Final Review – Part 2
The Fourth Dimension
Please focus on topics in mentioned in this review.
There will be approximately 25 questions on the Fourth Dimension
(mult.choice/T-F).
It would be to your benefit to use assignment 4 as a study guide!!
We want all of you to be prepared for the exam but DO NOT OVER-STUDY.
Final Exam Review – Environments of Rock Formation
In a Lava flow
Igneous Rocks
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/crystallization_rollover/c
rystallization_rollover.html
In a magma chamber
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/volc_rollover/volc_rollov
era.html
--When will you have finer grains rocks vs. coarser grain igneous rock?
--How do rocks behave when heated in comparison when they are cold?
--Difference between vesicular and non-vesicular and where are they
found?
Final Review--Environments of Rock Formation
► Understand the process sedimentary rocks undergo in a salt
water lake environment
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/rocks_origin_intergrow
th.html
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/salt_solution_rollover/s
alt_solution_rollover.html
►Understand the process igneous rocks undergo in a magma
chamber and lava flow
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/crystallization_rollover/cry
stallization_rollover.html
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/volc_rollover/volc_rollover
a.html
►Understand the process metamorphic rocks undergo when
heat and pressure are applied
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/meta_rollover/m
eta_rollover.html
Final Exam Review -- Mineral Assemblages
►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.
(b)
(a)
Example Question: Based on chart (b), a rock with
composition “Y” contains how much feldspar?
Ans. 20 %
http://academic.brooklyn.cuny.edu/geology/leveson/cor
e/topics/rocks/rock_comp_igneous.htm
Mineral
From
To
Length
Calcium
rich
feldspar
0%
20%
20%
Pyroxene
20%
38%
18%
Olivine
38%
100%
62%
TOTAL
100%
Final Review--Determining Rock Origin
--Look at the mineralogy of the rock: the minerals that the rock contains.
--Look at the 'texture' of the rock: the sizes, shapes and arrangement of
the grains.
--Look at the 'structure' of the rock: larger scale features, such as layering
or discontinuities.
--Look at field relationships: the size and shape of the rock body and how
it relates to other rock bodies.
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/rock_orig
in_determine.html
Final Review – 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? Ans.
sedimentary
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/rock_texture
/rock_texture.html
Final Exam Review – Field Relationships
Origin of Slaty Cleavage
Ex. What can occur near the contact between an igneous intrusive body
and sedimentary rock?
Ex. What is the metamorphic equivalent of shale?
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/field_relationships/slaty
_cleavage_origin.html
Origin of Cross-Cutting Rock Bodies
--review and have an understanding
Igneous Origin
--review and have an understanding
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/field_relationships/lava_
sill.html
Metamorphic Origin
--Review “scenarios” of plate tectonic examples and metamorphism
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/field_relationships/field
_meta.html
Final Exam Review – Relative Age
► Know the definition and understand the differences between
each of these concepts
LAW OF SUPERPOSITION
LAW OF LATERAL CONTINUTIY
LAW OF CROSS-CUTTING RELATIONSHIPS
LAW OF ORIGINAL HORIZONTALITY
THE LAW OF 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://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/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
--appropriate law (ex. The relative age of Intrusion C and fault F-F can
be determined by? Ans. Cross-cutting relationships.)
--determine the age of a layer based on information given
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/froshlec10.ht
ml
A supplement to 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 parentdaughter 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.
http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/froshlec9.html
Radiometric Dating
Follow this example: 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 Uranium is 704 million years
1st:Distinguish the parent from the daughter:
Samples 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
So for every 1 parent atom we have 63 daughter atoms giving us a 1:63 ratio
parent-daughter ratio. By creating the table we can figure out how my half-lives
or years it take to get the 1:63 parent-daughter ratio.
Radiometric Dating
Parent U-237
Daughter Pb-207
Parent/ Daughter
ratio
Half life
Time Elapsed
1
0
1:0
0
0
1/2
1/2
1:1
1
704
1/4
3/4
1:3
2
1408
1/8
7/8
1:7
3
2112
1/16
15/16
1:15
4
2816
1/32
31/32
1:31
5
3520
1/64
63/64
1:63
6
4224
Half life of Uranium is 704 million years
Line 1: The table always begins with 1 parent and 0 daughter giving you a 1:0 ratio.
Line 2: Next take HALF of the parent from previous line (half of 1 is ½). The numerator will give you the
parent portion of the ratio (which will always be 1).
Line 2: Then to get the daughter portion complete the fraction to equal 1 ( ½ + ½ =1). The numerator of
the daughter fraction will give you the second half of the parent-daughter ratio.
Line 2: This means 1 half life has occurred.
Line 2: Time Elapsed is increased by the years of the half life (in our case is 704 million years)
Radiometric Dating
Parent U-235
Daughter Pb207
Parent/
Daughter ratio
Half life
Time Elapsed
1
0
1:0
0
0
1/2
1/2
1:1
1
704
1/4
3/4
1:3
2
1408
1/8
7/8
1:7
3
2112
1/16
15/16
1:15
4
2816
1/32
31/32
1:31
5
3520
1/64
63/64
1:63
6
4224
Repeat the procedure described in the previous slide to complete the table until
you have reached the ratio you determined in the initial question (1:63).
Line 3: Parent= half of Line 2 (half of ½ = ¼)
Line 3: Daughter = 1- ¼ = ¾
Line 3: Ratio= 1:3
Line 3: Add 1 to the previous half life (1+1=2)
Line 3: Time Elapsed= 704+704=1408
The ratio 1:63 tell us that 6 half lives have passed corresponding to 4224 million years
or 4.2 billion years. (Remember that a million has 6 places, and billions has 9).
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:
Samples 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 out a table until we reach the 1:15 ratio.
Radiometric Dating
Parent C14
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
Following the procedure from the previous example you complete the table until
you hit the parent-daughter ratio determined from your question (1:15)
We then noticed that to have a ratio of 1:15 4 half lives had passed
equivalent to 22,920 years, so the bone is more or less that age.