earth’s geologic history aim: how do we determine the chronology of earth’s events?
TRANSCRIPT
Earth’s Geologic History
Aim: How do we determine the chronology of earth’s
events?
Vocabulary
Uniformitarianism Relative Age Horizontality Superposition Chronology Intrusions Extrusions Inclusions
Correlation Unconformity Index fossils
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
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
How can the older layers end up on top? Faulting Folding Crustal Uplift
Intrusions
Magma forcing its way into cracks and solidifying into igneous rock
The surrounding rock is older than he intrusion.
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
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
Order of events:
Name them oldest to youngest:
1 Shale is older than basalt intrusion
2 Shale is older than sandstone
3 An unconformity exists directly under the shale.
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
Inclusions If a sediment falls into lava, it may
become included if it does not melt. The inclusion is older than the lava.
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
Correlation
Index fossils– Similar fossils that existed for a brief period of time
but appear in layers of rock (strata) all over the world .
Matching up index fossils helps correlate layers of rock and age them.
Which layers are the same age?How old are they? (ESRT pg 8/9)
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
Volcanic Ash layer
Layer of Meteorite Debris
VOLCANIC ASH LAYER AT THE SAME TIME AS THE DINOSAURS BECAME EXTINCT LEAD SCIENTISTS TO LOOK FOR METEORITE CRATER Chicxulub Crater 65 mya 170 km. Wide
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
Four steps to unconformity
Missing info in the rock layer
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
Grand Canyon Geology
HW: Youtube review
Relative Dating of the Earth http://www.youtube.com/watch?v=gFtd
O7woJ3I&feature=related
What is the correct order of development from oldest to youngest?
Do Now:
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.
Earth’s Geological History
Arrange the order of the following time measurements from biggest to smallest: Year Second Epoch Era Minute Hour Month Eon Period Century Decade Day
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?
Eurypterus… a NY State Index Fossil
Find me on the ESRT pg 8-9.
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?
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
Location A
Location B
Location C
Rock layer 1
W W W Z
Rock layer 2
W Z
Y Z
Rock layer 3
W X X X Z
Which letter would make a good index fossil?
Which graph shows the relative duration of geologic time for the Precambrian, Paleozoic, Mesozoic, and Cenozoic time intervals?
What is the geologic age of layer B?(1) Cambrian (3)
Devonian(2) Ordovician (4)
Permian
Evolution of life of Earth
http://www.johnkyrk.com/evolution.html
HW: Youtube review
Age and events of the earth – pg. 8http://www.youtube.com/watch?v=dmUpOYvxiZw&feature=related
Index fossils – pg. 9http://www.youtube.com/watch?v=5fbx4TBIZPE&feature=related
Linking pgs. 2,3,8,9http://www.youtube.com/watch?v=dmUpOYvxiZw&feature=related