1. Mr. Ahearn Earth Science 2010
Geologic History
Mr. Ahearn
Earth Science 2010

2. Discovering Earth’s History
Rocks record geological events and changing life forms of the past
We have learned that Earth is much older than anyone had previously imagined.
The surface and interior have been changed by the same geological processes that happen today

3. Discovering Earth’s History
Principle of Uniformitarianism:
The forces and processes happening today have been going on for a long time

4. Key Principles Tells us the sequence in which events occurred
Relative Dating
Tells us the sequence in which events occurred
Law of Superposition
In sedimentary rocks, each bed is older than the one above it and younger than the one below it

5. Law of Superposition
Younger Layers→
Older Layers→

6. Ordering the Grand Canyon’s History
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7. Relative Dating Principles
 Principle of Original Horizontality
• The principle of original horizontality means that layers of sediment are generally deposited in a horizontal position.

8. Disturbed Rock Layers
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9. Relative Dating Principles
 Cross-Cutting Relationships
• The principle of cross-cutting relationships states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected.
 Inclusions
• Inclusions are rocks contained within other rocks.
• Rocks containing inclusions are younger than the inclusions they contain.

10. Applying Cross-Cutting Relationships
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11. Formation of Inclusions
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12. Relative Dating Principles
 Unconformities
• An unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed.
• An angular unconformity indicates that during the pause in deposition, a period of deformation (folding or tilting) and erosion occurred.

13. Formation of an Angular Conformity
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14. Relative Dating  Unconformities
• A nonconformity is when the erosional surface separates older metamorphic or intrusive igneous rocks from younger sedimentary rocks.
• A disconformity is when two sedimentary rock layers are separated by an erosional surface.

15. A Record of Uplift, Erosion, and Deposition
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16. Complete Questions #1-15 Review Book p. 119-121

17. Correlation of Rock Layers
 Correlation is establishing the equivalence of rocks of similar age in different areas.

18. Correlation of Strata at Three Locations
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19. Fossils: Evidence of Past Life
Remains or traces of prehistoric life
Mainly found in sedimentary rock

20. Fossils: Evidence of Past Life
 The type of fossil that is formed is determined by the conditions under which an organism died and how it was buried.
 Unaltered Remains
• Some remains of organisms—such as teeth, bones, and shells—may not have been altered, or may have changed hardly at all over time.

21. Fossils: Evidence of Past Life
 Altered Remains
• The remains of an organism are likely to be changed over time.
• Fossils often become petrified or turned to stone.
• Molds and casts are another common type of fossil.
• Carbonization is particularly effective in preserving leaves and delicate animals. It occurs when an organism is buried under fine sediment.

22. Fossils: Evidence of Past Life
 Indirect Evidence
• Trace fossils are indirect evidence of prehistoric life.
 Conditions Favoring Preservation
• Two conditions are important for preservation: rapid burial and the possession of hard parts.

23. Types of Fossilization
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24. Fossils: Evidence of Past Life
 The principle of fossil succession states that fossil organisms succeed one another in a definite and determinable order. Therefore, any time period can be recognized by its fossil content.
 Index fossils are widespread geographically, are limited to a short span of geologic time, and occur in large numbers.

25. Fossils: Evidence of Past Life
 Interpreting Environments
• Fossils can also be used to interpret and describe ancient environments.

26. Overlapping Ranges of Fossils
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27. Complete Questions # 15-21 Review Book p. 122-124

28. The Geologic Time Scale

29. Precambrian All time between origin of Earth & 570 mya
Rocks lack fossils
Igneous & M/M
Animals lacked hard parts
Stromatolites

30. Paleozoic: Cambrian
                                 
walking trilobite ©2000
Most of the major groups of animals first appear in the fossil record.
"Cambrian Explosion“
Trilobite: index fossil
Mostly marine animals

31. Paleozoic: Ordovician
Increase in number & KINDS of animals
All life in oceans
Index fossil: graptolite
Early molluscs
Ended w/ Taconic Orogeny
Green Mountains & Taconics (NY &VT)

32. Paleozoic: Silurian Similar life to Ordovician Plants on land
Club mosses

33. Paleozoic: Devonian “Age of Fishes” Warm oceans Land plants multiplied
True ferns
Seed plants
First forests
Deer Isle, Maine

34. Paleozoic: Carboniferous
Huge freshwater swamps
Coal beds along Mississippi river
1st reptiles appeared
More insects
“The age of Cockroaches”

36. Carboniferous Rocks Back to Rocks of Ages Back to Rocks of Ages
Back to Rocks of Ages
Mississippian and Pennsylvanian Rocks
Mississippian and Pennsylvanian Rocks
Mississippian and Pennsylvanian Rocks
                                                                                                
                                                                                                
                                                                                                
Carboniferous Rocks
                                                                                                
                                                                                                
                                                                                                

37. Folded Carboniferous Coal Beds

38. Paleozoic: Permian Dry Climate Inland coral reefs created
Layers of evaporites
Inland coral reefs created

39. Mesozoic: Triassic Extinction of many marine animals More gymnosperms
Trilobites
More gymnosperms
Earliest dinosaurs

40. Mesozoic: Jurassic
Earliest birds & mammals

41. Mesozoic: Cretaceous

42. Mesozoic: Cretaceous Earliest flowering plants
Climax & extinction of dinosaurs
1st placental mammals

43. Mass Extinction

44. Cenozoic: Tertiary/Quaternary
Early warm
Later ice age
Grand Canyon formed
Modern mammals, animals & plants

45. Complete Questions # 22-51 Review Book p. 129-132

46. The End Or is it our future?