Exam 2 sp10

The Fourth Dimension

Exam 2 May 5th 2010 from 6:05-7:45 pm in room 3127N. All you need is a pen or pencil (preferred) calculator is optional.

•Please focus on topics in mentioned in this review.

•At the top of each slide will have the name of the section from the main Fourth Dimension page (http://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/rocks_home.html)

•There will be approximately 30 questions on the Fourth Dimension (multiple choice and T/F).

•It would be to your benefit to use assignment 4 as a study guide!!

•If you encounter any broken links or questions regarding the PowerPoint please contact Michelle.

How do rocks form?

Review the difference between attachment by intergrowth vs attachment by cementation.

http://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/rocks_home.html

Environments of Rock Formation

Igneous Rocks

Understand the process igneous rocks undergo in a magma chamber and lava flow

In a Lava flowhttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/crystallization_rollover/crystallization_rollover.html

In a magma chamberhttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/volc_rollover/volc_rollovera.html

--When will you have finer grain igneous rocks vs. coarser grain igneous rocks?--How do rocks behave when heated in comparison when they are cold?--Difference between vesicular and non-vesicular rocks and where are they found?

Metamorphic Rocks

Understand the process metamorphic rocks undergo when heat and pressure are appliedhttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/meta_rollover/meta_rollover.html

Mineral Assemblages

►You will be responsible to determine percentages of minerals using the mineralAssemblage 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://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/rock_comp_igneous.html

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://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/rock_origin_determine.html

Rock Texture

Understand the differences in the texture of igneous, metamorphic and sedimentary rocks.

Terms to know: Texture, Crystalline, Clastic, glass, vesicular, non-vesicular,

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://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/rock_texture.html

Rock Structure

Review and have an understanding of the 4 sections.

Primary structures-Layering 1, 2, other primary structures and secondary structures

http://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/rocks_home.html

http://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/useful_structures.html

Field Relationships

Origin of Slaty CleavageEx. What can occur near the contact between an igneous intrusive body and sedimentary rock?Ex. What is the metamorphic equivalent of shale?http://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/slaty_cleavage_origin.html

Origin of Cross-Cutting Rock Bodies: review and have an understandinghttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/cross_cutting.html

Igneous Origin: review and have an understandinghttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/lava_sill.html

Metamorphic Origin: Review “scenarios” of plate tectonic examples and metamorphismhttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/field_meta.html

Sedimentary Origin: review and have an understandinghttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/field_sed.html

Conclusions: review and have an understandinghttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/rocks_conclusions.html

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 (fossil assemblage)

THE USE OF PRIMARY STRUCTURES--How could you determine the top side of a rock vs. the bottom side using primary structures?

http://depthome.brooklyn.cuny.edu/geology/onlinecore/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

--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 givenhttp://depthome.brooklyn.cuny.edu/geology/onlinecore/fourth/froshlec10.html

A supplement to Radiometric DatingA 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 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. http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/froshlec9.html

Radiometric DatingRadiometric 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 DatingRadiometric 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

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)

Half life of Uranium is 704 million years

Radiometric DatingRadiometric DatingParent U-235

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

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= 1:3Line 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).

1st Distinguish the parent from the daughter:Samples contains 7 trillion atoms of the Parent (radioactive element) C-14Sample 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.

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

Radiometric Dating

Radiometric DatingRadiometric 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

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.

Plate Tectonics

Know the different types of plate boundaries and what geologic features occur at those boundaries (e.g. , convergent, divergent, mountains, volcanoes) http://depthome.brooklyn.cuny.edu/geology/onlinecore/plates/platetec14.htm

Understand what geologic processes occur at each of the plate boundary types( e.g. , rifting, subduction) http://depthome.brooklyn.cuny.edu/geology/onlinecore/plates/platetec16.htm

Review how Wegner devised his theory of “continental drift”. http://depthome.brooklyn.cuny.edu/geology/onlinecore/plates/platetec1.htm

Understand how geologist investigate the interior of the Earth.

Know what the different layers of the Earth are. http://depthome.brooklyn.cuny.edu/geology/onlinecore/plates/platetec12.htm

**You WILL NOT be asked to determine the epicenter, focus or magnitude of earthquakes.