Interpreting Geological History Aim GeoHis 1a - How old is Mr. Foley relative to the planet Earth?

Interpreting Geological History

Aim GeoHis 1a

- How old is Mr. Foley relative to the planet Earth?

Reading the Rock Record

Human recorded history only 10,000 years of recorded human historySince the Agricultural Revolution 8,000 BCE

Geologic history 4.6 billion years old

Cosmological HistoryOur universe is 13.8

billion years old

Relative Dating

This is not talking about how old your Aunt Matilda’s is!

Relative dating - the age of one object, rock, fossil, event compared to another

Example: Who is oldest:Mr. Foley?The Earth?Mr. Foley’s daughter Katie?

Another Example of Relative Dating – place the following in number order

1. Japanese Attack on Pearl Harbor

2. Abraham Lincoln’s Gettysburg Address

3. Atomic bombing of Hiroshima

4. The September 11 attacks

5. Columbus discovers America

6. First men land on the Moon

7. John F. Kennedy is assassinated

8. Signing of the Declaration of Independence

9. The Titanic sinks after hitting an iceberg

An Example of Relative Dating

5. Columbus discovers America

8. Signing of the Declaration of Independence

2. Abraham Lincoln’s Gettysburg Address

9. The Titanic sinks after hitting an iceberg

1. Japanese Attack on Pearl Harbor

3. Atomic bombing of Hiroshima

7. John F. Kennedy is assassinated

6. First men land on the Moon

4. The September 11 attacks

Absolute Time

Identifies the actual date of an eventExample - the date that Pearl Harbor

was bombed would be absolute If two dates are known for two events than the length of time between the

events will be knownWe can calculate rates of change

how long a mountain took to build uphow many years it took for a glacier to

advance

Absolute Dating with Radioactive Elements

The Earth, from its origin, has had radioactive elements within it

Radioactivity – the breakdown of unstable atoms due to too many or too few neutrons in the nucleus

Energy is released when radioactive elements breakdown or decay

This heats the Earth’s interior

Absolute Dating with Radioactive Elements – three types of decayThere are three types of decay

Alpha decay - a helium particle is emitted

Beta decay - a high energy electron is emitted

Gamma decay – a high energy electromagnetic wave is released

Half Life A time period equal to how long it

takes half of a radioactive sample to decay

Typical Half Life graph

Correlation – How layers of rock relate to each other

Allows us to SEQUENCE events Shows relative as well as absolute dating

Allows us to FINDUseful minerals Fossil fuels like coal and oil

Correlation is done byStudying exposed bedrock (outcrops)Looking for similarities between two

different places Following the Laws of Rock Sequencing

1st Law - Law of Superposition

If sedimentary rock layers are undisturbedLowest layers of sedimentary rock will be the

oldest

2nd Law - Law of Cross-Cutting Relationships

If an intrusion of igneous rock cuts across existing sedimentary rock

It is younger than the sedimentary rock

3rd Law - Law of Included Fragments

Pieces of rock found in another rock must be older than the rock they were found in

Each mineral is older than the rock it makes up!

Example A conglomerate rock Contains granite,

limestone,

and clay Rock is younger than the three

materials in the rock

4th Law - Law of Unconformity

A place where rock layers are missingEither rock layers are lost due to erosion

or may not have been laid down at all Creates gaps in

the rock record

(“Darwin’s Bane”)

Unconformities are erosional features…

might we lose a fossil or two?

Correlations Continued

Aim GeoHis 2 - How do I use the Laws of Geology to figure out the age of rock layers or strata?

Some examples of Correlations

In the following diagram at the right

Give the order of the layers produced

From oldest to youngest1. M2. L3. Lava Flow A4. Magma Chamber N5. K, J, H, G, F6. Intrusion I7. Sill E8. D9. Lava Flow B10. C

C

L

M

N

H

FE

D

I JK

G




From oldest to youngest1. A2. B3. C4. D5. Fault line G6. Unconformity7. E8. F9. Intrusion H10. Contact Metamorphism of F

E

C

B

F

D

A

Intrusion H Fault line G




From oldest to youngest1. A2. B3. C4. D5. Fault line G6. Unconformity7. E8. F9. Intrusion H10. Contact Metamorphism of E and F

C

B

D

A

Fault line G

F

E

Mountains and Plate Tectonics Revisited

Active and Passive Continental Margins - the edges of continents

1. Active marginsoccur along the edge of a plate boundaryproduce earthquakes and volcanic activitymountain building results Ex: Andes Mtns of South America (“Alive”)

What Characteristics Occur in Collision Mountains

Faults – where plates meet

Types of faults strike-slip faults

shear forces - sideways

normal faults tensional forces – pull apart

thrust faults compression forces – push together

all build up mountains by pushing crustal materials up into piles

What Characteristics Occur in Collision Mountains

Folds – when plates collide – sometimes earth folds upAnticlines

upfolds of rockSynclines

downfolds of rockA fjord in Norway

Other Evidence of Mountain Building

Uplifting – proof of increasing elevations:fossils

marine animals found at higher elevation

raised beachesexample CaliforniaShows measured changes in elevation

along coastlines

Holy Schist! That’s a big fossil clam!


Tilting areas where large amounts

of sedimentary rock are tilted due to movement of the crust

Ex: Rocky Mtns in Colorado sedimentary rocks

Fault block mountains Areas where numerous fault

lines occur May create a series of

raised mountain segments

Horst – the raised part of the fault block

Graben – the lowered part of the fault block


Overturning When sedimentary

layers are flipped over Can occur due to

excessive tilting What is the Law of

Superposition and how does this break that law? Oldest rocks on bottom,

youngest on top In overturning, its

reversed!

Sed Rock Layer 1 myo










Fossils and the Age of Rock

Aim GeoHis 3c – How do fossils help us date rock strata?

The Fossil Record

Fossils – any evidence of earlier life preserved in a rock

Found only in

sedimentary rock…Why???

Fossils - Original Remains

Parts of the actual animal or plantPreserved in ice, tree sap, or peat

(from bogs)Examples

Wooly Mammoths – frozen in ice Insects, seeds, plant parts – stuck in amber

(tree sap will harden)The Bog People – buried in a bog (swamp)

Examples of Original Remains

Dinosaur bones

The calcium in the bones is replaced by other minerals

Over time, the bones last longer

An example of Archaeopteryxan ancient ancestorto modern birds

Fossils - Replaced Remains

Soft parts lost thru decayHard parts replaced by other minerals

such as:CalciteSilicaPyrite

Hardens to form a mineral-like substanceExamples – petrified wood!

Examples of petrified wood

Fossils - Molds and Casts

A plant or animal falls into some sediments (ex: mud or clay)

Plant or animal decays, but leaves outline in sediment (a mold)

Sediments then form sedimentary rockIf other materials fill in the moldA cast is formed

Examples of Molds and Casts

Shells Molds

Trace Fossils

Evidence of life other than actual remainsExamples:

FootprintsTracksTrailsBurrowsBoringsCoprolites…

Foot prints

Tracks

What happened here??? Someone was having dinner, and someone WAS dinner!

Coprolites

What is it? Oh no! Dino Poo!!! Tells us about the things they ate…

Index Fossils and Key Beds

Index fossils Excellent for RELATIVE dating Fossils with three special

characteristics:1. Easily recognized

2. Widespread throughout the world or a region

3. Occurred in very specific time periods

Index Fossils and Key Beds

Key Beds – rock layers that have the same characteristics as an index fossil

This can be done across the face of the Earth Best example – iridium layer at 65 mya

(who died?)

Geologic Timetable Geologic timetable – see ESRTs pp. 8-9 A summary of the major events in geologic history

– includes: Time scales What life was on earth during those time scales The NYS rock record – what time scales we have

evidence of What animals and plants were found in NYS and what

time periods their fossils came from Major North American and NY tectonic events The position of North American relative to Pangea

Geologic Timetable

Era - the longest segment of geologic time Each era broken into periods Each period broken into epochs

Archean Era Began 4.6 billion years Oldest rocks come from this time range

Proterozoic Era Began 2.5 billion years ago First fossils of simple plants and worms found here

(oceans only)

Geologic Timetable

Paleozoic EraBegan 570 million years agoAbundant fossil recordLand and ocean animals and plants

The Paleozoic – Life takes on a whole new meaning

Geologic Timetable

Mesozoic EraBegan 250 million years agoRise and Fall of the DinosaursEarliest birds and mammalsRise of flowering plants over

conifers

Mesozoic Era – Rise of the Dinosaurs

What really killed off the dinosaurs…

Geologic Timetable

Cenozoic Era Began 65 million years ago Rise of the birds and mammals Ice ages Mammoths and Saber tooth tigers Human Epochs

Australopithecus afarensis – “Lucy” of Olduvi Gorge Homo habilis – “handy man” Homo neanderthalsis – the “caveman” Homo sapiens – “thinking man” Homo sapiens sapiens – modern man

Cenozoic Era

Half Life Calculations

Aim Geo His 5e – How does radioactivity allow us to date the dinosaurs?

Half Life

The time it takes for a naturally occurring

radioisotope to decay half of its

amount

Half life is constant - cannot be altered by:

Temperature

Pressure

Chemical changes

See Page 1 of ESRTs Radioactive Decay Data

Half Life Calculations• The age of a fossil or rock strata (layer) • can be determined from the fraction of original

radioisotope is left over• Example:

• You have a mammoth with only ¼ the amount of carbon-14 (a radioactive substance) left in it. How long has the mammoth been there?

• If you started with 1 gram of C-14• After one half life of time you would have ½• After two half lives, you would have ¼• Carbon-14’s half life is 5,700 years• So 2 half lives x 5,700 years = 11,400 years

Half life example 2: A sample rock has only 15.0 grams left of the original 200 grams of radioactive material. How many half lives went by?

• 200 grams x ½ = 100 grams• 100 grams x ½ = 50 grams• 50 grams x ½ = 25 grams• Three half lives went byHalf life example 3: A sample has only 10 grams left after 4,000 years have gone by. If one half life of the radioactive material is 1,000 years long, how much radioactive material was started with?

• 4,000 years total divided by 1,000 years = 4 half lives• 10 x 2 = 20 • 20 x 2 = 40• 40 x 2 = 80• 80 x 2 = 160 grams of original material

Example 4: A chunk of Co-60

appears at the right. If the

shaded area is radioactive,

how many half lives occurred?

Fraction remaining = ¼ = ( ½ ) t/T

t/T = number of half lives

= 2

Half life

Radioisotopes

Aim – Nuke 6 – What are they used for?

Uses of Radioisotopes

Radioactive Dating

By comparing the ratio of parent radioisotopes to daughter nuclei

Age of various materials can be determined

Examples• C-14 vs C-12

–archeological evidence• U-238 vs Pb-206

–rock formations–Much longer half - lives

Dating “Stuff” If we know how much of the radioactive element there is left, we can determine the age

Ex: If we started with 400 grams of Ra-226, and now we only have 50 grams, how many half-lives passed?

Fraction remaining = 50 / 400 = ( ½ ) t/T

1/8 = ( ½ ) t/T

number of half lives = t/T = 3How much time has passed (hint – what is the half life of Ra-226)?total time passed = 1600 y x 3 half lives

= 4800 y

Half life – the time it takes half of a radioactive isotope to decay or breakdown

Example: Carbon-14 has a half life of 5,700 years: Start with 100 grams of C-14

How much is left after 5700 yrs? _____________ How many half-lives have passed? ___________

How much is left after 11,400 yrs? ______________ How many half-lives have passed? _____________

How much is left after 4 half-lives? _____________ How many years have passed? ______________

Dating “Stuff” If we know how much of the radioactive element there

is left, we can determine the age Ex: If we started with 400 grams of Th-234, and

now we only have 50 grams, how many half-lives passed?

How many days have passed?

For dinosaurs, rocks, and prehistoric items U-238 is used – half life of 4.6 billion years

For man made or historical items Carbon-14 is used (Ex: Shroud of Turin)

Half Life Lab Name __________________

IntroductionHalf life – involves both an amount of material and a time

period the amount of material is the remaining radioisotopes the time is the time it takes half the radioisotopes to

decay

Objective To collect half life data To create a half life graph To explain how half life can be used to determine the

age of objects or rock layers

Half Life Lab

VocabularyRadioisotope -

Decay -

Radioactive dating -

Parent isotope -

Daughter isotope –

Half Life Lab

Materials (per person) Ruler Full piece of radioactive linguine pasta

Procedure1. Measure the length of your piece of linguine2. Record this information in the Data Table3. Break the linguine in half (do not measure the half way

mark!)4. Throw one half away. Measure the length of the other

half. Record this info in the Data Table5. Repeat until you can not break the linguine in half

anymore

Half Life Lab – Data Table

Number of Breaks(Half-lives)

Length of Radioactive Pasta (cm)

% of original pasta remaining*

0 1 2 3 4 5 6 7 8 9 10 11

*The percent of original pasta is equal to

length at # = % of original radioactive pasta remaininglength at 0

100

90

80

70

60

50

40

30

20

10

0

Half Life Lab – graph % remaining vs half-lives%

of r

adio

act

ive

pas

ta r

em

ain

ing

0 1 2 3 4 5 6 7 8

Number of Half - lives

Half-Life – Do Now

1. The half life of radioactive pasta rotini equals three years, how many years will pass in four half lives?

2. What percentage of radioactive pasta rotini remained after 3 half lives?

3. A 100 gram sample of radioactive Pholium-280 is allowed to sit on a shelf for 30 days. At the end of this time, only 12.5 grams of the Pholium-280 remains. How long is one half life?

Half-Life Lab - Analysis

1. Using your graph, what length of radioactive pasta is left after 3 ½ breaks (half lives)?

2. How much of your radioactive pasta is left after 20 breaks (half-lives)?

3. Explain your answer to number 2 above.

4. An 800 cm sample of radioactive pasta is decays until there is only ¼ left. How many half lives went by?

Half-Life Lab - Analysis

5. Mr. Foley leaves the radioactive pasta at home for several days. When he brings it back in, only 25 cm is left. How many half lives have passed for the pasta?

6. If one half life of radioactive pasta equals 1 million years, how many years did your pasta last?

7. How many years did it take your pasta to reach ¼ of its original amount?

8. You find a sample of radioactive pasta mixed in with the fossil of a mammoth! Only 1/8 of the original pasta sample remains! How old is your mammoth fossil?

Half-Life Lab – Discussion Questions

9. Describe half life in terms of time.

10. Describe half life in terms of the amount of material that decays.

11. Could you have continued to break the pasta in half forever? Compare this to radioactive decay.

12. On page 1 of the ESRT’s, there are four radioisotopes. Which one has:a) The longest half life?

b) What could you use it to date?

c) The shortest half life?

d) What could you use it to date?

Half life – Two Tragic Questions

A dinosaur bone was found by Mr. Foley! He claims it is over 65 million years old! You find only 1/32 of the original radioactive pasta with the bone. Is Foley rich or ridiculous? Why or why not?

Mr. Foley abuses his class with one too many vacation assignments.

They beat him to death with the February assignment, and bury him and his precious pasta (half-life = 1,000 years) in the back of the school.

Future students of the Foley High School of Science in Hauppauge find his fossil remains and only 1/16 of the pasta.

What year is it?

Interpreting Geological History Aim GeoHis 1a - How old is Mr. Foley relative to the planet Earth?

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