Exam 2
Tuesday December 3, 2013 6:05-7:45 pm, rm. 1310N
• Exam 2 will cover the Fourth Dimension and Plate Tectonics.
• You will only need a pen or pencil (calculator optional).
•There will be 50 questions (about 25 per section).
• Format will be multiple choice/T-F with extra credit fill in.
•It would be to your benefit to use assignment 3 and 4 as a study guide!!
**The powerpoint is a guide to help with studying but please be aware unless
we say it is NOT on the exam then it is fair game**
Plate Tectonics
http://www.brooklyncollegegeology.com/plates/platesindex.html
•
Know the different types of plate boundaries and what geologic features occur at
those boundaries (e.g. , convergent, divergent, mountains, volcanoes)
•
Understand what geologic processes occur at each of the plate boundary types
(e.g. , rifting, subduction)
•
Review how Wegner devised his theory of “continental drift”
•
Understand how geologist investigate the interior of the Earth
•
Know what the different layers of the Earth are
•
Know the difference between the focus and epicenter of an earthquake
You will not be asked to determine rate of plate movement or magnitude of an
earthquake
Example of what you would need to identify
Answers:
A. Ocean trench formed at a
convergent boundary
B. Volcanic mountain range
A
C
C. The process of subduction
occurring as the oceanic crust
sinks beneath a the
continental crust back to the
mantle.
This is an example of what you should be
able to identify. Review the diagrams on
plate tectonic site.
http://www.brooklyncollegegeology.com/plates/platetec14.htm
The Fourth Dimension
Environments of Rock Formations: Igneous Rocks
In a Lava flow
http://www.brooklyncollegegeology.com/fourth/volc_rollover/volc_rollovera.html
In a magma chamber
http://www.brooklyncollegegeology.com/fourth/crystallization_rollover/crystallization_rollover.html
•Understand the process igneous (volcanic) rocks undergo in a magma chamber and
lava flow
•What factors affect the size of crystals in igneous rocks?
•How do rocks behave when heated due to deformation in comparison when they are
cold?
•Difference between vesicular and non-vesicular lava and where are they found?
The Fourth Dimension
Environments of Rock Formations: Metamorphic Rocks
►Understand the process metamorphic rocks undergo when heat
and pressure are applied
http://www.brooklyncollegegeology.com/fourth/meta_rollover/meta_rollover.html
Environments of Rock Formations: Sedimentary Rocks
► Lithification vs Cementation
http://www.brooklyncollegegeology.com/fourth/diagen_rollover/diagen_rollover.html
http://www.brooklyncollegegeology.com/fourth/cement_rollover/cement_rollover.html
(Nothing on Salt water lakes or Hypersaline conditions)
Determining Rock Origin
Four Clues to determine a rocks origin:
•
Mineralogy of the rock: the minerals that the rock contains.
•
Texture of the rock: the sizes, shapes and arrangement of the grains.
•
Structure of the rock: larger scale features, such as layering or
discontinuities.
•
Field relationships: the size and shape of the rock body and how it relates to
other rock bodies.
http://www.brooklyncollegegeology.com/fourth/rock_origin_determine.html
Rock Mineralogy: Igneous Rocks
►You will be responsible to determine percentages of minerals using the mineral
Assemblage Chart (a).
► Chart (b) is an example of how to read the mineral assemblage chart. See link for
specific details.
(a)
(b)
Mineral
From
To
Length
Calcium
rich
feldspar
0%
20%
20%
Pyroxene
20%
38%
18%
Olivine
38%
100%
62%
TOTAL
100%
Example Question: Based on chart (b), a rock with composition “Y” contains how much feldspar?
Ans. 20 %
http://www.brooklyncollegegeology.com/fourth/rock_comp_igneous.html
Rock Mineralogy: Continued
Review and have an understanding on the Sedimentary, Metamorphic and the
conclusions sections.
This information sets the groundwork for the following sections.
Sedimentary : http://www.brooklyncollegegeology.com/fourth/rock_comp_sedimentary2.html
Metamorphic: http://www.brooklyncollegegeology.com/fourth/rock_comp_metamorphic.html
Rock Texture
Understand the differences in the texture of igneous, metamorphic and
sedimentary rocks.
For example: If a geologist finds in the field a rock with poorly sorted grains with
a clastic texture what class of rock would it belong too?
Answer: sedimentary
Specific terms to know:
•Clastic (rocks)
•Crystalline (rocks)
•Glass (volcanic)
•Vesicular vs Non vesicular
http://www.brooklyncollegegeology.com/fourth/rock_texture.html
Rock Structure
Read and have an understanding of:
Primary Structures: Layering 1, 2 and other Primary Structures
http://www.brooklyncollegegeology.com/fourth/layering1.html
http://www.brooklyncollegegeology.com/fourth/layering2.html
http://www.brooklyncollegegeology.com/fourth/useful_structures.html
Secondary Structures
-Be sure to review rollovers discussing deformation and plate tectonics.
http://www.brooklyncollegegeology.com/fourth/secondary_structures.html
http://www.brooklyncollegegeology.com/fourth/deformation_rollover/deformation_rollover.html
Field Relationships
Origin of Slaty Cleavage
Ex. What can occur near the contact between an igneous intrusive body and
sedimentary rock?
Ex. What are the metamorphic equivalents of shale?
http://www.brooklyncollegegeology.com/fourth/slaty_cleavage.html
http://www.brooklyncollegegeology.com/fourth/slaty_cleavage_origin.html
Origin of Cross-Cutting Rock Bodies
•Review and have an understanding
•What type of evidence will you find near alteration zones?
http://www.brooklyncollegegeology.com/fourth/cross_cutting.html
http://www.brooklyncollegegeology.com/fourth/froshlec8.html
Field Relationships--continued
Igneous Origin
--Review and have an understanding
http://www.brooklyncollegegeology.com/fourth/lava_sill.html
Metamorphic Origin
--Review “scenarios” of plate tectonic examples and metamorphism
http://www.brooklyncollegegeology.com/fourth/field_meta.html
Sedimentary Origin
--Review and have an understanding
http://www.brooklyncollegegeology.com/fourth/field_sed.html
Rocks and Earth’s History: Relative Age
► Know the definition and understand the differences between each of these
concepts
Law of: Superposition
Lateral Continuity
Cross-cutting Relationships
Original Horizontality
Biotal Succession
The use of primary structures:
•How could you determine the top side of a rock vs. the bottom side using
primary structures?
http://www.brooklyncollegegeology.com/fourth/froshlec8.html
DECIPHERING A SAMPLE OF EARTH HISTORY
You will be given an example very similar to this and have to determine:
The sequence of events
Be able to apply the appropriate law to support sequence of events (see previous slide)
ex. The relative age of Intrusion C and fault F-F can be determined by?
Ans. Cross-cutting relationships. http://www.brooklyncollegegeology.com/fourth/froshlec8.html
determine the age of a layer based on information given http://www.brooklyncollegegeology.com/fourth/froshlec10.html
Yes, just like from your
homework assignment….
Unfolding the Earth’s History
The Doctrine of Uniformitarianism:
http://www.brooklyncollegegeology.com/fourth/froshlec11.html
Absolute Age
We are only testing you on Radiometric dating from this page BUT you should still read the
other sections as it may help connect other topics from previous sections.
Use the Radiometric dating supplement in the following slides as your study guide not the
website!!
**Understand the difference between absolute age and relative age.
http://www.brooklyncollegegeology.com/fourth/froshlec9.html
You are not responsible for Other absolute age dating techniques or the science–creationist controversy.
Radiometric Dating
When calculating the age of a rock using radiometric dating we can create a
table to better see the incremental changes between the parent-daughter ratio.
This is an explanation of the construction of the table presented from the
website.
On the exam you will be responsible to answer 4 questions in regards to
radiometric dating by filling in blank portions of the chart.
What is half-life?
When a radioactive element decays, a parent element is converted to its stable daughter
element.
In the U-Pb system, a radioactive atom of uranium decays to become a stable atom of
lead. Radioactive dating employs the idea of the half-life. This is the amount of time
required for a given number of radioactive atoms to decay to one half its original number,
being replaced by the same number of stable daughter atoms.
Each radioactive system has a unique half-life. In the case of the U-235/Pb207 system,
the half life is 704 million years. For the sake of argument, if we began with 100 atoms
of radioactive U-235, after 704 million years or one half life, we would have 50 atoms of
U-235 and 50 atoms of Pb-207. In another 704 million years, or in 1408 million years
after starting time, the 50 U-235 atoms would have again decayed to half their original
number, 25, being replaced by another 25 daughter atoms of Pb-207. The ratio of
parent to daughter atoms after 2 half-lives would be 25:75 or 1:3.
Radiometric Dating
Example 1:
After careful analysis, a geochronologist determines that an unweathered, unmetamorphosed mineral
sample contains 8 trillion atoms of the radioactive element U-235 and 504 trillion atoms of its decay
product Pb-207 (half life of U-235 is 704 million years).
1st Distinguish the parent from the daughter
Sample contains 8 trillion atoms of the parent (radioactive element) U-235
Sample contains 504 trillion atoms of the daughter (decay product) Pb-207
2nd Determine the parent/daughter ratio
Divide the number of daughter atoms over the number of parent atoms to get the following:
504/8= 63 for a parent to daughter ratio of 1:63.
So for every 1 parent atom we have 63 daughter atoms giving us a 1:63 ratio parent-daughter ratio.
By referring to the table (next slide) we can figure out how my half-lives or years it takes to get the
1:63 parent-daughter ratio.
Calculating Parent:Daughter ratios
Parent U-237
Daughter Pb-207
Fraction of total
represented by
parent:daughter
Parent/ Daughter
ratio
Half life
Time Elapsed
1000
0
1/1:0/1
1:0
0
0
500
500
1/2:1/2
1:1
1
704
250
750
1/4:3/4
1:3
2
1408
125
875
1/8:7/8
1:7
3
2112
62.5
937.5
1/16:15/16
1:15
4
2816
31.25
968.75
1/32:31/32
1:31
5
3520
15.625
984.375
1/64:63/64
1:63
6
4224
Half life of Uranium is 704 million years
Line 1: When a new radioactive mineral crystallizes, we assume it has only parent (radioactive) atoms. The ratio
parent:daughter is 1:0
Line 2: One half-life has elapsed, so the original number of radioactive atoms is reduced by half and replaced by an
equal number of daughter atoms. The ratio parent:daughter is 1:1. The process has taken 704 million years.
Line 3: Two half lives have elapsed. The fraction of parent atoms at one half life is again reduced by one half and is now
¼ of the original number while daughter atoms are ¾. The parent daughter ratio is 1:3 and the process has taken 2 x
704 million years or 1408 million years.
Our sample has a parent:daughter ratio of 1:63, telling us that 6 half-lives or 4224 million years have elapsed since the
radioactive mineral crystallized
Radiometric Dating
Example 2
A piece of bone contains 7 trillion atoms of Carbon 14 and 105 trillion atoms of its
decay product Nitrogen 14 (half life of Carbon is 5,730 years).
1st Distinguish the parent from the daughter:
Sample contains 7 trillion atoms of the parent (radioactive element) C-14
Sample contains 105 trillion atoms of the daughter (decay product) N-17
2nd Determine the parent/daughter ratio:
Divide the number of daughter atoms over the number of parent atoms to get the
following: 105/7=15 Parent-daughter ratio is 1:15
Now we work consult an appropriate table to determine
how many half-lives must elapse to create this parent
daughter ratio and how much time is represented
Radiometric Dating
Parent C-14
Daughter N-14
Parent/ Daughter
ratio
Half life
Time Elapsed
1
0
1:0
0
0
1/2
1/2
1:1
1
5730
1/4
3/4
1:3
2
11460
1/8
7/8
1:7
3
17190
1/16
15/16
1:15
4
22920
In the C-14 system, one half-life is 5,730 years
As in the previous example you find the line in the table with the parent-daughter ratio
determined from your question (1:15)
This ratio corresponds to 4 half-lives or 22,920 years, the age of our sample