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