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Earth’s Geologic History Aim: How do we determine the chronology of earth’s events?

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Presentation on theme: "Earth’s Geologic History Aim: How do we determine the chronology of earth’s events?"— Presentation transcript:

1 Earth’s Geologic History Aim: How do we determine the chronology of earth’s events?

2 Vocabulary Uniformitarianism Relative Age Horizontality Superposition Chronology Intrusions Extrusions Inclusions Correlation Unconformity Index fossils

3 Uniformitarianism Processes going on today also took place in the past Ex. - Weathering, erosion, deposition, earthquakes, volcanoes The processes layering sedimentary rocks today also occurred in the past

4 Relative Age of Layers Original Horizontality – sediments are deposited in parallel, horizontal layers. Superposition- undisturbed layers will have the oldest on the bottom and youngest on top

5 How can the older layers end up on top? Faulting Folding Crustal Uplift

6 Intrusions Magma forcing its way into cracks and solidifying into igneous rock The surrounding rock is older than he intrusion.

7 What is the sequence of events? 1.Formation of sedimentary rock layers 3. Intrusion of igneous magma into the sedimentary rock 4. Contact metamorphism where magma meets sedimentary rock layers 2. Movement / uplift along the fault

8 Extrusions Magma that surfaces and solidifies The rock layers below the extrusion are older than the extrusion. Another layer of deposition can lay more sedimentary rock above the extrusions… which would then be younger than the extrusion

9 Order of events:

10 Name them oldest to youngest:

11 1 Shale is older than basalt intrusion 2 Shale is older than sandstone 3 An unconformity exists directly under the shale.

12 Sediments and cracks Sediments have been weathered, eroded and deposited before they became part of a larger rock. The sediments must be older than the rock. Cracks, joints and veins form after the rock

13 Inclusions If a sediment falls into lava, it may become included if it does not melt. The inclusion is older than the lava.

14 Correlation ( co-relation) Matching rocks in one area with rocks in another area helps determine history of events on Earth. –Comparison of rocks –walking the outcrop –Matching up layers of rock separated over time



17 Correlation Index fossils –Similar fossils that existed for a brief period of time but appear in layers of rock (strata) all over the world.




21 Matching up index fossils helps correlate layers of rock and age them.

22 Which layers are the same age? How old are they? (ESRT pg 8/9)

23 Correlation Volcanic Ash or Meteorite Debris –A thin layer of fine sediment spread over the Earth that settles and is trapped between layers of rock

24 Volcanic Ash layer

25 Layer of Meteorite Debris


27 Unconformities – something is missing Layers of exposed rock get eroded and leave gaps in the geologic record Four steps to unconformity: –Uplift –Erosion –Subsidence (submergence) –Deposition

28 Four steps to unconformity

29 Missing info in the rock layer

30 Types of unconformities Angular – tilted or folded layers that have been eroded and recovered Parallel – also called disconformities, parallel layers separated by an erosional surface Nonconformities – sedimentary layers deposited on top of eroded igneous layers


32 Grand Canyon Geology

33 HW: Youtube review Relative Dating of the Earth O7woJ3I&feature=related O7woJ3I&feature=related

34 What is the correct order of development from oldest to youngest? Do Now:

35 Bedrock outcrops A and B are located at two different locations along the Genesee River in western New York State. Rock layers 1, 2, and 4 are the same in both outcrops. Which statement best explains why rock layer 3 is missing from outcrop B? (1) A fault exists between outcrops A and B. (2) Erosion created an unconformity between rock layers 2 and 4 in outcrop B. (3) A volcanic eruption destroyed rock layer 3 in outcrop B. (4) Metamorphism of outcrop A created rock layer 3.

36 Earth’s Geological History


38 Arrange the order of the following time measurements from biggest to smallest: Year Second Epoch Era Minute Hour Month Eon Period Century Decade Day

39 ESRT: page 8/9 How old is the Earth? 2 eons….which one are we in now? Identify the era, period and epoch we are currently living in. How many eras ago did our current epoch begin?

40 Eurypterus… a NY State Index Fossil Find me on the ESRT pg 8-9.

41 Using index fossils on the ESRT What period did Eurypterus live? What era? What eon? How many years ago? What was happening with life on earth? What was happening in NY State?

42 Index fossils – Page 8-9 ESRT Index fossils – any animal or plant that is characteristic of a particular span of geologic time or environment. 2 criteria to be an index fossil: Life form lived over a wide geographic area – horizontal distribution Life form existed for a short period of time – short vertical distribution

43 Location A Location B Location C Rock layer 1 WWW Z Rock layer 2 W Z Y Z Rock layer 3 W X X X Z Which letter would make a good index fossil?

44 Which graph shows the relative duration of geologic time for the Precambrian, Paleozoic, Mesozoic, and Cenozoic time intervals?

45 What is the geologic age of layer B? (1) Cambrian (3) Devonian (2) Ordovician (4) Permian

46 Evolution of life of Earth

47 HW: Youtube review Age and events of the earth – pg. 8 ature=related ature=related Index fossils – pg. 9 ure=related ure=related Linking pgs. 2,3,8,9 ature=related ature=related

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