Exam 2 Tuesday December 3, :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 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 C. The process of subduction occurring as the oceanic crust sinks beneath a the continental crust back to the mantle. C A This is an example of what you should be able to identify. Review the diagrams on plate tectonic site.

The Fourth Dimension Environments of Rock Formations: Igneous Rocks In a Lava flow In a magma chamber 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 Environments of Rock Formations: Sedimentary Rocks ► Lithification vs Cementation (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.

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) MineralFromToLength Calcium rich feldspar 0%20% Pyroxene20%38%18% Olivine38%100%62% TOTAL100% Example Question: Based on chart (b), a rock with composition “Y” contains how much feldspar? Ans. 20 %

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 : Metamorphic:

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

Read and have an understanding of: Primary Structures: Layering 1, 2 and other Primary Structures Secondary Structures -Be sure to review rollovers discussing deformation and plate tectonics. Rock Structure

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? Origin of Cross-Cutting Rock Bodies Review and have an understanding What type of evidence will you find near alteration zones?

Igneous Origin --Review and have an understanding Metamorphic Origin --Review “scenarios” of plate tectonic examples and metamorphism Sedimentary Origin --Review and have an understanding Field Relationships--continued

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?

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.  determine the age of a layer based on information given Yes, just like from your homework assignment….

The Doctrine of Uniformitarianism: Unfolding the Earth’s History

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. You are not responsible for Other absolute age dating techniques or the science–creationist controversy. Absolute Age

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). 1 st 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 nd 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-237Daughter Pb-207 Fraction of total represented by parent:daughter Parent/ Daughter ratio Half lifeTime Elapsed /1:0/11: /2:1/21: /4:3/41: /8:7/81: /16:15/161: /32:31/321: /64:63/641: 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 Half life of Uranium is 704 million years Remember our goal is to get to this ratio

Radiometric Dating 1 st 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 2 nd 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 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 Parent C-14Daughter N-14 Parent/ Daughter ratio Half lifeTime Elapsed 101:000 1/2 1: /43/41: /87/81: /1615/161: 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