interpreting geological history aim geohis 1a - how old is mr. foley relative to the planet earth?
TRANSCRIPT
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
Some examples of Correlations
In the following diagram at the right
Give the order of the layers produced
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
Some examples of Correlations
In the following diagram at the right
Give the order of the layers produced
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!
Other Evidence of Mountain Building
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
Other Evidence of Mountain Building
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
Sed Rock Layer 2 myo
Sed Rock Layer 3 myo
Sed Rock Layer 4 myo
Sed Rock Layer 5 myo
Sed Rock Layer 2 myo
Sed Rock Layer 3 myo
Sed Rock Layer 4 myo
Sed Rock Layer 5 myo
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?