Identifying Conceptual Barriers in College Students' Understanding of Rock Formation, Summaries of Geology

Download Identifying Conceptual Barriers in College Students' Understanding of Rock Formation and more Summaries Geology in PDF only on Docsity! Research: Kortz and Murray - Barriers to Learning Rocks Barriers to College Students Learning How Rocks Form INTRODUCTION Rocks and how they form are among the fundamental topics in geology because we need to understand them in order to understand Earth’s history and processes. The three rock types and the rock cycle are essential topics students should learn in college-level introductory geoscience classes (Kelso et al., 2000). Although rocks are a key element in most introductory classes in lectures, labs, and/or field trips, there is scant research on college students’ conceptions (or alternative conceptions) of rock formation (Kusnick, 2002; Kortz, 2009). To being able to effectively teach students scientific material, it is important to know if they are entering the classroom with alternative conceptions and what those alternative conceptions are. Students are not blank slates, and they use their prior knowledge to construct ideas about the Earth (e.g. Chang and Barufaldi, 1999; Kusnick, 2002; Taber, 2003). Although this prior knowledge may be non-scientific, students may still use it as a base for new knowledge taught in the classroom. As a result, they construct an inappropriate mental model, or representation of the phenomena. Therefore, students cannot learn the scientific perspective if they have their alternative conceptions still in place (e.g. Committee on Undergraduate Science Education, 1997; Clement, 2000; Gobert, 2000; National Resource Council, 2000; Taber, 2003; Chi, 2008). By knowing what those potentially non- scientific ideas are, instructors, researchers, and curriculum developers are better able to achieve an understanding of students’ learning difficulties and help them appropriately. Previous research on students’ conceptions of rocks has focused mostly on children and how they describe and classify rocks (e.g. Happs, 1982; Blake, 2001; Blake, 2004; Blake, 2005; Ford, 2005; Dal 2006). However, Kusnick (2002) investigated pre-service elementary school teachers on their conceptions of rock formation based on writing assignments the students completed during the semester. She described many common alternative conceptions of those students and noted deeply-held beliefs of students that lead to those alternative conceptions. Similarly, Kortz (2009) found that college students in introductory geology classes do not view rocks as part of processes but instead as individual objects that often do not change. Notably, because many students view rocks as static objects, they may not intuitively understand that rocks form and change over time. Moreover, students often mix up the three rock types and do not discriminate between the distinct formation processes that distinguish them (Kortz, 2009). Several investigators have examined in greater depth the underlying factors behind many of the alternative conceptions students have science in general, and about rocks in particular. We present a synopsis of their work as it pertains to the difficulties students have in understanding the rock cycle, that is organized around the terminology those investigators have introduced into the geoscience literature. Critical Barriers – Hawkins (1978) identified “critical barriers” that prevent students from fully understanding scientific phenomena, and Ault (1984) applied them to rock formation. They define a critical barrier as “exceedingly unobvious” ideas that are difficult to overcome, since patient explanation rarely immediately cures it (Hawkins, 1978; Ault, 1984). Although grasping critical barriers is necessary to understanding in a discipline, they are often mastered relatively late in the learning of a science, despite their “elementary” nature. They often result from the conflict between common sense, intuitive, everyday notions about phenomena and the structure of scientific thoughts. Critical barriers are typically fundamental or basic concepts in a discipline, with the intimation that they should be easy to grasp. To the contrary, they are usually complex and subtle ideas, which are the end product of years of scientific research and controversy. They also presume significant prior knowledge about the topic, a point that becomes immediately evident when you attempt to “unwrap” a critical barrier. This occurs when developing STEM curricula that address grade span expectations (i.e., Karen M. Kortz1, Daniel P. Murray2 1Physics Department, Community College of Rhode Island, 1762 Louisquisset Pike, Lincoln, RI 02865; kkortz@ccri.edu 2CELS – Department of Geosciences, University of Rhode Island, Woodward Hall, Kingston, RI 02881; dpmurray@uri.edu ABSTRACT Students do not have a good understanding of how rocks form. Instead, they have many non-scientific alternative conceptions to explain different aspects of rock formation. Using 10 interviews and nearly 200 questionnaires filled out by students at four different colleges, we identified many alternative conceptions students have about rock formation. We then used themes within those alternative conceptions to identify the underlying conceptual barriers that cause them. Conceptual barriers are deeply-held conceptions that prevent students from understanding scientific explanations. One conceptual barrier can cause many alternative conceptions, and alternative conceptions can be the result of more than one conceptual barrier. The seven conceptual barriers identified in the study that prevent students from understanding rock formation are Deep Time, Changing Earth, Large Spatial Scale, Bedrock, Materials, Atomic Scale, and Pressure. Because of these conceptual barriers, students cannot form scientifically correct mental models of how rocks form, resulting in alternative conceptions, so the conceptual barriers need to be overcome before students truly learn the scientific explanations of how rocks form. The results of this study can be applied to other areas of geology in addition to rock formation. 301 Journal of Geoscience Education, v. 57, n. 4, September, 2009, p. 300-315 standards) for K-12, as they often unwittingly list critical barriers as standards. Examples of specific critical barriers we have encountered in geoscience courses include the rock cycle, strike and dip, cladograms, and earthquake prediction. Of relevance to this paper is the classification of Ault (1982, 1984). He identified four broadly defined barriers to understanding the formation of rocks: 1. Bedrock – its existence, its scale, the pattern of layering, and other inferences about unobserved events 2. Large-scale physical patterns and the physical changes they represent 3. Geologic time 4. Scale (spatial) Conceptual Prisms – Although the concept of critical barriers gives us a convenient framework for describing and categorizing ideas that students find difficult to grasp, it provides little insight into the reasons why these barriers occur. The work of Kusnick (2002) is germane, as she demonstrated that students have deeply held beliefs about the world, termed “conceptual prisms,” that distort their understanding of how rocks form. Conceptual prisms result from the interaction of the student’s world view and personal experience with what they were taught about rocks. They are deeply held but largely unexamined beliefs that refract geologic instruction, resulting in a spectrum of ideas about geology. The four conceptual prisms suggested by Kusnick are: 1. What is a rock? (common language vs. scientific language) 2. Scales of space and time 3. Stable Earth (landscapes are forever) 4. Human dominance (humans play a role in rock formation) Clearly Ault’s critical barriers to understanding rocks share much in common with Kusnick’s conceptual prisms. However, the latter classification attempts to identify a deeper and more general set of barriers to learning that apply not only to understanding the rock cycle, but also to many other scientific ideas. This issue is the subject of an extensive literature that addresses the reasons why humans find seemingly “simple” scientific and mathematical concepts so difficult to grasp. It draws heavily from cognitive science and evolutionary psychology, and implies that there are universal constraints on how we process information, and that these constraints are “hard-wired”. A review of this work is beyond the scope of this paper, and the reader is referred to Pinker (1997) and Marcus (2008) for entrées to the literature. Threshold Concepts – Most recently, “threshold concepts” have been invoked to explain difficulties that students have in learning many topics over a wide range of disciplines (Meyer and Land, 2003; Stokes et al., 2007). Threshold concepts are a “mental blockage” that when cleared results in understanding or ‘insight’ opening up a whole new way of thinking or practicing in a discipline. They represent a transformed way of understanding, something without which the learner finds difficult to progress within the curriculum. Although little research has been performed to identify threshold concepts in geology, an extensive list was created of possible threshold concepts at a workshop on threshold concepts in geography, earth, and environmental sciences (Geography, Earth and Environmental Sciences Subject Centre (GEES), 2006). The workshop participants (GEES, 2006) and other researchers (e.g. Truscott et al., 2006) include the following possible threshold concepts relating to rocks and their formation: 1. Time - deep/geological time, absolute time 2. Scale e.g. time, distance, space 3. Rates of activity 4. Metamorphic processes 5. Crystallography 6. Chemical reactions 7. Bonding interactions of atoms 8. Rock cycle 9. Tectonic plate The “mental blockage” of Meyer and Land is the same as Ault’s critical barrier. However, unlike Ault, Meyer and Land are focused on the transformative process by which the barrier is removed. Conceptual Barriers – In this study, we identify common alternative conceptions of college students’ understanding of rocks and their formation. Our goal is to use patterns in these alternative conceptions to find their underlying conceptual causes which pose barriers to students’ comprehension. As Libarkin and others wrote (2003), “Understanding the common thought processes applied to different content matter is a powerful method for understanding how students view the world around them.” The findings of previous studies regarding barriers to learning are used as an initial platform to aid in our investigation of the underlying conceptual causes. Although they are not completely analogous, critical barriers, conceptual prisms, and threshold concepts all are concerned with the barriers to learning, and the ways in which they may eliminated. We will use the term conceptual barrier in this paper to describe this idea. As used in this paper, a conceptual barrier is an underlying, deeply held conception that prevents students from understanding the scientific explanation. Here, the term also refers to the underlying causes of the barrier, and the ways in which they can be eliminated. METHODS Methodological Approach – We used a qualitative approach to identify alternative conceptions of students and analyze them for underlying conceptual barriers. Specifically, we relied on in-depth interviews of students’ views of rocks and their formation and questionnaires about rocks and interpretations made from rocks. We chose a qualitative approach in order to gather rich Research: Kortz and Murray - Barriers to Learning Rocks threshold concepts (GEES, 2006), were used to help create these overarching themes. We established four initial themes from the initial analysis of the questionnaires. These themes were: rocks = handsamples not bedrock; scales of space (atomic to kilometers) and time; stable Earth; and recycling of materials. We interpreted the alternative conception described in the example above, “Igneous rocks are not the result of magma crystallizing,” to be a result of the students not understanding the atomic processes involved with magma crystallizing into minerals forming a solid rock, so it could be explained by the “scales of space and time” overarching theme. Once the initial overarching themes were established from the questionnaires, the interviews were analyzed with those themes. During the interviews, the students explained their thoughts in much greater detail than on the questionnaire and gave explanations of their thinking resulting in some of the alternative conceptions. With this additional information, we adjusted and refined the themes using the constant comparative method to best reflect the thinking of the students. For example, we found that the initial theme combining the scales of a range of distances and time was too heterogeneous to properly reflect students’ thoughts and difficulties with understanding geologic concepts, so we divided it into the separate categories of microscopic distances, immense distances, and long periods of time. Finally, the student answers on all questions on the questionnaires were analyzed with the newly adjusted themes, to reclassify the alternative conceptions and verify that the themes truly represent the student data. At this point, no major changes were made to the themes, and we felt satisfied that we had captured the essence of the conceptual barriers to students’ understanding with our themes. We discussed the themes with colleagues to get additional perspectives. Building Trustworthiness – Trustworthiness in qualitative research is what validity and reliability are in quantitative research. Erlandson and others (1993) wrote (based on the paradigm established by Guba and Lincoln, e.g. Lincoln and Guba, 1985) that trustworthiness “demonstrate[s] its truth value, provide[s] basis for applying it, and allow[s] for external judgments to be made about the consistency of its procedures and the neutrality of its findings or decisions” (page 29). The four aspects of trustworthiness are credibility, transferability, dependability, and confirmability. Each of these, as it applies to this study, is described in Table 2. Study Limitations – In this study, there were ten students who were interviewed, all from the same East Coast community college, and they were purposefully selected to get the most information from the interviews. Because these students were not randomly selected, we cannot say they are a representative sample of the overall population of geology students, even at the one community college. Although nearly 200 students filled out the questionnaires, from a diversity of institutions across the United States, the questionnaires did not probe students’ beliefs so they represent a minimum of alternative conceptions. As a result, although the themes identified describe the students in our population with a high rate of consistency, they may not be fully representative of the overall population of geology students. Further research is needed to determine how widespread and deeply held the barriers are across populations. CONCEPTUAL BARRIERS TO LEARNING Many of the alternative conceptions that students have will still give them correct answers on many questions about rock formation. Therefore, it is often difficult to know if the students truly understand the processes that form rocks. Table 3 lists quotes from students during interviews that give the impression that TABLE 2. TRUSTWORTHINESS AND HOW IT IS APPROACHED IN THIS STUDY Aspect of Trustworthiness What It Measures Comparison to Quantitative Research How It Is Approached in This Study Credibility (whether the research conclusions match what the participants thought) Truth Value Internal Validity • Triangulation (collection of information from different points of view) with interviews and questionnaires • Triangulation with questions on different topics to collect student views from different perspectives • Interviewer summarized student descriptions back to students • Colleagues provided feedback after reading portions of interviews • Use of student quotes to demonstrate link between students’ words and interpretations Transferability (the extent the findings can be applied outside of the study) Applicability External Validity • Description of classes and students from which data were collected • Purposive sampling to maximize the range of information from the interviews Dependability (whether the findings would be repeated under similar conditions) Consistency Reliability • Triangulation (described above) • Code-recode procedure of analysis • Peer review by colleagues Confirmability (whether conclusions can be tracked to the source) Neutrality Objectivity • Triangulation (described above) • Student quotes used to illustrate link between source and interpretations 305 Journal of Geoscience Education, v. 57, n. 4, September, 2009, p. 300-315 they understand the rock forming process. However, upon further probing during the interviews, the students reveal some alternative conceptions (also given in Table 3), indicating that the students do not truly understand how the rocks formed. The alternative conceptions illustrated in Table 3 are a just a few examples of the vast array of alternative conceptions students possess about rocks and their formation. In the following section, we explain our theory that many of these alternative conceptions exist because there are underlying conceptual barriers to student learning. Because students do not have a good understanding of these underlying conceptual barriers, they cannot have an accurate picture of how rocks form, resulting in alternative conceptions. Table 4 summarizes the seven conceptual barriers to learning how rocks form that were identified in this study as well as alternative conceptions that result from the conceptual barriers. These conceptual barriers are described in detail below. Example alternative conceptions that are caused by each barrier are also described, as well as some possible explanations that these beliefs exist. The frequency with which the students displayed the conceptual barriers and alternative conceptions in the interviews and questionnaires is also given in Table 4. The alternative conceptions listed are selected because they were expressed by at least three students in this study. In addition, some of the alternative conceptions were previously described by other researchers as well, and we note where this is the case. Many of the students’ alternative conceptions are related to more than one barrier. For example, this study found that the idea that granite forms from magma is an extremely difficult concept for students to grasp because there are many conceptual barriers that need to be overcome to succeed in learning this concept. As a result, students have many alternative conceptions to explain the formation of granite. Deep Time – Because most geological processes take a very long time to happen, students need to have a grasp of the concept of geologic time to truly understand how rocks form. In order to make sense of the rock cycle, students also need to realize that it takes many millions of years for rocks to cycle through. However, students do not have a good grasp of deep time (Trend, 2000; Trend, 2001a; Trend, 2001b; Dodick and Orion, 2003a; Dodick and Orion, 2003b; Hidalgo and Otero, 2004; Libarkin et al., 2007) and try to put the formation of rocks into scales with which they are familiar. Examples of alternative conceptions that are caused by this conceptual barrier are: 1. A “long time” is at most thousands of years. When students hear that rocks take a “long time” to form, they think in terms of their own lives, and most place the time scale to be hundreds to thousands of years. This time scale makes it impossible for students to understand slow processes such as metamorphism or the formation of thick layers of sedimentary rock. For example, when David was asked how long it took for a rock to change to the way it looks now, he responded, “It would take a great deal of time. It’s not something that just happens, maybe a couple TABLE 3. CORRECT-SOUNDING STUDENT QUOTES UNTIL THEY ARE EXPLAINED It Sounds Good (Student Quote) But…(Further Explanation by Student) Andrew: “The lava comes up through hotspots and it forms basalt when it cools.” Basalt is made from sediments. Sediments form in the core, are brought to the surface by hotspots, then mold together to form the rock basalt. James: “This is the extrusive rock… Extruded from some kind of volcano.” The rock came from the magma chamber wall or the volcano. It came out of the volcano, possibly carried by the magma, but it can not stay in the magma because it would melt. Elizabeth: “Maybe if the magma was still inside of the Earth and it didn’t come up, parts of that magma could become granite.” Basalt picks up crystals from a rock layer as it rises to the surface. Under pressure beneath the surface, the crystals combine to get bigger and form granite. Carlos: “But when that rock [granite] starts cooling down, … the formation stops.” In beach sand, minerals pack together, and the compression is from volcanic heat or hot weather. The rocks become bigger over time, but stop growing when the compression from heat stops. James: “This rock [granite] probably formed in some underground magma chamber that cooled.” Minerals are added to magma from the chamber walls or from other rocks in the magma. The minerals migrate to each other, fuse, and cool slowly to form rock. Andrew: “One of those softer rocks like silt or shale… can be formed by the different sediments that are like, almost like mud or something that it will come together.” Streams carry sediments, which then clump together. The clumps are deposited at the sides or end of the river, and they dry to form rocks. The drier the rock gets, the weaker it gets. Elizabeth: “[Sand] would somehow need to get deposited into the earth. … It becomes layered, so the deepest layers gets the most heat and pressure and becomes sandstone.” The layers are several centimeters thick, so the rock is forming less than a meter below the surface. Grace: “When … the limestone becomes – comes together and becomes a solid form, maybe it encaptures some of the life that was in the ocean.” Limestone is sticky and soft, attracting shells to it. It slowly hardens over time because it dries and the calcium in it hardens. David: “Metamorphic is like changing rock, I believe. It changes over time.” Metamorphism includes weathering of the rock’s surface and imprints from fossils. Elizabeth: “I think it was broken off of a bigger piece… It would be a layer of the Earth.” The layers of the Earth about a meter long and several centimeters thick. Research: Kortz and Murray - Barriers to Learning Rocks hundred years.” 2. People play a role in moving sediments and rocks. People are naturally anthrocentric, so they place humans into roles of moving ancient sediments and rocks (Kusnick, 2002). This belief likely stems from students’ personal experience of the human influence in city landscapes, such as seeing excavations and noticing sediments on roads. In addition, some students may have heard humans are currently Earth’s principal geomorphic agent (e.g. Hooke, 2000 and Wilkinson, 2005), but did not consider the different time scales involved between human activities and the formation and deformation of rocks. Students also describe animals, usually birds and fish, as often playing a role in moving sediments and rocks. For example, Harriet described fossils in a sedimentary rock as forming because “the fish dropped the empty shells down and then another deposit of the ocean floor bed came over, you know, just by, like, currents or whatever moving the ocean floor around depositing more clay on top of the shells and then more little fish drop more shells.” Students do not picture enough time to be able to see significant changes from slow geologic processes. 3. Rocks come to the surface through volcanoes or earthquakes. Because students cannot picture the wearing away of thick layers of rock, they describe a much quicker process of bringing deeply-formed rocks to the surface where we can see them. These catastrophic events quickly move rocks to the surface. Changing Earth – Students view the Earth as static, so they do not think of things as forming. Because rocks form and are a result of changes to the Earth, this view inhibits students from truly understanding how rocks form (or that rocks form!) and what they can tell us about the Earth in the past. This barrier is tied to the Deep Time barrier, because if students do not understand the enormous lengths of time available for geological processes to act, they will not believe that things on Earth can change. David is an example of a student who does not have a complete grasp on the idea of a changing Earth, illustrated by the following quote: Int: If it [a rock] started off underground…, how did it n interview2 % questionnaire3 Deep Time1 A “long time” is at most thousands of years. People play a role in moving sediments and rock. Rocks come to the surface through volcanoes or earthquakes. 9 5 5 4 5% 0 1 2 Changing Earth Features on the Earth do not appear or disappear. Rocks pre-exist in magma. Sedimentary rocks are located in the environment in which they are formed. Igneous and metamorphic rocks need exotic conditions to form. 9 1 2 4 3 15 10 2 1 1 Large Spatial Scale Sedimentary rocks form at or just beneath the Earth’s surface. Layers in rocks are the same as layers in the Earth. Volcanism is needed to provide the heat for rock formation. Rocks move down into the Earth through earthquakes, divergent boundaries, cracks, or by burying themselves. Magma and rocks come from the core. 10 3 4 4 3 4 5 1 0 0 2 1 Bedrock A rock forms as a hand sample. Pieces purposely gather to form rocks. Granite is made from sediments. The ground is not made of rock. 9 7 4 5 2 22 16 1 2 4 Materials Magma turns into a black rock and black rocks were magma (i.e. black = igneous). Rocks can change color. Rocks can change into any other rock. 7 4 2 2 5 1 1 2 Atomic Scale Igneous rocks are not the result of magma crystallizing. Sedimentary rocks form by wet sediments drying. Minerals form separately, then come together to form rocks. Metamorphic rocks melt. 10 8 3 3 2 9 5 0 1 2 Pressure Pressure to form rocks is caused by things like heat, water, faults, and air. 7 6 1 1 1Critical barriers to learning (in bold) and example alternative conceptions that result 2n interview is the number of interviewed students (out of 10 students) expressing misconceptions explained by this barrier or expressing the given misconceptions 3% questionnaire is the percentage of students who completed questionnaires expressing misconceptions explained by this barrier or expressing the given misconceptions. TABLE 4. CRITICAL BARRIERS AND RESULTING ALTERNATIVE CONCEPTIONS 309 Journal of Geoscience Education, v. 57, n. 4, September, 2009, p. 300-315 different minerals of different colors, shapes, and sizes, students picture those minerals coming together to form granite as an accumulation of sediments. Some students described granite as sand accumulating and then compressing together. Students picture granite forming as a small rock that might form as large as a countertop (see previous student discussion under “A rock is a handsample”). Carlos describes a sedimentary process for forming granite in the following quote: “A lot of beaches, they have different color sand… You basically take… some of the black, some of the white, some of the mix that we have here, and you end up crush it together, you end up forming a new type of rock or a certain type of rock, like granite…. Maybe Connecticut might have certain type of granite, and maybe in like California they might have a different type of granite, because it’s a different area with different sediment coves.” 4. The ground is not made of rock. Students see mountains and volcanoes as being made out of particles, such as boulders, smaller rocks, and dirt, instead of solid rock. When asked what mountains are made of, Beth responded, “The actual particles that make up the mountains? Because that’s sand and some little rock pieces, like the big sand and gravel pieces.” Ault (1984) also identified this alternative conception. This view furthermore results in students not realizing that volcanoes are formed from the build-up of lava. Carlos describes a volcano being there before it started erupting lava, “It starts building up kind of like… a mountain and when the volcano starts to become active…” This alternative conception was also documented by Dal (2006), and relates to the conceptual barrier of Changing Earth. Materials – To know what a rock is and how it formed, you need to know the materials that make up that rock. Minerals and the elements that make them are key factors in rocks. Not understanding the relationship between rocks, sediments, minerals, and atoms poses large barriers to learning how rocks form. Examples of alternative conceptions that are caused by this conceptual barrier are: 1. Magma turns into a black rock and black rocks were magma (i.e. black equals igneous). If students see a black rock or black pieces in a rock, they automatically think igneous. On the flip side, when students think of igneous rocks, they picture the rock as black. This alternative conception results from the everyday experience of hot, burnt material being black. Also, when students see pictures of volcanoes erupting, the resulting rock is typically black. As a result, although students understand basalt is igneous, they cannot picture granite as being an igneous rock. Andrew describes a granite handsample, explaining that it could not have been magma, “I think it was solid rock because I think if it was lava it would be more just black, more solid black. It may have been partly lava because there is some black in here… But I think it was not originally lava because I think it would be a darker color than what it is.” 2. Rocks can change color. Although weathering may change the color on the surface of a rock, students believe that the color of the entire rock can change. One of the most common factors that students attribute to changing rock color is heat, which they feel can make a rock redder or black. Grace describes this perspective, “I would have thought that heat would have made it darker just because, kind of when you think about volcanic rock, it’s black and you kind of just associate blackness with heat.” Students who view that rocks can change color will have a difficult time understanding the information geologists gather from rock color, such as composition of igneous rocks and organic content in shale. 3. Rocks can change into any other rock. Because many students do not understand the chemical and mineral make-up of rocks, they picture that any rock can change into any other rock. For example, on the ques t ionnaire , s tud ents descr ibed gra ni te metamorphosing into marble, sandstone melting into granite, and basalt turning into limestone. Sibley and others (2007) also described students’ use of nonsensical transitions of rock types. Atomic Scale – The formation of most rocks results from atoms crystallizing into minerals. If students do not understand the very basics of atoms and especially the processes of how they react with each other, they will have a difficult time grasping the formation of rocks, especially igneous and metamorphic. Examples of alternative conceptions that are caused by this critical barrier are: 1. Igneous rocks are not the result of magma crystallizing. Students have a difficult time accepting that minerals grow from “nothing,” although they acknowledge that rocks can change and minerals in them can grow larger. Students cannot picture how a homogeneous liquid can turn into a heterogeneous solid, such as granite. An example of a student (Elizabeth) with this alternative conception is, “I don’t know what rock it would have been before granite. Because it would have to have at least some evidence of small crystals I would say.” Since many students view minerals as being added to the rock, or the rock originally starting with small crystals already in it, students view magma as allowing the minerals to combine and grow. They do not see the magma itself crystallizing. Therefore, the belief that magma does not crystallize results in some students thinking that lava does not turn into a rock. For example, one student answered on Questionnaire 7E that “Basalt is found near lava/magma,” illustrating that basalt and lava are separate entities. 2. Sedimentary rocks form by wet sediments drying. Students have seen mud (a sediment) or cement dry to form a solid mass, and translate this process to the formation of sedimentary rocks without considering the differences between sediments and rocks at the atomic level. This alternative conception (observed as well by Research: Kortz and Murray - Barriers to Learning Rocks Kusnick, 2002) also ties to students not understanding the immense time scales involved in forming rocks. This belief may also be enforced by students learning that many sedimentary rocks form in the absence of water, such as limestone forming when oceans evaporate, sandstone forming from dry desert sand, and conglomerate forming after flooding. As a corollary, students believe that sediments in a sedimentary rock are held together by dried mud, something cement-like (in the sense of concrete), or something sticky. Students do not view the sediments as being attached at the atomic level. 3. Minerals form separately, then come together to form rocks. Students do not always describe a rock forming in place. They often describe minerals forming in one place, and then being transported to form a rock. Andrew expresses this perspective when talking about granite, a rock with obvious minerals, “They [sediments] form together from coming up to the surface of the Earth and then they come to the top of the crust to form, they basically cool together to form different parts of the rock.” Notice that this student correctly describes granite as forming when minerals cool, although he has a very different process pictured than geologists do. This view of minerals forming separately from rocks leads to students having difficulties distinguishing how the three different rock types form, since this view would have all rocks forming in the same general way. 4. Metamorphic rocks melt. Students do not understand the atomic changes involved in metamorphosing rocks. Because metamorphism is often described as involving heat and pressure, students often assume that the heat means the rocks melt. They have little experience with things changing in the solid state, so they cannot picture it happening. Pressure – Most rocks, as they are changing or forming, are compressed by immense pressures. These pressures are outside the normal experiences of students, and are therefore difficult to grasp and understand their cause. An example of an alternative conception that is caused by this conceptual barrier is: 1. Pressure to form rocks is caused by things like heat, water, faults, and air. Although students realize that most rocks require pressure to form, they do not have a firm grasp of what causes pressure. Because many rocks require both heat and pressure to form, many students link the two in a causal relationship, with heat causing the pressure. Also, many students underestimate the amount of pressure necessary to compress sediments together and think that air and water (such as at the bottom of a stream) could cause enough pressure. Carlos describes several causes of pressure for the formation of granite in the following quote: “I believe it needs water because it needs to get basically compressed together. You can do it by heat, like volcanoes do if they melt. You can do it by water, cause if you take sand and put it together, and say you leave it there in a hot, hot place, it’ll get harder and harder, and all the different things that are in there basically it’ll decrease the water in the sediment, and it’ll get all compressed together by the weather again.” DISCUSSION Pervasiveness of Conceptual Barriers – The conceptual barriers are widespread among students. All ten of the interviewed students held alternative conceptions that can be explained by the seven conceptual barriers. One student (Felipe) was identified as having only three of the seven barriers, one student (Harriet) had five barriers, three students (Andrew, Carlos, and Ian) had six barriers, and the remaining 5 students describe alternative conceptions explained by all seven of the barriers (see Table 4 for the distribution by conceptual barrier). Nearly half of students filling out the questionnaire (93 of 196) wrote at least one alternative conception that can be explained by the seven conceptual barriers (see Table 4 for the distribution by conceptual barrier). No obvious pattern was observed between the barriers students had with the introductory course in which they were enrolled or their achieving level in the introductory geology courses. The students also expressed many additional alternative conceptions and incorrect statements that were at a more “shallow” level, such as “granite is extrusive” and “basalt is shiny.” Many of these appear to be based on the students incorrectly remembering the features of a particular rock. Because the students filling out the questionnaires mostly did not go into depth in their answers, and because they were not probed for more information, the number of students answering the questionnaire holding alternative conceptions explained by the conceptual barriers is likely much higher. Many of the alternative conceptions explained by the conceptual barriers and the conceptual barriers themselves have been described by researchers examining students’ conceptions on geologic topics other than rocks and rock formation. For example, Dickerson and others (2005) described students’ difficulties with scale as an impediment for understanding groundwater. Many of the geoscience alternative conceptions listed by Kirkby (2008) can also be explained by the conceptual barriers described in this study. For example, the conceptual barrier of Deep Time explains the alternative conception, “Plate motion is rapid enough that continent collision can cause financial and political chaos, while rifting can divide families or separate a species from its food source.” Students do not realize that continents collide or divide over millions of years. Another example, “Rivers do not carve valleys, but only passively flow down them,” can be explained by the conceptual barrier of Changing Earth, since students view the valleys as always existing. Therefore, the conceptual barriers to rock formation as described in this study likely also apply to many other areas of geology. The conceptual barriers of geologic time (Deep Time as well as Changing Earth) and spatial literacy (Large Spatial Scale as well as Bedrock and Atomic Scale) identified in this study have been described by other researchers when discussing problems to learning geology in general. For example, Manduca and Mogk (2006) describe “three of the most fundamental characteristics of geoscience thinking [as] space, time, and complex 311 Journal of Geoscience Education, v. 57, n. 4, September, 2009, p. 300-315 systems” (page 51). Kastens and Ishikawa (2006) and Dodick and Orion (2006) discuss the spatial realm and geologic time, respectively, in detailed terms of how geoscientists think and learn about the Earth. Some of the barriers described in this study are unique to geology, while some are likely shared with other sciences. Alternative conceptions explained by the conceptual barriers of Atomic Scale and Pressure have been described in other sciences (e.g. Ben-Zvi et al., 1986; Henriques, 2000). However, because geology is a historical science that deals with immense time and distance scales, it has many unique aspects that make it different than other sciences. In particular, the barriers described in this study of Deep Time, Changing Earth, Large Spatial Scale, Bedrock, and Materials (in rocks) are all barriers that make geology uniquely difficult for students to understand. As a result of its uniqueness, geology needs to be taught differently than many other sciences. In particular, going out in the field is an integral aspect of learning geology and may help in reducing conceptual barriers (see below). Mental Models – Mental models, or cognitive models, are “an individual’s representation of a phenomenon, and are used to explain that phenomenon and predict outcomes” (Libarkin et al., 2003). For example, a student would create a mental model of how granite forms, and that student would use that mental model to answer questions and make predictions about granite. Since individual students have many of the conceptual barriers identified in this study, they cannot construct an appropriate mental model of rocks and how they form and change. In the example of granite, if a student does not have a correct conception of the conceptual barriers of Changing Earth, Large Spatial Scale, Bedrock, Materials, and/or Atomic Scale, they cannot form a scientifically- correct mental model of granite formation. Therefore, because the conceptual barriers exist in the students’ understanding, they cannot develop scientifically-correct mental models, so alternative conceptions result. A student’s prior conceptions of the Earth, such as the conceptual barriers identified in this study, dictate how new knowledge is perceived and organized within mental models. If a student does not realize that bedrock exists, they will not perceive rock formation as occurring in vast areas. If they do not consider that events can occur over millions of years, they will not understand the slow processes of metamorphism or uplift. Table 5 gives examples of typical statements an instructor (or geology textbook) may make and how it may be interpreted by students. The table was created by summarizing views expressed by students during the interviews. This potential interpretation by students is a result of them having scientifically incorrect mental models (resulting from the conceptual barriers) which cause them to integrate the instructor’s statement into non-scientific interpretations, creating alternative conceptions. Implications for Teaching – The results of this study have several implications for teaching geology. First, the instructor needs to be aware of the conceptual barriers. If the instructor does not know where students have difficulties in understanding rock formation, then they will not be able to effectively help students. Instructors may not initially find this necessary, since students may be answer exam questions relating to rock. However, Table 3 illustrates that reasonable statements made by students may actually be hiding incorrect mental models. Table 5 lists students’ possible interpretations to statements that the instructor may think are extremely clear and obvious. However, because of the underlying conceptual barriers carried by the students, these statements are often misinterpreted. If the instructor is not aware of this possibility, they will not be able to teach effectively. Second, it is important to make students aware of the barriers by directly talking about them. Learning should not be like a mystery novel, where students need to discover the barriers for themselves (because most will not!). Instead, present the students with some of the difficulties they may encounter when trying to learn geologic concepts. Third, even if students are aware of the conceptual barriers, it still may be very difficult for them to get past them. Not all the conceptual barriers are likely at the same difficulty level to learn, and some might be easier for students to get past. An example in geology where research has been performed is on the subject of deep time. Although research shows that it is extremely difficult for students to understand deep time, one way to help get the idea across is to use relative times (Trend, What the Instructor Says1 What Students May Interpret Granite is igneous. Granite is made up of sediments that are igneous. Pieces of granite come together in magma. Magma causes heat which fuses sediments to form granite. Metamorphic rocks form from heat and pressure. Heat is from the Earth’s core or volcanoes. Pressure is from heat or water. The heat melts the rock. Metamorphism can occur at the Earth’s surface, if the conditions are right. Sandstone forms in deserts. Desert sand can combine (often by drying) into rocks, at or right below the surface. Sandstone is found in the desert. It takes a long time for rocks to form. Rocks take 10 to 1000 years to form. Basalt erupts from a volcano. Solid basalt pieces come out of a volcano, sometimes in the lava. Sediments are often formed in mountains. Earthquakes and plate motion grinds rocks in mountains to form sediments. TABLE 5. STUDENT INTERPRETATIONS OF INSTRUCTION 1Among other explanations during lecture Research: Kortz and Murray - Barriers to Learning Rocks Education, v. 53, p. 394-401. Libarkin, J.C., Beilfuss, M., and Kurdziel, J.P., 2003, Research Methodologies in Science Education: Mental Models and Cognition in Education, Journal of Geoscience Education, v. 51, p. 121-126. 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You find out that a particular area was once an ancient mountain range that has since e r oded a w a y . What would you expect to see? A paleontologist determines that a group of dinosaurs once lived next to a shallow sea. How did the paleontolo- gist figure out that there was a shallow sea? A group of friends goes on a hike, and the oc- casionally pick up rocks along the way. All the rocks they pick up are gneiss and schist. What can they figure out about the area in which they hiked? A new planet is discovered, and there is limestone covering the sur- face. What can you figure out about this planet? You and a friend are examining a picture of a person holding a rock. You notice that the rock is ba- salt and the entire background in the picture is also ba- salt. What can you tell your friend about the area where the picture was taken? Tell me about the rock limestone. Tell me about the rock basalt. Tell me about the rocks schist or gneiss. 315 Journal of Geoscience Education, v. 57, n. 4, September, 2009, p. 300-315 granite APPENDIX B: INTERVIEW QUESTIONS The following questions were used as guides for the semi-structured interviews to learn about students’ con- ceptions of rocks. These questions were asked in no par- ticular order, and not all questions were asked during each interview. These questions were used to frame inter- views, but most questions asked were based on the re- spondents’ answers to previous questions. What is a rock? Tell me about this rock. [discussing a hand sample] How has the shape of this rock changed over time? What was this rock like before…? Where? When? What will this rock be like in the future? The past? If you wanted to go find rock like this, where could you find it? Where did this rock come from? How does this rock fit into what geologist call igneous, sedimentary, and metamorphic rocks? (note: Try not to use these words before the student does, but try to get at this idea. By the end of the interview, if it doesn’t come up, may ask a question such as: Some people say that this rock is an igneous rock…) Why do geologists study rocks? VERSIONS 1, 2, AND 3 Tell me about this rock: How do rocks change over extremely long periods of time? If possible, give examples. Why do you think you learn about rocks in this class? VERSIONS 4, 5, AND 6 Tell me about this rock: If you had to explain the rock cycle to a friend, what would you say? What can a rock tell you about its history?