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The Case Study Method for the Assessment of Student Learning: Using Scientific Reasoning and Deep Geological Time to Predict Future Environmental Impacts.

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Presentation on theme: "The Case Study Method for the Assessment of Student Learning: Using Scientific Reasoning and Deep Geological Time to Predict Future Environmental Impacts."— Presentation transcript:

1 The Case Study Method for the Assessment of Student Learning: Using Scientific Reasoning and Deep Geological Time to Predict Future Environmental Impacts Chen Zhu Geological Sciences and School of Public and Environmental Affairs Brooke A. Treadwell Educational Leadership and Policy Studies Thank you Jeff for the introduction. It is always a great pleasure to be here.

2 Acknowledgements Departmental colleagues, Simon Brassell, Claudia Johnson, Michael Hamburger, Jim Brophy, Bruce Douglas for sharing interests and discussions Lilly Freshmen Learning Project leaders Joan Middendorf, David Pace, and Simon Brassell and “cohorts” Collaborators for this research project: George Rehrey and Claudia Johnson

3 The Teaching and Learning Problem
Often, the immensity of deep geological time (DGT) is very difficult for non-science majors to understand and to use when applying it to geological problems DGT can be both a bottleneck and a threshold concept for many science classes DGT is important for student success within Geology and other sciences (Hawkins 1978) Prepare scientifically literate, informed citizens to vote in elections that will impact environmental policy on high-stakes issues such as climate change/the carbon tax and nuclear waste disposal. In my first class, I always tell my students. They are 18 to 20 years old. They will vote in more than 15 presidential elections. In some elections, environmental issues like global warming and nuclear waste disposal can be prominent. Scientific and environmental literacy can help them become more informed citizens. Some scientists argue we have tens of millions among the 300 million population who are has the scientific literacy, we have a more chances to arrive reasonable and sound solutions to some very complex problems. Indiana University – Bloomington is a good case in point. At IU, we have a large student population. Most of them are non-science majors. As an educator and scientist, we have a mission to make contribution to educate our students at Indiana University with basic scientific and environmental literacy. Deep geological time is one key concept and a bottleneck in attaining scientific literacy.

4 The 4.6 billion-year history of Earth
Dinosaur extinction65 mya Note that the years in the table may be slightly different from other tables that you have seen or in your textbook. This is because over the years we still revise the dates. Radiometric dating of hardy minerals and meteorites, and moon rocks. The different periods are also marked with distinct fossil records. We are now in the Quaternary period, The 4.6 billion-year history of Earth

5 We are now in Holocene Epoch (11,500 years before present to the present)
Holocene is an interglacial period Pleistocene “most recent in Greek” (11, million years before present) Last glacial maximum 25,000 years ago

6 Review of Literature Preconceptions inhibit students from achieving an adequate understanding of DGT Numerical difficulties: Millions vs. billions (Trend 2000) Dinosaurs died before life began (Libarkin 2007) Confusion about basic science Lunar phases (Schoon & Boone 1998) Reasons for seasonal change (DeLaughter & Stein 1998) Global warming is due to destruction of Ozone layer Beyond IUB, across board questions. Not only related to my teaching. Not only related to IUB students. DeLaughter, J. E. and S. Stein (1998). "Preconceptions about earth science among students in an introductory course." EOS 79:

7 Review of Literature Elementary School
Ault, C. R. (1982). "Time in geological explanations as perceived by elementary school students." Journal of Geological Education 30: High School Hidalgo, A. J. and J. Otero (2004). "An analysis of the understanding of geological time by students at secondary and post-secondary level." International Journal of Science Education 26(7): Dodick, J. and N. Orion (2003). "Measuring student understanding of geological time." Science Education 87(5): College Libarkin, J. C., J. P. Kurdziel, et al. (2007). "College student conceptions of geological time and the disconnect between ordering and scale." Journal of Geoscience Education 55(5): Catley, K. M. and L. R. Novick (2009). "Digging deep: Exploring college students' knowledge of macroevoluntionary time." Journal of Research in Science Teaching 46(3):

8 Review of Literature – Suggested Learning Activities
Visualize magnitude by analogy or metaphor-based activities (Pyle 2007). Equate geologic time to physical distance (Richardson 2000, Hemler & Repine 2002) Translate DGT into a familiar time span (one calendar year) (Everitt, Good & Pankiewicz 1996, Nieto-Obregon 2001). Create personal metaphor (Ritger & Cummins 1991). All these activities presuppose that once students compare the geological time scale to a familiar distance, volume, mass or time period, they will be more likely to grasp the brevity of humans’ existence on Earth relative to the enormity of DGT.

9 Geologic Time Metaphors

10 Geologic Time Metaphors

11 Situational Factors Environmental Geology G171 for non-science majors
Possibly a gateway course 37 undergraduates in 2009 73% of students - First college science course 49% of students - Self reported knowing “almost nothing” about DGT Only 8% indicated being highly confident in their understanding of DGT Environmental geology: human interaction with our physical environment – planet earth.

12 Introductory Geology Courses
Earth Science: Materials and Processes Brophy/Dunning Fall/Spring G104 Evolution of the Earth Brassell/Millen G105 Earth, Our Habitable Planet Pratt/Douglas G111 Physical Geology Brophy Fall G112 Historical Geology Polly Spring G114 Dinosaurs and Their Relatives Johnson G116 Our Planet and Its Future Dunning G171 Environmental Geology Zhu/Douglas Similarly need DGT Similar student population A large number of students pass through these course. This is an important component of scientific literacy education on the campus

13 Why is DGT a bottleneck? Quantitative skills:
Large numbers, abstract numbers Proportions and scales Lack of scientific background and literacy Relation between geological time scale and something real (dinosaurs died a long, long time ago, 65 mya) My own experience

14 The Research Questions
Can participation in distance-metaphor building activities help students visualize the immensity of DGT? Does learning DGT help students acquire better scientific reasoning skills? To what extent does the case study method enable students to understand and apply the concept of DGT to problem-solving? *Students perceived the distance-metaphor activities as enabling them to visualize the immensity of DGT *Large increase in students’ confidence in their ability to engage in scientific reasoning using DGT *The majority of students demonstrated the ability to use DGT to engage in scientific reasoning *The majority of students applied the concept of DGT to problem-solve within case-study assignments

15 Decoding Discipline Model and the Freshman Learning Project
Background to Project Decoding Discipline Model and the Freshman Learning Project Where do most students get stuck? Pace, D and Middendorf, J Decoding the disciplines: Helping students learn disciplinary ways of thinking. New Directions for Teaching and Learning Summer, no. 98. Pace, D and Middendorf J Easing entry into the Scholarship of Teaching and Learning through focused assessments: The decoding the disciplines approach. In To Improve Academy, (Bolton: Anker Publishing).

16 How this study is different
Innovation: (a) a real world environmental problem with the need of understanding geological time scale that students can relate to and engage with; (b) future vs. past; (c) apply/outcome driven Scaffold learning - based upon Anderson’s Revised Taxonomy of Educational Objectives Cognitive Process Understand > Apply > Analyze Learning Opportunities Readings 3 - Lectures Class activities 2 Labs Homework #2 Case-Study in final exam According to Anderson’ Revised Taxonomy of Educational Objectives, learning is a process of building upon what a student already knows. In the taxonomy - before a person can apply something they must first understand it, and before they can analyze the must be able to apply it correctly. Hence this course attempted to scaffold the learning by providing students the opportunity to progress to the higher cognitive tasks By asking them first to understand it, then apply it and then analyze it, as described in the chart. Anderson, Lorin W., David R. Krathwohl, and Benjamin Samuel Bloom. A Taxonomy for Learning, Teaching, and Assessing : A Revision of Bloom's Taxonomy of Educational Objectives. Abridged ed. New York: Longman 2001.

17 Geological Repository for High-level Nuclear Wastes
Las Vegas Nevada Test Site Nevada Geological Repository for High-level Nuclear Wastes Yucca Mountain

18 Into the realm of geological time scale
July 9, 2004, the U.S. Court of Appeals of the District of Columbia vacated Environmental Protection Agency’s 10,000-year period for compliance Now to 1 million years or “within the period of geologic stability”

19 In the next million years …
Toilet paper for future 1 million years? Yucca mountain project for one million years? What do you think how many years should the repository be safe?

20 All of these orbital changes influence the amount of sunlight hitting the Earth.
The recurrence of ice ages is roughly on 100,000 and 40,000 time scales Figure 12.7b, solar radiation in June at 65o N latitude. Milankovitch cycle, due to earth eccentricity, obliquity, precession. Milankovitch cycle

21 How this study is different
Personal engagement Nuclear waste example; requires society’s decision and has an outcome students may care about; Case Study: local coal burning power plant (part of the final exam); Lab requires students to create a visual product representing geological time and apply it to the nuclear waste and global warming problems; Authentic Assessment – Students are asked to do the “type of thinking” and tasks that the expert in that field would do. Wiggins, Grant P Educative assessment: Designing assessments to inform and improve student performance. San Francisco, Calif.: Jossey-Bass.

22 Lab – Part I Mark the following events on the toilet paper, each sheet = 20 million years Sheets Geological time Events 0.0005 10,000 Age of human 0.75 15,000,000 Formation of Himalayan Mountains 3.25 65,000,000 Dinosaurs became extinct 9.00 180,000,000 Early birds and mammals 14.00 280,000,000 Dinosaurs appear, final assembly of Pangaea 18.5 363,000,000 Early trees, formation of coal deposits 28.5 570,000,000 Beginning of Cambrian period, rise of multi-cellular animals 170 3,400,000,000 Earliest life-forms (single-celled bacterial) 190 3,800,000,000 Oldest known Earth rocks 230 4,600,000,000 Origin of Earth

23 Step # Time Events 1 ~ 781,000 BP last magnetic pole reversal 2 ~126,000 BP base of Eemian interglacial phase 3 ~100,000 BP Neanderthal man 4 50,000 BP First Homo sapiens 5 15,000 BP The last glacial maximum 6 13,000 BP Humans first inhabit North America 7 10,000 BP End of last Ice Age, Modern man 8 8,000 BP Founding of Jericho, the first known city 9 ~6000 BP Human written records 10 2,000 BP Roman domination of the world 11 500 BP European rediscovery of the Americas 12 ~ 450 BP scientific revolution 13 ~220 BP First President of United States 14 ~150 BP Industrial revolution began 15 ~ 40 BP Humans first explore the moon 16 Now 17 2 AP Congressional election, 2010 32 AP Known crude oil reserves are used up (these numbers are highly contested. This number comes from Wikipedia as of November 14, 2006) 72 AP Known natural gas reserves are used up (these numbers are highly contested. This number comes from Wikipedia as of November 14, 2006) ~96 AP Global warming effects set in and global mean temperature increase 2 -4 oC. Sea level rises 18 ~100 AP The birth of your 5th generation offspring. 252 AP Known coal reserves are used up (these numbers are highly contested. This number comes from Wikipedia as of November 14, 2006) 19 290 AP The 100th Olympic game 20 328 AP The 100th FIFA World Cup 21 ~ 4000 AP The 1000th President of the United States 22 ~4800 AP 5000th anniversary of the foundation of the United States 23 ~25,000 AP Your 1000th great grandchildren 24 ~50,000 AP Next ice age 25 1,000,000 AP Safety of the Yucca Mountain repository Lab – Part II Using the perforations between sheets as a ruler, mark the names of items as listed in the table below. You will have to calculate the number of sheets required to complete each step in the table below. Each sheet of the paper towel is equal to 10,000 years

24 Follow up Homework Given your knowledge of the geological time scale and human history, what seems like a reasonable and feasible time period for the nuclear waste to be stored safely at the Yucca Mountain geological repository? Would 10,000 years be enough? 100,000 years? 1,000,000 years? Why? Be sure to support your answer by using geological numbers and the time scale of events that you identified in the lab. This answer should be about 4-5 sentences long.

25 Follow-up Homework Write an essay in which you either agree or disagree with the following statement: “We are in the warm period of the glacial and inter-glacial cycle, and are surely heading toward the next glacial period. Therefore, global warming is a good thing because it will delay the coming of the next ice age.”

26 Class Activities Pre-course knowledge survey at first class
Lectures and class discussion about DGT Distance-metaphor building lab Post lab survey/homework/essay Post-course knowledge survey at last class Final take home exam using case study method Pre-course knowledge survey given at first class Lectures and class discussion about DGT in preparation for lab Conduct distance-metaphor building lab Post lab survey Pre-course knowledge survey given at last class Final take home exam using case study method

27 Evidence of Student Learning
Pre and Post-Knowledge Survey Post lab survey Final Exam – Case Study

28 Knowledge Survey Measure students’ perceptions of their ability to solve problems, not their actual ability. Nuhfer and Knipp (2003) found that very few students display gross overconfidence when self reporting. They concluded that such “aberrations contributed by occasional individuals never affect a class average in a significant way” (p. 66). We averaged student scores to draw conclusions about improved DGT understanding and application. In their study on the validity of pre/post knowledge surveys, Nuhfer and Knipp (2003) found that very few students display gross overconfidence when self reporting. They concluded that such “aberrations contributed by occasional individuals never affect a class average in a significant way” (p. 66). Thus, we averaged student scores to draw conclusions about their improved understanding and application of DGT. Nuhfer, E. and D. Knipp (2003). "The Knowledge Survey: A Tool for All Reasons." To Improve the Academy 21:

29 Knowledge Survey Selected Questions
Explain the Geological Time Scale & why it is important to Environmental Geology Describe the age of the earth in geological time and how we know it is an accurate estimation Estimate the number of years we should guarantee buried high level nuclear waste will be safe at Yucca Mountain. Explain why. Estimate how far back we need to look into the geological past to determine if human activity is causing climate change. Describe why this is significant. Scale: How confident are you that you could answer this question on a graded test: 1 – Not confident 3 – Somewhat confident 5 – Very confident

30 Pre and Post-Knowledge Survey Results
Survey Test Question Pre-survey Post-survey Change Explain the Geological Time Scale and why it is important to Environmental Geology 2.27 4.26 1.99 Explain the time frame for determining the possible adverse effects of global warming (tens, hundreds, thousands, millions of years) 2.38 4.39 2.01 Describe the time frame for the cycle of glacial and interglacial periods (approximately tens, hundreds, thousands, millions of years) 1.86 3.91 2.05 Identify the Milankovich cycles and explain why they are important to Environmental Geology 1.19 3.87 2.68 Describe the age of the earth in geological time and how we know it is an accurate estimation 2.62 4.22 1.60 Identify how far back we need to look into the geological past to determine if human activity is causing climate change. Explain why this is significant. 4.00 1.62 Explain how scientists predict the future safety of nuclear waste disposal and what factors they must consider 2.19 3.78 1.59 Total Average Score 2.13 4.06 1.93 All positive changes Big jump in #4 Large increase in students’ confidence in their ability to engage in scientific reasoning using DGT

31 Post Lab Survey The lab helped me understand Geological Time
Strongly Disagree Agree Strongly Agree The lab helped me understand Geological Time 1 2 3 4 5 The lab helped me visualize the immensity of the Geological Time Scale The lab helped me relate geological time to current real world issues and the search for solutions The lab helped me answer the homework question about burying nuclear waste at Yucca mountain The lab helped me answer the homework question about human activity and global warming The lab help me understand the time frame for the cycle of glacial and interglacial periods The lab helped me see the relationship between the current geological era we are living in and the Geological Time Scale

32 Post Lab Survey Results
Ratings: 1 = strongly disagree 5 = strongly agree

33 Case Study You just joined a student environmental group. Write the text of a presentation you will give to IU student government defending the belief that anthropogenic activities are a contributor to global warming, and hence an important reason why IU should retire its coal fired power plant. Your presentation should: Explain the immensity of geological time, variations in CO2 concentrations and glacial & inter-glacial cycles within the Quaternary Use scientific reasoning (observations, theory, experiments, evidence & facts) to show that the CO2 increase is likely beyond natural variability Use graphs to support your argument Identify 2 other contemporary environmental issues which require an understanding of the geological time scale. Explain how.

34 Case Study Rubric Criteria Description of the immensity of DGT
Use of DGT to describe the link between the CO2 rise & global warming to human activity Use of DGT to argue that global warming won't inhibit next ice age Explanation of how DGT is key to understanding other environmental issues (excluding global warming) Scores 3 – accurate answer, clear & detailed 2 – accurate answer, some detail 1 – vague/unclear/answer indicated misunderstanding The ability to accurately describe the immensity of DGT The ability to link the CO2 rise/global warming to human activity, using DGT as part of argument The ability to argue that global warming won't inhibit the next ice age using DGT as evidence The ability to explain the importance of DGT to understanding other environmental issues (excluding global warming)

35 Case Study Results 65% Met 1 or more criteria, demonstrating at least a basic understanding of DGT 56% Demonstrated the ability to use scientific reasoning 45% Met 2 or more criteria, demonstrating a solid understanding of DGT 17.5% Met all 4 criteria, demonstrating an excellent understanding of DGT 7.5% Met and exceeded all 4 criteria, demonstrating an exceptional understanding of DGT Excellent Understanding of DGT: 3 students (7.5% of total) These students met and exceeded the 4 criteria. For example, they not only explained how DGT proves that the CO rise is related to human activity, they went into considerable depth about this. They also went into depth about why DGT is important to understanding other environmental issues. Good understanding of DGT: 4 students (10% of total) These students met all 4 criteria but explained the link to DGT in less depth than those who received a score of ‘excellent.’ OK (sufficient) understanding of DGT: 11 students (27.5% of total) These students met 2 or 3 out of the 4 criteria and they went into enough depth that it was clear that they understood the concept of deep geological time. Poor-ok understanding of DGT: 8 students (20% of total) These students met 1 or 2 out of the 4 criteria but they didn’t go into enough depth to make it clear that they understood the concept of DGT. Nor was I sure they didn’t understand it. They we too vague for me to know whether or not they understood DGT. Poor (or nonexistent) understanding of DGT: 14 students (35% of total) This group includes students who didn’t meet any of the criteria. This includes 3 students who didn’t mention DGT at all in their essays. This group also includes students who met only one of the 4 criteria well. This group also includes students who met 1 or 2 of the criteria in a weak or very underdeveloped way. The students in this group either didn’t understand DGT at all, didn’t read the directions for the essay or didn’t put effort into fulfilling the stated requirements for the essay. 45% of students demonstrated in their final exam essay that they had an adequate (or solid) understanding of DGT. (This is the three top categories combined.)

36 Conclusions Students perceived the distance-metaphor activities as enabling them to visualize the immensity of DGT Large increase in students’ confidence in their ability to engage in scientific reasoning using DGT The majority of students demonstrated the ability to use DGT to engage in scientific reasoning The majority of students applied the concept of DGT to problem-solve within case-study assignments These conclusions are especially striking given: Weak science background of most students 49% reported no knowledge of geology 73% first undergraduate science course Research Questions Can participation in distance-metaphor building activities help students visualize the immensity of DGT? Does learning DGT help students acquire better scientific reasoning skills? To what extent does the case study method enable students to understand and apply the concept of DGT to problem solving?

37 Next Steps Adjustments to the course
This Fall we added an additional metaphor building activity to the lab, asking students to create their own visual depiction of the immensity of DGT, after they have worked in teams using the toilet paper exercise to visualize its immensity. Further Research Larger sample size Examine students’ ability to transfer problem solving skills to a different discipline, course, or problem set 8 courses involving DGT – so potentially large consequences.

38 Thank you In conclusion: weathering rates in the field are strongly coupled with secondary mineral precipitation rates. Weathering reaction or the dissolution of the primary minerals occurs in the context of a geochemical reaction network. Considering this network reconciles part of the apparent discrepancy. As I mentioned in the introduction, feldspars are the most abundant minerals in the earth crust. Their weathering rates are central to many environmental and geological processes. Reconciliation of even part of the apparent discrepancy will help to quantitatively predict many geological and environmental processes, such as weathering, nuclear waste disposal, and geological carbon sequestration. Thank you

39 Case Study Results 65% Met 1 or more criteria, demonstrating at least a basic understanding of DGT 45% Met 2 or more criteria, demonstrating a solid understanding of DGT 17.5% Met all 4 criteria, demonstrating an excellent understanding of DGT 7.5% Met and exceeded all 4 criteria, demonstrating an exceptional understanding of DGT 56% Demonstrated the ability to use scientific reasoning Excellent Understanding of DGT: 3 students (7.5% of total) These students met and exceeded the 4 criteria. For example, they not only explained how DGT proves that the CO rise is related to human activity, they went into considerable depth about this. They also went into depth about why DGT is important to understanding other environmental issues. Good understanding of DGT: 4 students (10% of total) These students met all 4 criteria but explained the link to DGT in less depth than those who received a score of ‘excellent.’ OK (sufficient) understanding of DGT: 11 students (27.5% of total) These students met 2 or 3 out of the 4 criteria and they went into enough depth that it was clear that they understood the concept of deep geological time. Poor-ok understanding of DGT: 8 students (20% of total) These students met 1 or 2 out of the 4 criteria but they didn’t go into enough depth to make it clear that they understood the concept of DGT. Nor was I sure they didn’t understand it. They we too vague for me to know whether or not they understood DGT. Poor (or nonexistent) understanding of DGT: 14 students (35% of total) This group includes students who didn’t meet any of the criteria. This includes 3 students who didn’t mention DGT at all in their essays. This group also includes students who met only one of the 4 criteria well. This group also includes students who met 1 or 2 of the criteria in a weak or very underdeveloped way. The students in this group either didn’t understand DGT at all, didn’t read the directions for the essay or didn’t put effort into fulfilling the stated requirements for the essay. 45% of students demonstrated in their final exam essay that they had an adequate (or solid) understanding of DGT. (This is the three top categories combined.)

40 Sources Ault, C. R. (1982). "Time in geological explanations as perceived by elementary school students." Journal of Geological Education 30: Catley, K. M. and L. R. Novick (2009). "Digging deep: Exploring college students' knowledge of macroevoluntionary time." Journal of Research in Science Teaching 46(3): DeLaughter, J. E. and S. Stein (1998). "Preconceptions about earth science among students in an introductory course." EOS 79: Dodick, J. and N. Orion (2003). "Measuring student understanding of geological time." Science Education 87(5): Everitt, C. L., S. C. Good, P. R. Pankiewicz (1996). "Conceptualizing the inconceivable by depicting the magnitude of geological time with a yearly planning calendar." Journal of Geoscience Education 44: Fink, L. Dee (2003). Creating significant learning experiences: An integrated approach to designing college courses. San Francisco, Calif.: Jossey-Bass. Hawkins, D. (1978). "Critical barriers to science learning." Outlook 29: 3-23. Hemler, D. and T. Repine (2002). "Reconstructing the geologic timeline." The Science Teacher 69(4): Hidalgo, A. J. and J. Otero (2004). "An analysis of the understanding of geological time by students at secondary and post-secondary level." International Journal of Science Education 26(7):

41 Sources Libarkin, J. C., J. P. Kurdziel, et al. (2007). "College student conceptions of geological time and the disconnect between ordering and scale." Journal of Geoscience Education 55(5): Nieto-Obregon, J. (2001). "Geologic time scales, maps, and the chronoscalimeter." Journal of Geoscience Education 49(1): Novak, J. D. (1988). "Learning science and the science of learning." Studies in Science Education 15: Nuhfer, E. and D. Knipp (2003). "The Knowledge Survey: A Tool for All Reasons." To Improve the Academy 21: Pace, D and J Middendorf (2004). Decoding the disciplines: Helping students learn disciplinary ways of thinking. New Directions for Teaching and Learning Summer, no. 98. Pyle, C. (2007). "Teaching the time: Physical geography in four dimensions." Teaching Geography 32(3): Richardson, R. M. (2000). "Geologic time (clothes) line." Journal of Geoscience Education 48: 584. Ritger, S. D. and R. H. Cummins (1991). "Using student-created metaphors to comprehend geologic time." Journal of Geological Education 39: 9-11. Schoon, K. J. (1992). "Students' alternative conceptions of Earth and space." Journal of Geological Education 40: Schoon, K. J. and W. J. Boone (1998). "Self-efficacy and alternative conceptions of science preservice elementary teachers." Science Education 82(5): Trend, R. D. (2000). "Conceptions of geological time among primary teacher trainees, with reference to their engagement with geoscience, history, and science." International Journal of Science Education 22(5): Wiggins, Grant P. (1998). Educative assessment: Designing assessments to inform and improve student performance. San Francisco, Calif.: Jossey-Bass

42 Atmospheric CO2 in the past
Geological time scale and geological history play two important things: first natural variability. CO2 concentrations did vary, but the human activity anomaly is difficult to refute. Ground truth for modeling to predict future.

43 Yucca Mt. – Potential Repository
Desert climate (170 mm/yr vs. Bloomington ~1200 mm/yr); On federal land; Away from large population centers; Nevada has only two congress men (and two senators); 30 years study and 30 billion dollars.

44 Infiltration rate At present, evaporation exceeds precipitation (170 mm/yr) - hypothesis; Water drips down in tunnel – reality check; When is the next ice age?

45 Estimated Recharge for Yucca Mountain
(Zhu et al. Water Resources Research , 2003) 15±5 mm/yr 5±1 mm/yr With this information, we can use the CMB method to estimate recharge rates The resulting recharge calculated for the Holocene is 5 mm/yr and the Pleistocene was 15 mm/yr. NEXT SLIDE U.S. Nuclear Regulatory Commission: Next 10 ky mm/yr 10 ky - 1 ma


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