Regents Earth Science –Unit 12: Geologic History

Regents Earth Science ¨C Unit 12: Geologic History

Earth¡¯s History

Fossil - the remains or evidence of a living thing

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only hard parts fossilize

found in sedimentary rock

Official NYS fossil: Eurypterid

Types of Fossils

Fossils can form in the following ways:

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Petrification ¨C replacing living tissue with minerals

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Preserved Fossils ¨C frozen or amber

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Casts and Molds ¨C imprints of tracks, etc.

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Drying ¨C mummies

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Others

Fossils

Fossil Formation:

1.

Organism dies

2.

soft parts decay or are eaten

3.

hard parts are buried in sediment

4.

sediment becomes rock

5.

uplift, weathering and erosion

expose the fossil

Fossils

Fossils Indicate Four Factors in Earth¡¯s History:

1.

life changed/evolved over time

2.

Earth's surface has changed

? marine fossils are found at high elevation

3.

Earth's climate has changed

? tropical coral fossils are found today in NYS

4.

appearance and activity of past life

? teeth give clues to what an animal ate

? bones give clues to how the animal looked and move

Earth¡¯s History

Two Processes help us determine the age of earth¡¯s rocks and events:

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Relative Dating ¨C determining if something is older or

younger

Absolute Dating (Radioactive Dating) ¨C determining an

approximate age in years

Relative Dating

Relative Age - the age of something compared to something else

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Geologic Column - an ideal sequence of rock layers created

by combining data from all known rock sequences at various

locations

Relative Dating

youngest

Rules of Relative Dating:

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Law of Uniformitarianism - processes that change Earth today are the same as those

that changed it in the past

? "The Present is the Key to the Past"

Principle of Original Horizontality - sedimentary rocks form in horizontal layers

(sedimentary rocks not in horizontal layers have been changed since they formed)

Principle of Superposition - in any undisturbed sequence of rocks, the oldest rocks are

at the bottom, youngest at the top

Rocks are older than the events that happen to them (because the rocks exist first)

oldest

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Tilting, Folding, Faulting, and Intrusions are all younger than the rocks they effect

Tilting

Folding

Unconformity - buried erosional surface, represents a gap in time in Earth's history

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Formation of an

Unconformity:

Faulting

Intrusion

Relative Dating ¨C Sequence of Events

Sequence of Events ¨C putting events in order of age from what

happened first to what happened last

Sequence of Events:

1.

deposition of limestone

2.

deposition of sandstone

3.

deposition of shale

4.

deposition of limestone

5.

deposition of sandstone

6.

faulting of rock layers

7.

intrusion of igneous rock

Sequence of Events that formed the landscape cross-section at the left:

1.

2.

3.

4.

5.

6.

Deposition of layers 1-5

Intrusion of #6

Tilting of layers 1-5 and Intrusion of #6

Erosion of rocks

Deposition of layers 9,10

Erosion of rock layers

relagecy cle.gif (29947 by tes)

Relative Dating - Correlation

Correlation ¨C matching rock layers from around the world

Index Fossil - a fossil of an organism that lived for a short,

well defined period of time and lived over a large

geographic area

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used to date the rock layers in which it is found

index fossil

Index Fossils:

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