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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
Sedimentary layers
Sedimentary layers
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
The extrusion came after the lowerlayers were formed but….Before the top layer
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
The extrusion came after the lowerlayers were formed but….Before the top layer
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
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)
Law of Original Lateral Continuity
Law of Original Lateral Continuity
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
Number of Half-Lives
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
Number of Half-Lives
Perc
ent o
f Ele
men
ts
% C14% N14
Key
Other C14 N14
Carbon Dating3 Half-Lives (17,100 years)
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 Dating4 Half-Lives (22,800 years)
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 Dating5 Half-Lives (28,500 years)
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 Dating5 Half-Lives (28,500 years)
0102030405060708090
100
0 1 2 3 4 5 6
Number of Half-Lives
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: what happened here?
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
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