during the time period
Type of ____________ changes occurring at the time.
Geologic Time Scale – a record of Earth’s history, beginning 4.6 bya, that shows events, time units, and ages.
life forms
geologic

3. Geologic Time Scale
There are three types of subdivisions of geologic time:
______ – major subdivisions of time based on differences in life-forms.
__________ – subdivisions of eras based on types of life and geologic events (mountain building or plate movements).
_________ – subdivisions of periods based on types of life and geologic events. (Epochs are found in the Cenozoic Era alone because the fossil records and rock layers are more complete for this time.)
ERA
Period
Epoch

4. Era
Period
Epoch
Phanerozoic Eon
Cenozoic
Quaternary
Recent
Pleistocene
Neogene
Pliocene
Miocene
Paleogene
Oligocene
Eocene
Paleocene
Mesozoic
Cretaceous
Jurassic
Triassic
Paleozoic
Permian
Pennsylvanian
Mississippian
Devonian
Silurian
Ordovician
Cambrian
Precambrian Time

6. Earths Story and Those Who First Listened.
uniformitarianism
Scientists use ____________________ to interpret the past and predict the future.
James Hutton 1795 – “Theory of Earth”
The _______ is the key to the _____.
Things that happened now must have happened in the past.
present
past

7. Uniformitarianism versus Catastrophism
Uniformitarianism – equal to slow change
Catastrophism – equals quick sudden changes.
Which is right?
A little of both.

8. Relative Dating - Superposition
Here’s a stack of newspapers collecting dust in the living room.
Everyday as the paper is read it is put in the pile.
Someone comes to you and asks about an article from last week.
Where do you look?

9. Relative Dating? Which came first?
Which layer is older?
Geologists use relative dating to determine the ____________ of objects.
Principle of Superposition – younger layers lie above older layers in an undisturbed sequence of rocks. A
relative age C B A

10. The Principle of Superposition
In an undisturbed layer of rock the oldest rock is on the ___________ and the youngest is on the _______.
BOTTOM
TOP

11. The Principle of Superposition
Exceptions to the Principle include tectonic forces acting on the rocks to _______, tilt, fault, or __________ rock layers.
MOVE
ERODE

12. Original Horizontality: sedimentary layers are initially deposited in horizontal layers
The forces of reality beat up on the earth and break it into small pieces, which then wash down rivers to the ocean and settle out on the seafloor. In horizontal layers.

13. Relative Dating
Used by geologist to determine the order of events and the relative age of rocks by their ___________ in the stack.
POSITION

14. Relative Dating
This image shows a stack of rocks with 3 different types of rock and one fault.
Which is the oldest?

15. Relative Dating
Here’s the sequence: A, B, fault, C C B B A A

16. Unconformities Rock layers are a record of past geologic events.
Most are ____________ because they are missing layers.
If sediment stops being deposited and _________ goes to work removing material then you will have a gap in the record.
These gaps are called _________________.
INCOMPLETE
EROSION
UNCONFORMITIES

17. Angular Unconformities

18. Angular Unconformities

19. Angular Unconformities

20. Disconformity
No obvious evidence of missing rock layers except for an __________ surface caused by erosion.
UNEVEN

21. Nonconformity
When sedimentary rock layers form above ____________ or intrusive ___________ rock layers.
The metamorphic or igneous rock is uplifted and eroded.
Sedimentary rocks are then deposited on top.
METAMORPHIC
IGNEOUS

22. Nonconformity
Arrow points to contact of Cambrian Tapeats Sandstone on Precambrian Vishnu Schist.

23. Cross-cutting relationships: the thing being cut is ________ than the thing doing the cutting
OLDER
You can’t cut it if it isn’t there.
Igneous intrusions:
Dikes, Sills, Batholiths, Laccoliths

24. Cross-cutting Relationships

26. Fossils

27. Fossils
Definition:
Fossil – the remains, imprints, or traces of once-living organisms, usually preserved in rock, that tell us when, where, and how those organisms lived.

28. Fossils
Fossils help scientists determine when and where plants and animals lived.
Also, how they lived.

29. Fossil Formation Necessary Conditions: Quick Burial Hard Parts
The body of a dead organism must be protected from scavengers and microorganisms.
________________ (sediments from floods, landslides, etc.)
________________ (bones, shells, or teeth)
_________________________ Fossils typically do not withstand the heat and pressure involved in forming igneous and metamorphic rocks.
Limestone, Shale, Sandstone are examples
Quick Burial
Hard Parts
Sedimentary Rocks
NEARLY ALL FOSSILS ARE FOUND IN SEDIMENTARY ROCK

30. Fossil in Virginia Appalachian Plateau Valley & Ridge Coastal Plain
Why not the Blue Ridge and Piedmont?

31. Fossil in Virginia
Era
Period
Epoch
Cenozoic
Quaternary
Recent
Pleistocene
Tertiary
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Mesozoic
Cretaceous
Jurassic
Triassic
Paleozoic
Permian
Pennsylvanian
Mississippian
Devonian
Silurian
Ordovician
Cambrian
Precambrian Time
Paleozoic, Mesozoic, and Cenozoic fossils are found in Virginia
544 mya – present
Paleozoic
Mesozoic
Cenozoic

32. Petrified Remains
Some or all of the original materials in the remains have been replaced by minerals.

33. Carbonaceous Films
The tissues of most organisms are made of compounds that contain carbon.
Sometimes that’s all that is left.
Pressure and heat force gases and liquids from the body and leave an outline of the body.

34. Carbonaceous Films
Swamps and deltas where large amounts of plant matter are areas in which these fossils are found.

35. Molds and Casts
Seashells or other hard parts fall into soft sediment such as mud and get buried.
Compaction and sedimentation turn the sediments to rock.
Pores in the rock let water and air reach the object and allow it to decay.
The resulting void is called a mold.
Other sediments may fill the mold and solidify into a cast.

36. Original Remains Sometimes the original remains are preserved.
Insects trapped in amber (crystallized resin)
Ice men, mammoths
Tar Pits

37. Trace Fossils Fossilized tracks or other evidence of animal activity.
Dino-tracks
Coprolites

38. Index fossils
Species inhabit Earth for a period of time before evolving into new species or dying out.
Paleontologists use animals that exist for a short time period as index fossils.
Index fossil – species that existed on Earth for a relatively ______ period of time, were _________, were ___________ geographically.
short
numerous
wide-spread

39. Index fossils
Index fossils are used to determine the age of rock layers.
200
Life Span (mya) A
300 B
400 C
500

40. Fossils and Ancient Environments
Fossils also indicate the ______________of an area long ago.
Remember Antarctic rocks contain fossils of tropical plants
environment

41. Fossils and Ancient Environments
Most VA fossils are of __________________
Brachiopod fossils indicate a shallow sea environment.
Brach’s are found in the mountains of Virginia
What can you conclude from this?
marine organisms

42. Absolute Dating Absolute time places a _____________ age on an event.
numerical
Absolute time places a _____________ age on an event.
_________________ is used to determine the absolute age of rocks.
Radioactive decay

43. Radiometric Dating
Radiometric Dating – determining the age of a material by comparing the ratio of the ___________ (undecayed) material to the ___________ (decayed) material.
Example: A rock has an isotope that takes 10,000 years to decay into half of the parent material. The half-live is 10,000 years. Scientist examine the rock and find exactly half of the material is “parent” material and half is “daughter” material. Then the age of the rock has to be _______________ years.
parent
daughter
10,000

44. C