�Unit 5: Earth History�OBJECTIVE: TO DETERMINE THE RELATIVE AGES OF ROCK LAYERS, INTRUSIONS, EXTRUSIONS, FOLDS, FAULTS, AND UNCONFORMITIES�

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Earth’s History

• “The present is the key to the past”

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Fundamental Principles

Uniformitarianism

• Geologists infer that the processes they observe today are similar to those in the past
• A.K.A: History repeats itself……!
• How was earth shaped?
• Earthquakes
• Volcanoes
• Plate tectonics
• Weathering, Erosion

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

1. Original Horizontality

• Sediments that are deposited in water are usually deposited in flat layers

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Geologic Time

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Flat, Sedimentary Layers

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

2. Law of Superposition

• This law states that the rock at the bottom of an “undisturbed” exposure are usually the oldest!
• There are some exceptions:
• Overturned Folding
• Reverse Faulting

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Superposition is well illustrated by the strata in the Grand Canyon

Sequence A forms during lower sea level

Sequence B forms during higher sea level

3. Cross-cutting relationships

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

3. Cross-cutting Relationship

• Fold, fault intrusions of magma are always younger than the rock they invade!

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Folds and Faults

• Folds: are bends (or tilted)in the rock layers produced by crustal plate movements
• Faults: are breaks in the rock where rock layers have shifted and are offset (don’t line up)

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Folding

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Tilted Layers

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Fold

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Fold

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

FAULT

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

��FOLD OR FAULT???��

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Write the letter of the Older layer

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Write the letter of the Older layer

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

6. Fossils

• Fossils: the preserved remains or traces of living things
• Hard parts of an animal (bone/teeth/shells)
• Amber
• La Brea Tar Pits
• Trace Fossils: impressions of shells, footprints
• Coral/Wooly Mammoth remains in NY
• Weather conditions

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Amber

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

La Brea Tar Pits

http://en.wikipedia.org/wiki/La_Brea_Tar_Pits

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

http://www.bbc.co.uk/sn/prehistoric_life/dinosaurs/making_fossils/

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

* A unit of rock is always older than the process that change it!

1) Extrusion: occurs when molten rock flows onto the earth’s surface

• Contact metamorphism on bottom layer only

2) Intrusion: occurs when magma squeezes into or between layers of pre-existing rock.

• Contact metamorphism on both layers

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

CONTACT METAMORPHISM�

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

CONTACT METAMORPHISM�

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Unconformities

• An unconformity is a buried erosional surface.
• An unconformity represents missing rock layers.
• An unconformity represents a gap in geologic time

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Establishing a Geological Sequence

1. No single location shows a complete record!
2. Weathering and erosion will take place if strata is located above water!
3. Erosion causes gaps in the geological record!
4. A buried erosion surface is called an unconformity!

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Unconformities are formed when……�

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• Rock layers are deposited
• Uplifted and eroded
• Subsided (submerged under water )
• More layers are then deposited on top of the erosional surface

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Formation of an �angular unconformity

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

UNCONFORMITITES�There are three types

• DISCONFORMITY: occurs when horizontal rock layers are on top of other horizontal rock layers.
• NONCONFORMITY: occurs when sedimentary rock layers are on top of nonsedimentary rock layers.
• ANGULAR UNCONFORMITY: occurs when horizontal rock layers are on top of tiled rock layers.

http://www.wwnorton.com/college/geo/egeo2/content/animations/10_4.htm

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

The Great Unconformity of the Grand Canyon

Nonconformity

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Angular Unconformity

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Disconformity

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

DISCONFORMITY

The Great Unconformity's missing 1.2 billion years represents about 25% of the earth's history.

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

ANGULAR UNCONFORMITY

A Nonconformity

NONCONFORMITY

Several unconformities are �present in the Grand Canyon

An Angular Unconformity

The Steps in Forming an Unconformity

• uplift of rock layers above sealevel
• erosion of rock layers
• subsidence of rock layers below sealevel
• deposition of new rock layers

Practice: Try establishing a geologic sequence. Oldest to Youngest

G,F,E,I,D,X,Y,C,B,A,H,J

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Do Now – You have Seven minutes

Looking at the worksheet, determine which lettered feature in each is older.

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*Remember that intrusions are always younger than the rock they cut across! Also, use your notes on the laws of geology to help you!

Oldest rock layer

Youngest rock layer

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

What type of landscape feature is this?

Plateau

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Colorado Plateau

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

The diagram below represents various sedimentary rock layers and the geologic periods during which they formed. According to the Earth Science Reference Tables, between which rock layers does a geologic time gap exist?

A and B B and C

C and D D and E

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Radioactive Decay:�OBJECTIVE:

• To determine the absolute age, in years, of a rock or fossil using the radioactive decay method, including the isotope, decay product, and half life

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Location- Front Page of E.S.R.T.

5,700 yrs

1,300,000,000 yrs

4,500,000,000 yrs

49,000,000,000 yrs

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

What is Radioactive Dating?

• Occurs when a unstable atoms begins to break down.
• Isotopes are atoms that have extra neutrons.
• Isotopes are unstable.
• Unstable means the atom will break down over time.
• An isotope will break down into a different element called a decay product.

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Radioactivity and �radiometric dating

• Atomic structure reviewed
• Nucleus
• Protons – positively charged
• Neutrons
• Neutral charge
• Protons and electrons combined
• Orbiting the nucleus are electrons – negative electrical charges

Radioactivity and �radiometric dating

• Radioactivity
• Spontaneous breaking apart (decay) of atomic nuclei
• Radioactive decay
• Parent – an unstable isotope
• Daughter products – isotopes formed from the decay of a parent

What is Half-life…

• If the nucleus of an isotope has more or fewer than the number of neutrons in its stable form, the isotope may be radioactive.

Ex:

Carbon-12 vs. Carbon-14

C-14 is Radioactive!!!!!!!!

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Types of radioactive decay

Radioactive Decay of Rubidium to Strontium

Fig. 9.14

Half-life continued…

• Studies show that the half-life for any element is not affected by environmental conditions.
• Thus, leading to concrete absolute ages.

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So the big question……!!!!

How do scientists determine a date?

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

It’s quite simple!!!

• The decay-product ratio!
• After the ratio is determined, we can then calculate how many half-life’s the radioactive isotope when through.

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Ex) A sample contains equal amounts of carbon-14 and its decay product nitrogen-14. How many half-life’s has it gone through? How old is the sample?

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Selecting the Best Radioactive Element for a Sample

Video: Carbon-14

• We have to consider the sample’s estimated age.
• Carbon-14 can date samples no older than 50,000 yrs.
• Uranium-238 half-life is too long to accurately date anything on Earth, besides the Earth itself!!!

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Radioactivity and �radiometric dating

• Carbon-14 dating
• Half-life of only 5730 years
• Used to date very recent events
• Carbon-14 produced in upper atmosphere
• Incorporated into carbon dioxide
• Absorbed by living matter
• Useful tool for anthropologists, archeologists, historians, and geologists who study very recent Earth history

OTZI the ICEMAN: 5300 years old

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

• To summarize:
• You find out what % of un-decayed material remains
• Determine how many ½ lives it has gone through
• Multiply the number of ½ lives by the length of each ½ life. The answer is the age of the artifact.

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Radioactive Dating

• This allows the Geological Time Scale to become a ABSOLUTE time scale.
• Meaning: unit of time is being added!

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Half-life continued….

• The radioactive isotope will break down into a different element called a decay product.
• The decay of an radioactive element is measured by its half-life.
• At the end of one half-life. A sample contains equal amounts of radioactive element and its decay product.

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Each time ½ of what was left changes into the decay product, the sample has finished another ½ life. �

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

The radioactive decay curve

Let’s Practice!!!

Why is carbon-14 not usually used to accurately date objects more than 50,000 years old?

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1. Carbon-14 has a relatively long half-life and not enough carbon-14 has decayed after 50,000 years.

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B) Carbon-14 has been introduced as an impurity in most materials older than 50,000 years.

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C) Carbon-14 has a relatively short half-life and too little carbon-14 is left after 50,000 years.

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D) Carbon-14 has only existed on Earth during the last 50,000 years

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Which radioactive substance would probably be used in dating the recent remains of a plant found in sedimentary deposits?

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A) carbon-14

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B) potassium-40

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C) rubidium-87

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D) uranium-238

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Let’s Practice!!!

If the amount of carbon-14 in the original sample had been 48 grams, about how much carbon-14 would have been left after 17,100 years?

A) 12 grams

B) 6 grams

C) 3 grams

D) 24 grams

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A sample of rock contained 100 grams of potassium-40 (40K) when it was formed. Today the rock contains 50 grams of potassium-40 (40K). According to the Earth Science Reference Tables, what is the age of the rock?

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A) 1.3 x 10⁹ years

B) 5.6 x 10⁹ years

C) 2.8 x 10⁹ years

D) 4.5 x 10⁹ years

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

1. If the amount of a radioactive isotope decreases as it decays, its half-life

1) increases 2) decreases 3) remains the same

2. Why are radioactive materials useful for measuring geologic time?

1) the disintegration of radioactive materials occurs at a predictable rate

2) the half-lives of most radioactive materials are less than 5 minutes

3) the ratio of decay products to undecayed materials remains constant in

sedimentary rocks

4) measurable samples of radioactive materials are easily collected from most

rock types

3. The age of the Earth is most accurately estimated from

1) the salinity of the oceans

2) the thickness of sedimentary rocks

3) studies of fossils

4) radioactive dating of rock masses

4. An atom that possesses a different number of neutrons than the normal form of the

element is called

1) an isotope 2) a chemical 3) an ion 4)an electron

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Radioactive Decay

Directions: Using the “Radioactive Decay Data” chart on the front page of your E.S.R.T, answer the following questions.

1. If the amount of carbon-14 in the original sample had been 48 grams, about how much carbon-14 would have been left after 17,100 years?

A) 12 grams B) 6 grams

C) 3 grams D) 24 grams

2. A rock contains uranium-238, which has a half-life of 4.5 x 10⁹ years. If the rock is crushed and heated, the half-life of the uranium-238 it contains will

A) Increase B) remain the same C) decrease

3. A sample of wood was found in an ancient tomb contains 25 percent of its original carbon-14. What is the approximate age of this wood?

A) 2800 years B) 5700 years

C) 11,400 years D) 17,100 years

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

4. If a sample contains 25g of Carbon¹⁴ and 175g of Nitrogen¹⁴, how many half-lives has it undergone?

5. How old is a bone in which the Carbon¹⁴ in it has .undergone 3 half-lives?

6. What happens to the amount of Nitrogen¹⁴ as the Carbon decays?

RADIOACTIVE DECAY� DIRECTIONS �GROUPS OF 3�

• MATERIALS:
• 1 ORANGE SHEET
• 1 YELLOW SHEET
• 2 COLORED PENCILS
• LAB SHEET (CHART AND GRAPH)
• RED CUP

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Report sheet changes

Trial No. No. Objects before shaking

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Decay Product

0

Number of %

objects “decayed” decay

ISOTOPE (Parent)

Half-Life (0) _________??

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

DIRECTIONS

• Pour mini M&M’s onto Isotope Sheet, count. Record as Trail 0, Isotope # above chart. (Record 0 for decay product)
• See me if you do not have an EVEN number.
• Flip ½ of the M&M’s over (“m” facing down and move them to Decay Product Sheet. This represents 1 Half-Life. Count the number of Isotope and decay Product. Record #’s on chart half-life (Trial) 1.
• Repeat for each trial until the isotope has decayed completely(is gone).

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Correlation Objective

• To match layers of rock strata that are located far apart, using the methods of…
• Walking the outcrop
• Similar rock types/sequences
• Volcanic ash layers
• Index fossils

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Correlating Rocks

• How do we correlate rocks?

(Match the rock strata in one location with the strata in a more distant locating).

• Walk the outcrop: write down what characteristics you see in the rocks/layers
• Compare rock type, thickness, color, fossils and the sequence of layers
• Does the same rock type mean the same age?
• Volcanic Ash: deposited rapidly over a large area

Practice: http://regentsprep.org/Regents/earthsci/rockcorrelation.htm

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Using Fossils to Correlate Rocks

• Index fossil: are the remains of organisms that existed for a relatively brief geological time but found over a wide area.
• Humans (Neanderthal)

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Natural casts of shelled invertebrates

Fossils: evidence of past life

• Types of fossils
• Indirect evidence includes
• Tracks
• Burrows
• Coprolites – fossil dung and stomach contents
• Gastroliths – stomach stones used to grind food by some extinct reptiles

A dinosaur footprint

Fossils: evidence of past life

• Conditions favoring preservation
• Rapid burial
• Possession of hard parts
• Fossils and correlation
• Principle of fossil succession
• Fossils succeed one another in a definite and determinable order
• Proposed by William Smith – late 1700s and early 1800s

Determining the ages of �rocks using fossils

Fossils: evidence of past life

• Fossils and correlation
• Index fossils
• Widespread geographically
• Existed for a short range of geologic time

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Earth’s History Objective

• Explain how geologic history has been divided into different ages, using the ESRT list life forms and extinctions, plate movements, mountain building events that occurred during earth’s geologic past

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Geologic time scale

• Subdivisions
• Eon
• Four eons
• Archean
• Hadean – the oldest eon
• Era
• Subdivision of an eon

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Geologic time scale

• Subdivisions
• Era
• Eras of the Phanerozoic eon
• Cenozoic ("recent life")
• Mesozoic ("middle life")
• Paleozoic ("ancient life")
• Eras are subdivided into periods
• Periods are subdivided into epochs

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

The Geologic Time Scale

PRECAMBRIAN EON�4.6 BYA-542 MYA

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

EON

Earth and Solar System forms�4.6 billion years ago (BYA)

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

OUTGASSING

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

World’s oldest rock 4.4 byo

Stromatolites (ancient algal reefs)�Oldest micro fossils 3.3 bya

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Cyanobacteria photosynthesis converts atmosphere from CO2 to oxygen 3.3 to 2.2 bya

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Oxygen atmosphere 2.2 bya

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Sexual reproduction 1.2 bya

Not a good idea to show a picture of sexual reproduction, is it?

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…evolution allows for beginning of diversity and start of Phanerozoic EON

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Paleozoic Era Age of Ocean Life�542-251 mya

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

MAJOR EXTINCTION (251 MYA)�95 % of life on earth died out�Diameter 6-7 miles

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Impact craters

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Mesozoic Era 251 -65.5 mya�Age of Dinosaurs

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Mass Extinction, including dinosaurs 65.5 mya est DIAMETER 1-4 miles�

YUCATAN PENINSULA MEXICO

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Cenozoic Era 65.5-0 (today) mya�Age of Mammals�

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Meteor Crater 50,000yrs ago�150 foot diameter

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Russian Meteorite Feb 15, 2013�55 foot diameter

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Geologic time scale

• Difficulties in dating the time scale
• Not all rocks have fossils
• Not all fossils have been discovered
• Some fossils have been destroyed
• Not all rocks are datable (sedimentary ages are rarely reliable)
• Materials are often used to bracket events and arrive at ages

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Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Do Now – 5 Minutes

According to the Earth Science Reference Tables, which rock is most likely the oldest? Hint: use “Life on Earth” column!!!

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A) conglomerate containing the tusk of a mastodon

B) sandstone containing fossils of flowering plants

C) shale containing trilobite

fossils

D) siltstone containing dinosaur footprints

An unconformity between two sedimentary layers is most likely produced by:

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A) uplift followed by extensive erosion, submergence, and deposition

B) a period of extrusive volcanism followed by another period of extrusive volcanism

C) continuous sedimentation in a deep basin over a long period

D) the deposition of gravel followed by the deposition of sand and silt

Answer - C

Answer - A

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections

Objective: To determine the relative ages of rock layers, intrusions, extrusions, folds, faults, unconformities in geologic cross sections