Geologic History Powerpoint Notes

Interpreting Geologic

History

If the history of our planet was condensed to only

one year, when would the “important” events in our history have taken place?

Reminder add about early earth formation

January to MarchOne quarter (1/4) of the year was over, and no life was present. The environment was extremely chaotic.Barren mountains dominated until the oceans formed in late March.

http://slafee.files.wordpress.com/2009/04/anza-borrego-desert.jpg

April to NovemberApril Fool’s Day = first life on Earth! Only single-cell organisms near thermal vents and in warm oceans.

Multi-cell organisms sprout up towards the end of August!

These types of life dominate all the way until December!

December

December 2nd – the first hard shelled organisms (trilobites).

December 3rd – more complicated sea-creatures begin to show up.

December 6th

60% of North America is covered by water!

STILL NO LIFE ON LAND!Endless torrential rain and huge amount of erosion over continents.

December 7th FINALLY, plants are able to make their way onto land.

Many are washed away by the torrential rain, but some are able to grab hold and latch on.

December 10th

Where are all the people??? Still nowhere to be found!

Fish are thriving in the oceans.Some grow feet, walk onto land, and call themselves Amphibians.

First land-only animals are on their way.

December 17th

Look out for the insects!At the end of the month, Jurassic Park opens up. Dinosaurs begin their reign on land.

December 20thThe Appalachian Mountains stand

taller than any other mountain chain on the continent! They later shrunk in their old age.

Dinosaurs are chasing the first mammals around, enjoying snack-time.

It’s snack time!!!

AHHH!!!

December 24th

An asteroid the size of Manhattan slams into the Yucatan Peninsula. The dinosaurs’ “one week” of dominance ends. The mammals are more than excited to see them go.

At the end of the day, the Rocky Mountains start to form.

December 25th

Here’s where the action kicks up!

Mammals are running around without having to worry about their buddy T-Rex.

The Mammal Baby-Boom begins.

December 28th

The Colorado River begins to cut through the land below it. A few days later, the Grand Canyon is about a mile deep.

December 31st Where are all of the humans? During

the morning and afternoon, there is still no sign of them.

At around 10 PM, early human ancestors appear.

Between 10 and 11 PM, massive ice sheets will advance and retreat over North America and Eurasia FOUR times.

The Last Hour on December 31st Neanderthals show up to the New

Year’s party.With a half hour left before the end

of the year, cavemen make drawings on the walls.

With fifteen minutes left, homo sapiens make the first weapons – spears and knives.

Civilizations appear in the last five minutes: Egyptians, Greeks and Romans each spend one minute building and destroying their empires.

The Last Minute of the Year!

With 3 seconds left in the countdown, Columbus stumbles into the Americas.

The Last Minute of the Year!

The Industrial Revolution began just one second before the New Year.

The Last Second of the Year!

Within the last 5 tenths (0.5) of a second, humans invented cars, planes, computers, TV, cell phones, and nuclear weapons.

Who’s Younger?How Do You Know??

“in a Nutshell”

Origins of our Solar System

Earth formed through the gravitational attraction and accumulation of asteroids and rocky debris

This accretion of material generated a tremendous heat causing the planet to be molten

The denser materials settled into the interior and the Earth’s layered internal structure formed.

Earth's first atmosphere 4.6 billion years ago was most likely comprised of hydrogen and helium (two most abundant gases found in the universe!) Through the process of outgassing, the outpouring of gases from the earth's interior, many other gases were injected into the atmosphere. These include: water vapor (produced rain - rivers, lakes, oceans) carbon dioxidenitrogenAs outgassing occurred over a period of millions of years, the atmosphere evolved to its current state

Life and Evolution

Diverse Ordovician Sea-Life

Evidence from the fossil record (preserved in sedimentary rocks) shows that a wide variety of life forms have lived in Earth’s changing environments over time.

The comparisons of fossil remains and current life forms enable scientists to make predictions about the Earth’s past environment.

A major reason for changes in Earth’s environment over geologic time has been the movements of plates and their associated landmasses.

The theory of organic evolution states that life forms change through time.

As environmental conditions change, variations within a species give certain individuals a greater chance for surviving and reproducing.

These variations, along with others get passed on to future generation leading to the creation of a new species.

The fossil record provides evidence for the theory of organic evolution.

This also shows that evolution does not always occur at the same rate.

There are times of rapid extinctions and subsequently rapid evolution of new species.

An impact event, such as the collision of a comet or asteroid with Earth, may cause catastrophic environmental changes leading to rapid extinctions and evolutions.

Such an event probable occurred at 65 m.y. and is associated with a massive extinction of roughly 70% of the Earth’s species.

Precambrian (4.6 b.y - 544 m.y.)Simple organisms (invertebrates)“Soft-Bodied” Organisms (Fossils are rare)

StromatolitesFormed from the trapping of sediment in layers by Blue-Green Algae (Cyanobacteria)

Paleozoic (544 – 251 m.y.a.)Organisms proliferate and become more complex (vertebrates)

Shelled (mineralized skeletons and shells) organisms develop

(Brachiopods/Trilobites)Amphibians develop from lobe-finned fish

Era ends with a mass extinction killing off more than 95% of the life on earth

Eurypterid (Sea Scorpion) Fossil

Largest fossil with human for scale

Eurypterid in Action

Phacops Trilobite of the Devonian

Carboniferous Forests – formed extensive coal deposits

Evolution of Amphibian from Lobe-Finned Fish (Devonian)

Mesozoic Life (245-65 m.y.a.)“Age of Reptiles” (dinosaurs, flying reptiles and birds develop)

Modern animals and plants begins to develop on land

Era ends with a mass extinction killing off dinosaurs, ammonoids, flying reptiles, and some swimming reptiles.

Triassic Plateosaurs

Iguanodons

Cretaceous T-Rex

Cenozoic Life (65 m.y.a. – present)“Age of Mammals” (mammals begin to develop and evolve)

Humans develop from primates (Homo Habilus 1.6 m.y.)

Early Hominids

Mastodonts

Scientists have determined the age of the Earth to be about 4.6 billion years old.

4,600, 000, 000 years = 4.6 x 109 years (scientific notations you should know)

109 = billion106 = million103 = thousand1012 = trillion

For example, 109 can be read as “one with 9 zeroes after it” OROR1,000,000,000

• Began in the late 1700’s when James Hutton published his Theory of the Earth.

• In this work he was the first scientist to argue effectively that geologic processes proceed over long spans of time

The physical, chemical, and biological processes that operate today have also operated in the geologic past.

“The present is the key to the past”

THE PRINCIPLE OF UNIFORMITY:

Geologists can infer events of the past by

Looking at features of rocks androck outcrops

Uniformitarianis

m(Principle of states that the forces that acted upon the

___________ crust…

Uniformity)

Earth’s

in the __________ are the same as those that are ____________

today.

pastactive

**THE KEY TO THE PASTIS THE PRESENT**

Relative Dating Techniques

Prior to the discovery of radioactivity, geologists had no reliable method of giving specific dates to geologic events and had to rely on relative dating techniques.

Relative Dating means placing rocks or events in their proper sequence of formation, based on a comparison to other rocks

5 Basic Laws: 1. Law of Original

Horizontality2. Law of Superposition

3. Law of Inclusions4. Law of Cross-Cutting

Relationships5. Law of Original Lateral

Continuity

Law of Original HorizontalityStrata is originally

deposited in flat horizontal layers because sedimentary particles settle from air and

water under the influence of gravity

Law of Original Horizontality

If strata are ___________, then they must have suffered some kind of disturbance after they were deposited.

Grand Canyon

Western Iran

Steeply Inclined

• Principle of Original Horizontality states that sediments are deposited in horizontal layers

Layer 1 – Siltstone

Layer 2 – Limestone

Layer 3 – Sandstone

THE LAW OF SUPERPOSITION:

the principle that the _________ layers in a sequence of rock

strata must have been deposited __________ the layers above,

unless the rock strata have been ___________ or___________

bottom

before

disturbeduplifted

The _______ rocks are found at the bottom.

Geologists can date the

_________ ages of the strata from

________ to __________

older

relative

oldestyoungest

oldest

youngest

Law of Superposition

Therefore the order of deposition is from the bottom upward.

Law of Superposition states that in an undeformed sequence of strata, each bed is older than the one above it and younger than the one below it.

Younger

Older

Oldest

Grand Canyon, Sequence of Strata

Oldest

Youngest

Which rock unit is the youngest? oldest?

Grand Canyon, Sequence of Strata

Older

Younger

Sheep Rock, Central OR

Law of Inclusions

A rock must first exist in order to be weathered, deposited and cemented as a _____ in another rock. Therefore…

clast

If rock is composed of _____________, the rock fragments must be ___________ than the rock in which they are found.

fragments

older

Law of Inclusions

Which is older the Granite or the Sandstone? In figure A? In figure B?

Sandstone is older

Granite is older

The law of inclusions also applies to fossils preserved in the bedrock.

_________ are any naturally preserved remains or impressions of living things.

Fossils

They are found in _______________ because

_____________________

____________

Sedimentary rock

Heat & pressure in igneous and metamorphic rock destroys them

FOSSILS GIVE US INFORMATION ABOUT

THE ANCIENT ENVIRONMENT AND CLIMATE

ESRT pp. 8-9

Spiral shellLower Cambrian to present dayFoot-like muscle used to move Environment:Land, Fresh Water, MarinePresent day example: a snailFed on algae

Worthenia

Varying shell shapes, not spiralLower Cambrian to present dayAttached themselves to rocksSymmetricalEnvironment: Benthic MarineFilter feeders

Mucospirifer

Of the Phylum ArthropodLower Cambrian to Late PermianMarine BenthicSome were believed to consume mud, filter feed or scavengePhacops

Squid-like creatures with shells. Swam with water propulsion. Predators had beaksChambers separated with suturesNautiloids lived from the Cambrian to present dayAmmonoids lived from the Triassic to the Cretaceous

Colonial or solitary animals, not plants!Captures small prey with stinging cellsLive in shallow marine water BenthicEx. Horn Coral (solitary)Lived from the Cambrian to present day

Lobster like creaturesLate Ordovician through

DevonianSea scorpions (Predators)Belong to the phylum

Arthropoda (the same as Trilobites)

Marine, land, and fresh water

Length could reach up to 2 meters long

Planktonic (floated around)Often good index fossils since they are found all over the world for a short period of time, in great numbers.Mid Cambrian Devonian Probably filter fed Once believed to be shark teeth

“Sea Lillies”Late Ordovician to present dayNormally the stems are foundBenthic Marine Filter feed

Not always symmetricalBurrowersMud Eaters BenthicMarine or Fresh waterOf the Phylum MolluskaCambrian to Present dayEx. Clams, mussels, scallops

Unconformity Buried erosional surfaces that are preserved in the rock record.Create “gaps” in the geologic rock record

Rock Fragments (or Inclusions) that are contained in another rock are older than the rocks in which they are found

Law of Cross-Cutting Relationships

Any __________ or ______, must be younger than all rocks through which it cuts. Simply put, the body of rock that is cross-cut had to be there first in order to be cut by an intruding igneous body or fault.

Igneous rock fault

In general rock is always_________ than the process that changed it.

older

Some Processes Include:

foldsfaultstiltsintrusionsextrusions

Intrusions are younger than the rocks that they intrude

• Faults (or cracks) are younger than the rocks that they cut through

• Extrusions are younger than the rocks they form above

Fault

Fold

Sedimentary layers(the law of original horizontality)

Sedimentary layers

The fault came after the rock was formed

Sedimentary layersThe tilt came after the the rock was formed

The extrusion came afterthe rock was formed

1

23

45Contact

metamorphism

1

23

45

6

The extrusion came after the lowerlayers were formed but….Before the top layer

1

234

5

This intrusion came after all the layers

1

23

45

6


1

234

5

This intrusion came afterall the layers

These changes can lead to exceptions to the Law of Superposition:

a.An __________ is an igneous rock that formed from lava on the surface of the crust.

extrusion

An __________ must be younger than the strata below it, but ________ than any layers above.

extrusion

older

1

23

45

6


b. __________ are created when molten rock (________) is injected into older rock layers in the crust.

intrusionsmagma

_____________ are_____________ thanall the rock layers in contact with them.

Intrusionsyounger

1

234

5

This intrusion came after all the layers

c. _______ are bends in the rock strata. ________ can overturn rock strata so that ________ rock lies on top of _________ rock.

Folds

folding

older

younger

d. _______ are cracksin rock strata. _______ produce offset layers.

Faults

Faults

Rock strata must be

________ than the process that changed it.

older

_________, ________ and ________ ___________

are features created after rock or sediment has been deposited.

cracks veinsnatural cement

The following diagram represents a cross-sectional view of a portion of Earth’s crust. What is the relative age of the igneous rock?

The igneous rock is older than the …

The igneous rock is younger than the …

Law of Original Lateral Continuity

. When sediment is dumped by an agent of erosion, strata extends from the source until it gradually thins to zero, or until it reaches the edges of the basin of __________. deposition

Folding of strata (rock layers) over upon itself

Strata is displaced by a Fault (Thrust Fault)


erosion

This concept enables us to correlate outcrops of strata that has been dissected by processes of ________.

Let’s follow the progression of geological events that formed the

sequence below.

Step One

Deposition of rock units A-E

Step Two

Area is uplifted, and is intruded by rock unit D (Sill)

Step Three

Intrusion of rock unit F (Dike)

Step Four

The rock sequence is tilted and then eroded, setting the stage for an angular unconformity

Step Five

Area subsides, followed by the deposition of rock units G-K

Step Six

Area is uplifted and the upper surface begins to undergo erosion

That is the story behind this rock sequence

CORRELATION OF ROCK STRATA:

Correlation is Matching similar rock strataat different locations to see if they formed at the same time

Correlation is the process of matching rock units or events in separate rock formations

Correlation of rock units and geologic events can be based upon continuity, similar rock composition, fossil evidence, and volcanic markers.

• Correlation by:• Continuity – “walking the outcrop”; performed by following a rock layer for great distances• Similarities in rock composition and texture can be used to match rocks over large areas

Grand Canyon Stratigraphy

Fossils can be used to help match separate rock layers

Unconformity

Correlation using Index Fossils

Ways to correlate rockformations:

“Walking the outcrop”

is done by Walking from end to end

This is correlation bycontinuity

You can match the rock strata in one location with rock

strata in more distant locations by Comparing

,

color texturecomposition

Time correlation compares ____________ contained in the

rock strataindex fossils

12

34

456

3

The best index fossils:

a. _________________

b. _________________

Exist for a brief period of time

are widespread

Which fossil would make the best index fossil?

Found in only 1 layer (short lived)Found in all samples (widespread)

Another way of correlating layers by time is through

___________________Volcanic ash falls

These ash falls are very ________ events. A single

layer of ______ can be found over a large area, this allows

geologists to make a__________________ from one location to another

at the position of a common ash fall.

briefash

time correlation

Volcanic Eruptions and Rock Correlation

Violent volcanic eruptions can emit large quantities of volcanic ash

The ash can spread out over a large area of land, creating an excellent geologic marker for rock correlation

GEOLOGIC TIME SCALE:

A. Geologists noticed that rock _________ can be identified by the fossils they contained.

formations

They also found that certain __________ were consistently located ________ or _________ other formations.

formations

abovebelow

From these observations they established a

______ ____ ______with a sequence of fossil groups from ______ to

______________

relative time scale

oldestyoungest

Each of these groups was named for a location where its ____________ ______ could be observed in the rocks.

Characteristic fossil

Example:Devon fossil “Devonian” found in Devon England

Further observations from around the world established a

________ _____ _____Geologic time scale

Based on __________________________________

and ________________________ _____ _____

Inferred positions of Earth’s Landmasses

Major Geologic Events(ex. Ice ages & Orogenys)

The study of geologic time allows us to reconstruct Earth’s history, gaining a sense of the world before

humans and allows us to possibly predict events and conditions of the future.

An ________ is the process of mountain building

TURN TO PAGES 8 & 9 IN YOU ESRT!

Orogeny

GEOLOGIC EVENTS OF THE PAST:

_________ causes gaps in the geologic record.

Erosion

When a new layer of rock is laid down on a surface that has been _______ it forms a buried erosional surface or an

___________________Eroded,

unconformity

NEWBOTTOMLAYER APPEARS(EMERGES)

LAYER CIS MISSINGEROSION

EROSION

THE UNCONFORMITY IS THE BURIED EROSIONAL SURFACEBETWEEN B AND D

Who’s Younger?How Do You Know??

Relative vs. Absolute Relative vs. Absolute DatingDatingFive family members’ ages are compared:

Anthony is the youngest.Melanie is 4 years old. Michael is older than Susan. Susan is 16 years old. Ashley is older than Melanie, but younger than Susan.

Give the order of the family members from oldest to youngest. Also, which descriptions give relative ages and which give absolute ages?

MichaelSusanAshley

MelanieAnthony

Age of rock or geological event in years before the present (as opposed to relative ages).

Common units are:millions of years ago = m.y. = 106

billions of years ago = b.y. = 109

How do scientists find absolute ages?

What were some of the techniques used to determine

absolute time prior to the discovery of radioactivity.

Tree RingsVarves

Modern science now uses Radioactive Isotopes to find the absolute age of a given material (rock, fossil, etc.).

Mass spectrometer – instrument used in the detection and study

of isotopes

VII. RADIOACTIVE DATING:

A. Fossils enabled geologists to give ___________ time,relative

Relative Time

Compares rock ages to _______________.

Ex: The Limestone is older than the Sandstone.

each other

However, B. Measurements of natural ___________in ( metamorphic and igneous) rocks have allowed the _________ time scale to be an ________ time scale. geologic

absolute

radioactivity

The _________ _____ of an object is measured in years.

Ex: The limestone formed 5 mya and the sandstone formed 2 mya

absolute age

C. Chemical elements often have several forms called _______________isotopes

• Let’s review some basic chemistry so that we can obtain a better understanding of this technique.

Let’s review the

structure of an atom

The basic building

block of matter

An element is a substance consisting of atoms that are chemically alike (# of protons).

Most elements exist in several different types of isotopes (atoms with a different number of neutrons in their nuclei).

Examples: Carbon isotopes, C-12 & C-14

The nucleus (containing neutrons and protons) of radioactive isotopes are unstable and over time they will emit particles and electromagnetic energy.

This is known as Radioactive Decay, and changes the radioactive isotope into other isotopes or atoms. This occurs until, a stable isotope forms.

The rate of decay (breakdown) for any radioactive isotope is constant.

Over a given period of time, a definite fraction of the atoms of an isotope will decay.

ISOTOPE:An unstable element with different number of neutrons than a normal (stable) element. (Its unstable so wants to change to stable)

EX.

C C6 612 14

6 protons 6 protons6 neutrons

Unstable

8 neutrons

EX.

C C6 612 14

6 protons 6 protons6 neutrons 8 neutrons

unstable

D. If the nucleus has more or fewer than the

normal number of ____________, the isotope

may be ____________

neutrons

radioactive(unstable)

E. A radioactive isotope will break down naturally into a lighter element called

_____ ________ which is stable.

decay product

This process is called…

Radioactive Decay

RADIOACTIVE DECAY:

WHEN AN UNSTABLE ________ ELEMENT CHANGES INTO A COMPLETELY DIFFERENT (BUT STABLE) __________ ELEMENT

DAUGHTER

PARENT

F. A sample starts out at “Time zero” with _______ Percent of radioactive material.

100

Time Zero: when the sample is originally formed by cooling or solidification of igneous or metamorphic rock

As time goes by and the sample gets older, the radioactive element decay, and _______ radioactive atoms remain in the sample.

fewer

Therefore, the higher the ratio of decay product to the radioactive element, the _____ the sample.

older

The ratio between the mass of the radioactive element and its decay product in a sample is the _______________decay product ratio

G. The decay of the parent atoms in a sample to daughter atoms is a _________ process…

random

That happens at _____________ rates for different radioactive elements. Lets model this with pennies…

different

H. The rate of decay of a radioactive element is measured by its’ _______ _________half life

HALF-LIFE:THE AMOUNT OF TIME IT TAKES FOR

HALF OF THE UNSTABLEATOMS IN A SAMPLE TO CHANGE TO THE STABLE DECAY PRODUCT

Original=100%

Decay product=0%

100/0Or 1 to 0

Original=50%

Decay product=50%

50/50 Or 1 to 1

After one Half-life:

Original=25%

Decay product=75%

25/75Or 1:3

After two Half-lives:

Original=12.5%

Decay product=87.5%

12.5/87.5

After three Half-lives:

Original=6.25%

Decay product=93.75%

6.25/93.75

After four Half-lives:

The time required for half of the atoms in a given mass of an isotope to decay is known as the half-life of the isotope.

Each radioactive isotope has its own characteristic half-life, which is not affected by any environmental factors (To, P, or chemical reactions), mass or volume.

The method of using the half-life of a radioactive isotope to determine the absolute age of a material.

The ratio between the amount of the original isotope (Parent Material) and the amount of its decaying product (Daughter Product), is used to establish the absolute age of a sample.

“Daughter Product”

“Parent Material”

Key

Other C14 N14

Carbon Dating0 Half-Life

0102030405060708090

100

0 1 2 3 4 5 6

Number of Half-Lives

Perc

ent o

f Ele

men

ts

% C14% N14

Key

Other C14 N14

Carbon Dating1 Half-Life (5,700 years)

0102030405060708090

100

0 1 2 3 4 5 6


Perc

ent o

f Ele

men

ts

% C14% N14

Key

Other C14 N14

Carbon Dating2 Half-Lives (11,400 years)

0102030405060708090

100

0 1 2 3 4 5 6


Perc

ent o

f Ele

men

ts

% C14% N14

Key

Other C14 N14


0102030405060708090

100

0 1 2 3 4 5 6


Perc

ent o

f Ele

men

ts

% C14% N14

(ESRT, pg. 1)Which isotope has the shortest half life? Longest?

1/16

1/32

1/64

22,800

28,500

34,200

How many Potassium-40 half lives have passed if there are 3 times more Argon-40 atoms than Potassium-40 atoms? What if there are 3 times as many Potassium-40 atoms?

Igneous and metamorphic rocks work excellent for radioactive dating because at the time of crystallization (or recrystallization), a specific ratio of stable and radioactive isotopes are incorporated into the crystals.

On the other hand, sedimentary (clastic) rocks do not work well because they are composed of older, pre-existing rock fragments.

Imagine a rock forms with zircon mineral grains containing U238 and no Pb206.

Basic Facts on this Isotope

• Half Life of Uranium-238 (U238) = 4.5 * 109 yr

• U238 decays to become Lead-206 (Pb206)

Decay of U-238

If this rock were to be found today, and contained a 1:1 ratio, equal quantities of both U238 to Pb206, it would be concluded that the rock formed 4.5 b.y. How old would the sample be if it had a 1:3 ratio of U-238 to Pb-206?

Radioactive isotopes with very long half-lives are excellent for dating very old rocks, but for younger objects, isotopes with shorter half-lives are better at the finding absolute age.

One such isotope is Carbon-14 (C14), with a half-life of 5,700 years.

Carbon-14 (C14)Carbon-14 dating – also called radiocarbon dating – can be used to date remains that contain carbon up to 70,000 years old.

This method has been used to date early humans, mastodonts, and many other geologically “recent” organic remains.

Let’s examine the breakdown of Carbon-14

1 Carbon-14 C14

2 Potassium-40 K40

3 Uranium-238 U238

4 Rubidium-87 Rb87

N14

Ar40

Pb206

Sr87

5.7 x 103

1.3 x 109

4.5 x 109

4.9 x 1010

Element Decay Product Half-life

“Time Zero” for carbon dating begins when the organism ___________ or when the ________ burns out.

dieswood fire

H. Calculating the age of a rock:

1. What would be the age of the rock if it has equal amounts of C-14 and its decay product N-14?

One half life has gone by

5.7 x 103 yearsor 5,700 years

2.What % of the sample is radioactive after the following half-lives,

1 half-life2 half-lives3 half-lives

50%25%12.5%

3. After 11,200 years how much C-14 would remain in a 10 gram sample?

25% or 2.5 grams1/4 of the original amount

I. Selecting the Best Radioactive Element:

1. Under 50,000 years

2. Over 50,000 years

Use Carbon-14

Use Uranium-238

Carbon 14 is used for dating

organic materialAnd ancient wood fires

State the best isotope to use to discover the age of the individual “caught off guard” in the cartoon below. Why?

The following diagram represents a cross-sectional view of a portion of Earth’s crust showing

sedimentary rock layers that have not been overturned. The letters identify the specific layers.

Which rock layer is the oldest? Youngest?

What is represented by line A-B?

List the rock layers from oldest to youngest.

A, D, C, E, B

C

DE

BA

G

FH

I

C

DE

G

F

BA

HI

What is the evidence that indicates the fault is the most recent geologic event to have

occurred in this area?

What is the evidence that indicates rock layer B is younger than layers A and C?

E D B A C

• What is the definition of a half life?

• Of the radioactive isotopes listed on the front of the ESRT, which one has the longest half life?

The time required for half of the atoms in a given mass of a radioactive isotope to decay

Rubidium-87

Review Book Multiple Choice Problems1. 1

2. 2

3. 3

4. 3

5. 1

6. 2

7. 3

8. 1

9. 4

10. 3

11. 1

12. 3

13. 2

14. 4

15. 4

Decay of Marsium Isotope

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8 9

Trial Number

% o

f Iso

tope

% Remaining % Decayed

Take out your Marsium Lab

1 half-life

E D B A C

•Superposition

•Cross-Cutting Relationships

•Unconformities

•Contact Metamorphism

•Uniformity of Process

Thanks to the collective resources of ESPRIT for

contributing images

Design via Threadless

Practice: what happened here?

Practice Geologic Profiles

Look at the geologic profiles, write down what you think is the correct sequence of events. Then click the mouse to advance the presentation. Repeat this process for each of the profiles.

Profile 1

Ss with fishLsSsShLs

Sequence of Events

Remember the law of superposition.

Oldest

Youngest

Profile 2

SsLsCnglShFaultingSs

Sequence of EventsFaults are younger than

the rock they are in.

How do you know there is a fault? Look for the same rock layers. They do not line up.

Profile 3

Ss with fishLsSsShLs IntrusionTilting, uplifting, erosionSubsidence (sinking)CnglShSs with fishSsLsSh

Sequence of Events

Do you know what this is?

An unconformity!

These two steps formed it.

Remember this a buried erosional surface

Profile 4

ShSs with fishCnglLsFoldingIntrusion and Extrusion

Sequence of Events

Intrusions and extrusions are younger than the rock

they are in.

Metamorphic rock tells you whether you have an

intrusion or an extrusion.

Profile 5

ShSsCnglSs with fishLsIntrusionUplifting

Sequence of Events

Magma was forced in between the existing layers of rock to create this

formation.

You know it is an intrusion because…

Metamorphic rock is on all sides.

Exposed volcanic ash layers in Alaska provide an excellent unit for correlation and establishing ages for geologic units and events

What are the characteristics of a good index fossil? (You must know 2)

Explain why volcanic ash deposits make good index layers for rock correlation?

Fossils of organisms that lived for a short period of time over a wide geographic area

Volcanic ash deposits cover a large geographic area in a relatively short period of time

Take out a pencil, ESRT and calc.

QUIZ TIME!

What is longer unit of time, a geologic era or a period?

What geologic period of time are we in today? Epoch?

An Era is larger and they are broken up into Periods

Quaternary Period, Holocene Epoch

Which geologic period ended with the extinction of many kinds of marine animals, including trilobites?

Which orogeny was caused by the collision of North America and Africa along a transform margin creating Pangaea?

The Permian Period

The Appalachian (Alleghanian) Orogeny

The Devonian aged siltstone shown in the photograph below occurs as surface bedrock in Hamilton, NY. What does the presence of the fossil suggest about the environment of Hamilton during the Devonian?

The table below gives information about the radioactive decay of carbon-14. Part of the table has been deliberately left blank for student use. After how many years will 1/128 of the original carbon-14 remain?

State one method used to correlate rock layers…

State one piece of evidence why the limestone is the most resistant rock layer in the outcrops.

Comparing rock texture / composition, looking for index fossils, examining

sequencing of strata

The limestone unit extends the furthest out of the

outcrop (cliff)

What does the discovery of Ordovician aged fossil corals in the surface bedrock of NYS cause you to infer?

Parts of NYS were once in a shallow, warm marine envrionment

Geologic History Powerpoint Notes

Technology

Transcript of Geologic History Powerpoint Notes