New directions in Wilson Cycle concepts: Supercontinent and Tectonic Rock Cycles

Steven J. Whitmeyer* Lynn S. Fichter Eric J. Pyle Department of Geology and Environmental Science, James Madison University, Harrisonburg, Virginia 22807, USA

ABSTRACT environments by providing rapid interchange tem (lithosphere, atmosphere, hydrosphere, and between these two domains. Where factual biosphere) is dependent on interactions with the Modern earth science pedagogy is increas- information is of interest, e.g., when introduc- other components, through positive and nega- ingly based on an integrated systems frame- ing a topic or relaying important background tive feedback loops (Assaraf and Orion, 2005). work, where all of the major earth systems, information, the typical verbal primacy is In contrast, a review of pre-college and under- including lithospheric cycles, are interlinked observed. But in instances where spatial and graduate earth science curricula in the United and dependent on each other through feedback temporal relationships are of interest, such States suggests that earth science instruction is loops. Most secondary school and introductory as in the Rodinia and Pangaea superconti- still commonly organized into discrete bits of college-level geology courses present the con- nent cycles, and the “No Rock is Accidental” content. Generally speaking, learning objectives cepts of plate tectonics and rock classifi cations. tectonic rock cycle, the visualizations assume are arranged with elements such as landform However, many instructional approaches the primary role, with text-based annotations development, plate tectonics, and rock genesis fail to integrate these topics within an earth or verbal discussion as secondary. as separate, distinct topics, often with limited systems viewpoint, where supercontinent We conclude with discussions on the integrative connection (Hoffman and Barstow, cycles are viewed in both spatial and tempo- importance of inquiry-based educational 2007). The organization of these topics in a ral dimensions, and the classifi cation of rock approaches and effective ways of evaluating cause-effect fashion, or as a substantive part of types is intrinsically dependent on the tec- educational visualizations. We suggest that to an integrated system, is the exception, rather tonic, as well as the depositional environment best utilize the available media (digital and than the rule. in which they were formed. This contribution paper based), the level of cognitive engage- Not surprisingly, instructional materials refl ect presents new tectonic animations and images ment of the learning task should be closely tied this same descriptive and reductive organization. that allow students to investigate superconti- to a taxonomy of visualizations that encom- While many introductory college geology text- nent cycles (e.g., the assembly and breakup pass detailed, integrated representations and books present plate tectonic theory early in the of Rodinia, and the Paleozoic interactions animations. Inquiry-based interfaces, such as text as an organizing and potentially unifying of Laurentia, Gondwana, and Baltica) and we present in this paper, promote more mind- theme, most pre-college earth science texts pro- integrated Wilson Cycle and Tectonic Rock ful articulations of the desired learning tasks vide information on plate tectonics in a manner Cycles that equate rock genesis with tectonic and an increased retention of the subject that precludes connections with rock generation and environmental settings. Central to these material outside the bounds of the classroom. or landform development (Chambliss and Cal- visualizations is the concept that processes of Teaching a systems-based understanding of fee, 1989). As a result, the generation of rocks rock genesis have evolved, and will continue the Earth and the concepts of evolving tec- and landforms are disconnected from the tec- to evolve, through geologic time. We discuss tonic and rock cycles provides students with tonic and environmental processes that generate the conceptual and historical background for holistic foundations from which they can bet- them. Discussions of plate tectonics are limited each of these visualizations, and follow this ter evaluate, and make decisions about, their to paleontological and geophysical evidence for with detailed descriptions of, and educational living environment. the theory, such as Glossoptera fossils, volcano uses for, the images and animations. and earthquake occurrences, and paleomagnetic To be of optimal instructional utility, the Keywords: plate tectonics, Rodinia, Laurentia, data. More importantly, students are commonly animations and images consider the visual Wilson Cycle, rock cycle presented with a truncated depiction of global domain as a primary, rather than secondary tectonic history that only encompasses the instructional tool. As such, they are designed INTRODUCTION breakup of Pangaea (ca. 200 Ma) to the present, to function optimally in an inquiry-driven with prior supercontinent cycles represented, educational setting. They take into account Modern approaches to earth science educa- if at all, only in a discussion of geologic time the complex cognitive interactions between tion are increasingly focused on “systems think- (e.g., Tarbuck and Lutgens, 2005). The breakup visual and verbal representations in learning ing,” wherein each component of the earth sys- of Pangaea is presented as an isolated system,

*[email protected]

Geosphere; December 2007; v. 3; no. 6; p. 511–526; doi: 10.1130/GES00091.1; 8 fi gures; 3 animations.

For permission to copy, contact [email protected] 511 © 2007 Geological Society of America

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and the dynamic nature of the Earth’s evolution- variables operating. “Prediction” in this sense introduced into the introductory classroom. In ary history is merely implied. In rock genesis, is not the same in the earth sciences as it is addition, as scientifi c ideas evolve, they tend where the three rock “types” (igneous, sedimen- in classical science. In complex systems like to become more complicated, and more diffi - tary, and metamorphic) are unifi ed through the the Earth, theories are less likely to predict a cult to teach. However, ideas and theories do ubiquitous “rock cycle” diagram, relationships specifi c outcome but rather an explanation progress in accuracy and complexity, and at are presented as a closed loop, with little regard of the underlying mechanisms at work; e.g., some point teaching what is simple and famil- for how the types and volumes of rocks on Earth under a particular set of conditions, a certain iar does both the discipline and the student a have evolved through billions of years of the set of structures and rocks will form. Time is disservice. Decision making in these cases is Earth’s tectonic history. an essential component, because the slow rates not clean and simple; academia benefi ts from Part of the handicap with presenting topics of tectonic and evolutionary processes require the dynamic tension between conservative like the Earth’s dynamic history and rock genesis millions or billions of years to accomplish the foundations and new directions precipitated as integrated systems is that textbooks and even signifi cant changes apparent in the rock record. by modern research. In the following sections PowerPoint illustrations are primarily descrip- This viewpoint is fundamental in the earth sci- of this paper, we argue that theories about the tive rather than generative, wherein complex ences, where time is used in a forward and Earth’s tectonic processes have evolved to the dynamic processes are reduced to static images. backward manner—predictions as well as “ret- point where we need to reevaluate what we Comprehension is also made diffi cult by the rodictions” (Frodeman, 1995). teach and how we teach it. We begin with a range of scales of observation at which Earth Earth scientists are still a long way from fully brief summary of how rapidly changing scien- processes function—from the microscopic to explaining or integrating how the complex world tifi c ideas have infl uenced the teaching of earth the global and from microseconds to hundreds works, i.e., how all the Earth’s systems interact tectonics over the past half century and then of millions of years. Integration of these pro- to produce the outcomes we observe. However, discuss why existing depictions of tectonic cesses into an effective instructional approach we now appreciate the necessity of viewing the cycles and rock cycles in educational materi- is an ongoing challenge, and it is within this Earth and teaching Earth’s history in the context als need further refi nement within a broader time-dependent, process-oriented framework of interconnected and interdependent complex earth systems context. that modern computer-aided visualizations can systems. This contribution presents spatial and be effectively utilized. temporal animations of plate tectonic processes Geosynclinal Theory to Modern Tectonic The educational potential for visualizations and sequential diagrams of modern Wilson Models has been recognized by the American Associa- Cycles and Tectonic Rock Cycles that integrate tion for the Advancement of Science (AAAS), tectonic processes and rock genesis in an evolu- Before the majority of American geosci- through the textbook analysis framework devel- tionary framework. We expect that these anima- entists accepted that continents moved, the oped by Project 2061 (Kesidou and Roseman, tions and models will help secondary through governing tectonic theory from the last half 2002). Their framework includes, as a criterion, undergraduate educators teach rock cycle and of the nineteenth century into the late 1960s “relevant phenomena”—that is, real-world tectonic concepts as an integrated, time- and was geosynclinal theory. Emanating from the examples or illustrations of scientifi c concepts space-dependent, evolutionary system. By ani- Appalachians-focused work of James Hall requiring, in part, a vicarious sense of observa- mating complex continental movements over (1811–1898) and James Dana (who coined tion of phenomena. Project 2061 showed that nearly a billion years of history, but in tempo- the term geosyncline in 1873), geosynclinal while scientifi c visualizations are common in ral and spatial frameworks humans can grasp, theory tried to explain mountain building in most science textbooks, their connections to students can begin to appreciate not only the the context of a cooling and shrinking Earth the text materials and the overall concepts do complexity of tectonic movements but also the from an originally molten state. Marshall Kay not provide the direct support for student learn- continuity of a set of recurring processes, such (1952) published the culminating synthesis ing that teachers, parents, and adoption com- as continental collisions and supercontinent of geosynclinal theory, and since Kay and mittees envisioned, relative to the curricula for assembly and breakup. From this appreciation, most other American geologists at the time which the textbooks were intended. In the non- we hope to demonstrate predictability—not were working from a “fi xidist” assumption earth sciences, such visualizations are possible specifi c predictability, such as 500 million years (continents do not move), mountains were as demonstrations or laboratory experiments; from now two continents will collide in a cer- depicted as forming in place without laterally we can observe in real time animal behavior, tain way—but, rather, predictions such as when directed outside infl uence. This interpretation or a swinging pendulum, or the results of a two tectonic blocks interact in a particular way, is apparent in a series of block diagrams from chemical reaction. The same is not true for the the same kinds of rocks and structures will be Brice (1962; Fig. 1) that provides a pre–plate generation of a granite body, the growth of a generated by the same kinds of processes. With tectonic interpretation of mountain building. mountain, or the movement of continents, all each continental collision, uniquely differ- However, it is important to recognize that, in of which occur within timeframes much longer ent mountains are formed, but they are similar general, European geoscientists were quicker than human observation. enough that we can deduce and predict common to accept continental drift and early plate tec- The earth sciences are distinct from the processes. tonic theory than their American counterparts classical sciences in other fundamental ways. (Oreskes, 1999). Arthur Holmes presented a Although earth scientists often conduct labora- CONCEPTUAL BACKGROUND remarkably accurate depiction of continental tory experiments in the classical framework of drift and mantle convection in his 1944 intro- a single dependent variable, fi eld examination It is not wise for teachers and textbook ductory geology text (Holmes, 1944), and by of a rock outcrop yields data that incorporates authors to chase after every new idea that the mid-1950s, paleomagnetic data was caus- the sum total of all generative processes that comes along, because ideas and theories need ing European fi xidist stalwarts, such as Keith occurred at many scales of action, over many to mature (i.e., be validated and accepted by Runcorn, to embrace drift theory (Runcorn, scales of time. Inevitably there are unknown the scientifi c community) before they are 1955, 1956).

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Geosynclinal concepts such as those in Fig- ure 1 strongly infl uenced the generation of American geologists who contributed to the early development of plate tectonic theory in the 1960s and 1970s (Oreskes, 2001). During these formative years, many plate tectonic aspects of mountain building were explicitly described using geosynclinal terminology (e.g., Atwater, 1970; Bird and Dewey, 1970; Dewey and Bird, 1970; Dickinson, 1971; Gilluly, 1971), since that was the accepted language that addressed mountain divisions, structure, and formation. As plate tectonic theory came of age during the late 1970s and early 1980s, a whole new set of terminology developed, consistent with newly recognized divisions and mechanisms. In the interim, however, two sets of terminology were present in both the scientifi c literature and in textbooks (e.g., Verhoogen et al., 1970; Press and Siever, 1974). An example of this transition period is seen in the cross sections of Dietz (1972; Fig. 2), where early plate tectonic and vestigial geosynclinal concepts are both in evidence: “The concept that the geosynclinal cycle is controlled by plate tec- tonics provides some new answers to old ques- tions about geosynclines” (Dietz, 1972, p. 108). Dietz made extensive use of the terms miogeo- cline and eugeocline (taking the “syn” out since they are no longer synformal in his reconstruc- tions), but placed them in a plate tectonic con- text. In addition, the Dietz model makes explicit the opening and closing of ocean basins, which is implicit in the geosynclinal diagrams of Brice (Fig. 1). Building on the paleogeographic maps of Dietz and Holden (1970), Dietz (1972) not only opens and closes the Paleozoic ocean basin, he extends it to include developing models of Pangaea. This model was important not just to the geoscience research community, but also because it proliferated in introductory geology textbooks (e.g., Press and Siever, 1978), incul- cating a new generation of geoscientists and lay Figure 1. Block diagrams showing six stages in the development of geosynclinal moun- people alike in how plate tectonics infl uenced tain building; after Brice (1962). (A) Pre-orogenic miogeosyncline characterized by shal- Atlantic geologic history. low-water carbonates, quartz-rich sandstones, no volcanics, and relative tectonic stability. A major problem with these early tectonic Observe that on the eastern (right) side, the geosyncline seems to transition vaguely into models (Dietz, 1972; Bird and Dewey, 1970) something, but it is unspecifi ed. (B) A volcanic arc rises up on the outside fl ank (ocean side, is that they depict Appalachian mountain belts away from the craton) of the miogeosyncline, converting it into a deepwater eugeosyncline, as generated by west-dipping subduction of an while the miogeosyncline subsides into an exogeosyncline. The exogeosyncline fi lls with oceanic plate. This assumption was implicit in immature deepwater sediment (“graywacke,” a.k.a. fl ysch) eroded from the volcanic arc/ geosynclinal theory where volcanic arcs were eugeosyncline lying beside it, interbedded with underwater lava fl ows. No magma source for located in the eugeosyncline (Kay, 1952), and the volcanic arc is indicated in the cross section, but since we fi nd the remnants of the arcs this geometry was adapted to early plate tec- in the Piedmont today, it is presumed they formed in place at those locations in the past. (C) tonic models to generate Appalachian volcanic Granites intrude the eugeosyncline, leading to widespread metamorphism, accompanied arcs with west-dipping subduction zones. The by compression leading to folding, faulting, and mountain uplift. Subgraywacke sediments assumption that volcanic arcs always formed (a.k.a. molasse) are deposited across the “delta coastal plain,” mostly in rivers and shallow in situ was challenged originally in studies of marine environments. (D) and (E) Mountain building has ended, and all that remains is for the Cordilleran region, where evidence pointed the mountains to be eroded down. (F) Graben formation, corresponding with the Triassic to the existence of suspect terranes (Hamilton, basins of the Atlantic coastal plain and Piedmont. 1969; Irwin, 1972; Ernst, 1975). However, as

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Figure 2. An early set of cross sections showing the Wilson Cycle. This model is a synthesis of geosynclinal concepts and plate tectonic con- cepts based on interpretations of Appalachian and European geology; after Dietz (1972).

the full consequences of the suspect terrane idea (Hatcher, 1989, among others). Instead of sub- 1983; Nance et al., 1991; Dennis and Wright, became appreciated in the Appalachian context, duction zones that dipped westward under North 1997). Today, the majority of Appalachian sus- it led to a complete reversal of thinking about America, newer models showed them generally pect terranes are no longer considered “sus- the closure of the Iapetus (proto-Atlantic) ocean dipping eastward (Hatcher, 1972; Secor et al., pect”; geologic, paleontologic, and geophysical

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studies confi rm their exotic origins (Hatcher et how they relate to one another and to the and Karlstrom, 2007). (3) Within the past bil- al., 1989; Williams, 1995; Hatcher et al., 2004). whole.” lion years, at least two major supercontinents, For our purposes, the main point is that the mod- In addition to higher order thinking skills, Rodinia and Pangaea, assembled and dispersed els of Dietz (1972) and Bird and Dewey (1970), systems thinking encourages the ability to ana- (McKerrow and Scotese, 1990; Moores, 1991; because they quickly infi ltrated the teaching lit- lyze different parts of a system simultaneously, Li et al., 2007), and the associated history of erature and the classroom, strongly infl uenced at scales ranging from the microscopic to the continental movements is neither simple nor the thinking of many geologists. They were macroscopic (Hmelo et al., 2000; Kali et al., straightforward. simple, slick, neat models; they were relatively 2003), and “the ability to identify relationships The implications of these ideas infl uence easy to teach; but they don’t represent our cur- among the system’s components and organize existing models that are, or have been, deeply rent understanding of earth processes, and we the system’s components and processes within imbedded in geoscience teaching, and that need no longer teach them. a framework of relationships” (Assaraf and rethinking. The problem is that many previous Orion, 2005, p. 523). Kali et al. (2003) focused and existing models have been useful educa- Geologic Systems Thinking on students’ understanding of a traditional rock tional tools; however, they no longer represent cycle. Their goal was an explanation that went modern understanding of the Earth. An example Terms like system, complex system, complex beyond a static view of the system and con- of this is the tectonic model of Wilson (1966), systems theory (a.k.a. chaos theory), earth sys- tained “highly developed dynamic thinking of which is often termed the “Wilson Cycle.” In tem, and earth system science are used ever more material transformation within the rock cycle, the early days of plate tectonic theory, Wilson’s frequently in the modern earth science lexicon. and a rich understanding of the interconnected- (1966) original map-view model of the Atlantic Part of our goal in this contribution is to develop ness between parts of the system” (p. 558). They closing and then reopening (see Animation 11) visualizations that help students develop high- concluded that students possessed “chunks” of and Dietz’s (1972) cross sections (Fig. 2) that order systems thinking skills about the Earth. process knowledge, e.g., material transforma- epitomize the Wilson Cycle concept were com- We frequently use the term “system,” but unfor- tion in the rock cycle, that are initially specifi c mon in text books (Press and Siever, 1978) and tunately, system concepts are used differently and disconnected from each other (low-level classrooms. Today, however, we recognize that in different disciplines and are evolving rapidly systems thinking). Specifi cally, students exhib- these early depictions of orthogonal collisions (Shufeldt, 2007). A common characteristic of ited problems with making full, dynamic con- and symmetrical extensional collapse of North systems across disciplines is that systems exist nections between different parts of the rock America with Africa and Europe are far too and function as a whole, while depending on the cycle. To move beyond such limitations, a simplistic. Modern reconstructions depict the interactions of their parts through positive and dynamic, systems thinking approach to instruc- negative feedback loops (Assaraf and Orion, tion is required to associate initial “chunks” to 2005). Each component has a specifi c purpose, broader ideas (high-order systems thinking). and therefore each component must be func- The visualizations presented in this paper tioning for the whole system to perform ideally. are driven by systems-oriented ideas, even if A full exploration of systems theory is beyond not explicitly stated. However, teaching from a the scope of this paper, but we need to briefl y systems perspective should not be approached address two systems-oriented concepts that are lightly. Systems thinking about the Earth as a relevant to the visualizations and educational whole requires high-order and critical thinking approaches we propose: skills that many students are not accustomed to, (1) Students need to think about the Earth, not and many faculty are not used to teaching (at least as isolated parts, but as a system wherein at the pre-college and undergraduate levels). It is all components are interconnected through our intention that the accompanying visualiza- positive and negative feedback mecha- tions will help to make this complex teaching task nisms. When talking about “earth sys- more comprehensive and intuitive. tems science,” this usually encompasses the relative infl uences of the lithosphere, Implications for Earth Science Teaching Animation 1. QuickTime movie of Wil- atmosphere, hydrosphere, and biosphere son’s (1966) original Atlantic closing and on each other. In this paper, we focus on New models of the Earth’s evolution that then reopening “cycle.” Note the basically lithosphere processes, but with the same incorporate integrated systems theory have orthogonal collision of Europe (orange) and goal of inculcating thinking about how radically changed our depiction of historical Africa (orange) with North America (blue), rock genesis and tectonics are inextricably and present-day tectonics, but these concepts with no depiction of rotational or latitudi- intertwined. and their larger implications have not yet been nal complications of 3D geometry. Breakup (2) Student use of systems thinking about the adequately incorporated into classrooms and is along similar orthogonal lines, although Earth will aid in the development of higher textbooks. These concepts include: (1) Earth some consideration of rotational motion order thinking skills (Kali et al., 2003; originated with no, or at best, only small con- of North America and Europe relative to Assaraf and Orion, 2005). As phrased in tinental blocks, and the continents have grown Africa is inferred. a report by the American Association for with time (Windley, 1995; Condie, 1997; Whit- the Advancement of Science (1993, p. meyer and Karlstrom, 2007). (2) Today’s con- 1If you are viewing the PDF of this paper or read- 262): “One of the essential components tinents are composed of many smaller crustal ing it offl ine, please visit http://dx.doi.org/10.1130/ GES00091.S1, http://dx.doi.org/10.1130/GES00091. of higher-order thinking is the ability to components and did not reach their present con- S2, and http://dx.doi.org/10.1130/GES00091.S3 or think about a whole in terms of its parts fi guration until recently in Earth’s history (Hoff- the full-text article on www.gsajournals.org to view and, alternatively, about parts in terms of man, 1988; Karlstrom et al., 1999; Whitmeyer the animations.

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Neoproterozoic-Early Cambrian opening of on a three-dimensional globe. However, these result of transferring heat between two sources the Iapetus ocean with ancestral South Amer- fundamental concepts are intricate and often at different temperatures without any contact ica (the Rio de La Plata and Amazon cratons) diffi cult to teach effectively without the use of between those sources. The circular rock rifting away from Laurentia (ancestral North modern computer-aided animations. cycle transforms one rock into another with- America; Fig. 3), while the Late Paleozoic A more serious implication of new tectonic out acknowledging that these transformations closing of the Rheic ocean culminates with the theories is that the traditional, circular rock cycle take place in specifi c tectonic regimes, on a collision of Laurentia and the African part of universally presented in textbooks and taught planet that has evolved substantially since its Gondwana (Fig. 4). These modern plate recon- in classrooms—and the Huttonian/Lyellian origin, and where the diversity and abundance structions reveal important complexities, such uniformitarian philosophical principle behind of rocks has changed through time. Modern as the rotational movement of plates (McKen- it—is no longer valid. A circular rock cycle theories of the Earth and its processes suggest zie and Parker, 1967; Morgan, 1968) and trans- is analogous to Carnot’s (1824) model of an that we need integrated models that illustrate form boundaries (Wilson, 1965), as required ideal heat engine, which has the rather tricky how rock genesis, rock transformations (e.g.,

Figure 3. The Rio de La Plata and Amazon cratons rifting away from Laurentia (ancestral North America).

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rock type associations. Our experience suggests that the benefi t of increased comprehension from students outweighs the geometric approximations in these visualizations.

Supercontinent Cycles

One of the principal shortcomings of repre- sentations of plate tectonic cycles in many intro- ductory geology texts is the restriction of histori- cal plate movements to the period from the full assembly of Pangaea (ca. 250–200 Ma) to the present day (e.g., Holt, Rinehart, and Winston’s Modern Earth Science, 2002). This is largely the result of historical precedent; the early Con- tinental Drift concepts of Wegener (1912) began with a supercontinent that he called Gondwana (now termed Pangaea) and followed the move- ment (drift) of the continents to their present-day positions. Wilson (1966) recognized that this “breakup” of Pangaea was only part of the story: Pangaea must have assembled from existing con- tinental fragments before it could later break apart (e.g., Animation 1). In some textbooks, the forma- tion of ancient mountain ranges is depicted, but usually as an illustration of convergent margins Figure 4. The closing of the Iapetus ocean culminates with the collision of Lau- (e.g., McGraw-Hill’s Earth Science, 2002). The rentia and the African part of Gondwana. origin of the preexisting fragments is left some- what open. Past plate positions are often depicted, but usually in the context of geologic time periods rock cycles), climate, and tectonic models we focus on: (1) computer animations that depict and not as a function of rock formation. A com- work together (Dickinson and Sucek, 1979; modern concepts of “supercontinent cycles” as prehensive model of supercontinent cycles is at Earth System Science Committee, 1986; Stef- spatially correct depictions of the assembly and best only implied. fen et al., 2004). More importantly, these must breakup of supercontinents within the past 1.1 bil- In the 40 years since Wilson’s seminal paper be in a form that can be incorporated into col- lion years of Earth’s history; (2) a heuristic Wilson (1966), we have recognized that Paleozoic plate lege introductory geology classrooms and Cycle developed as a series of cross sections that movements and continental interactions are simplifi ed for secondary school classrooms. elucidate the plate tectonic conditions under which far more complicated than Wilson originally With this in mind, the text that follows pres- specifi c rock types and structures form; and (3) a described, although we suspect that Wilson ents visualizations and animations of super- Tectonic Rock Cycle that combines traditional had a good appreciation for these complexi- continent cycles, Wilson Cycles, and rock circular rock cycle concepts with specifi c plate ties back in the 1960s. The Neoproterozoic cycles based on our current understanding of tectonic processes. The visualizations we present breakup of Rodinia quickly produced another the integrated earth system. These have been in this paper are not devoid of simplifi cations and smaller supercontinent, Gondwana, composed designed as teaching tools to be used in interac- distortions, however. The map-view animations of the present-day continents of Africa, South tive classroom environments, but we recognize are 2D representations of continental movements America, Antarctica, and Australia, as well as that these tools are just a subset of the materi- around a 3D globe. In an effort to minimize stu- continental fragments, such as India, Florida, als necessary to effectively educate students in dents’ comprehensive diffi culties with distorted and Avalonia (Hoffman, 1991; Dalziel, 1991, the amazingly complex earth system. We fol- landmasses, we have treated the globe as if it were 1995). Other isolated Paleozoic continents low discussions of the individual visualization a fl at surface and removed projection-derived dis- included Baltica (present-day Scandinavia and products with a section on the educational and tortions of the continent’s shapes. Each animation northern Europe) and Laurentia (most of pres- cognitive implications for this relatively new has a distinct focal point: the Rodinia animation ent-day North America). Gondwana spent much systems-based approach to teaching integrated (#3) shows the continents relative to Laurentia, of the Paleozoic rotating around the South Pole; earth processes. and the Laurentia-Gondwana animation (#2) indeed Wegener (1912) used evidence of early shows Paleozoic movements relative to the South Paleozoic glaciations to connect many of the MODERN DEPICTIONS OF EARTH Pole. These focal points magnify distortions at continental components of Gondwana. Dur- SYSTEM CYCLES the boundaries of the images, but our goal was to ing this period of time, Laurentia and Baltica maximize student comprehension of plate tectonic rotated around Gondwana in a predominantly One of the main purposes of this contribution is relationships during the highlighted time periods. clockwise motion (Dalziel, 1995, 1997; Roberts, to advocate the use of more advanced (and more Similarly, the Wilson Cycle cross sections are 2003) before colliding with Gondwana at the end accurate) earth system “cycles” as modern, up-to- somewhat cartoon-like, with some vertical exag- of the Paleozoic to form Pangaea (Dietz and date teaching devices. In the following sections, geration and enlargement of critical tectonic and Holden, 1970; McKerrow and Scotese, 1990;

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Lawver et al., 1998). The interactions between A recent multinational effort (the Interna- Laurentia and Gondwana during this period tional Geoscience Programme [IGCP] 440 are highlighted by the transfer of two micro- project) has produced the most detailed Rodinia continental terranes—the Laurentia-derived reconstruction to date (Li et al., 2007) and, in Precordillera and the Gondwana-derived Avalo- the process, highlighted a critically underap- nia. Thomas and Astini (1996) determined that preciated concept. Simply stated, the various the Precordillera terrane rifted from the Texas continental components of supercontinents do embayment region of southeastern Laurentia in not all assemble at the same time: superconti- the early Cambrian, migrated across the Iapetus nent assembly is diachronous. Several conti- ocean, and collided with the western margin of nental blocks, such as South China and Siberia, Gondwana (present-day western Argentina) in were already accreted to northwestern Laurentia the late Ordovician to early Devonian. In con- by 1100 Ma, followed by eastern components trast, the microcontinent of Avalonia traveled (Baltica, Amazon, and the African blocks) at from northern Gondwana to eastern Laurentia, ca. 1000 Ma. Full assembly of Rodinia culmi- the opposite direction across the Iapetus, in the nated with the accretion of Australia and Ant- late Ordovician-Silurian (Murphy et al., 2002; arctica (with India) to southwestern Laurentia Keppie et al., 2003; among others). Baltica Animation 2. QuickTime movie of the rela- at ca. 900 Ma (Karlstrom et al. 1999; Li et al., moved independently for most of the period, tive positions of Laurentia (pink), Gondwana 2007). Thus, the assembly of the Rodinia super- prior to joining the northern extent of Avalonia (gray), and Baltica (green) from the Neopro- continent consisted of a protracted sequence of just before their Silurian-Devonian collision terozoic to the Late Paleozoic, leading up to continental terranes that accreted to the Lau- with eastern Laurentia during the Acadian orog- the assembly of Pangaea. Included are sig- rentian core over more than 200 million years. eny (Roberts, 2003; among others). nifi cant microcontinental movements—the Animation 3 (see footnote 1) is a QuickTime The simple diagrams of Wilson (1966) and Laurentia to Gondwana transfer of the movie that illustrates this diachronous assembly Dietz (1972) barely hint at the Paleozoic tectonic Precordillera terrane and the Gondwana to of Rodinia, and also demonstrates that, while complexities described above. However, simple Laurentia transfer of Avalonia. Movements Laurentia is close to the dimensions of pres- tectonic illustrations that vary little from these 40- are shown relative to the South Pole (SP). ent-day North America by 1.0 Ga, one is hard yr-old models persist in many modern textbooks, Laurentia and Gondwana movements are pressed to discern the shapes of present-day and thus do a poor job of illustrating plate tectonic largely based on Dalziel’s (1991, 1995, 1997) history as we now understand it. This is likely depictions of the “end run” clockwise move- because it is diffi cult, if not impossible, to fully ment of Laurentia around Gondwana dur- comprehend the Paleozoic tectonic movements of ing the Paleozoic. Locations of Baltica are the major continents and microcontinental frag- largely based on Roberts (2003). Transfer ments with verbal descriptions (demonstrated by of the Precordillera microcontinent (pink) the diffi culty of keeping track of and visualizing from the Ouachita embayment region of continental movements solely from the descrip- southeast Laurentia to the western South tions in the last paragraph), or traditional, static America region of Gondwana is based on map-view or cross-sectional images. However, Thomas and Astini (1996). Transfer of Ava- interactive computer animations are an ideal lonia (gray) from the north African margin medium to allow students to explore our modern of Gondwana to eastern Laurentia based on understanding of Paleozoic plate interactions that Roberts (2003) and Keppie et al. (2003). led to the assembly of Pangaea. Animation 2 (see footnote 1) shows the movements of Laurentia, Gondwana, Baltica, and the Precordillera and Ava- step and ask whether supercontinents, in addition Animation 3. QuickTime movie of the dia- lonia microcontinents from the Neoproterozoic to Gondwana, existed prior to Pangaea. Indeed chronous assembly and breakup of Rodinia breakup of eastern Rodinia (ca. 600 Ma) to the we now recognize the possible existence of sev- from 1100 Ma to 530 Ma. Positions of con- assembly of Pangaea (ca. 250 Ma). The Quick- eral early supercontinents, such as “United Plates tinental fragments (white) relative to Lau- Time interface allows the user to view the images of America” (Hoffman, 1988), “Nuna” (Hoffman, rentia (multi-colored) at key time slices as a continuous movie, or to advance through the 1997), and “Columbia” (Rogers and Santosh, (e.g., 1100 Ma, 1000 Ma, 900 Ma, 700 Ma, sequence step by step, either forward or backward. 2002), among others. The most robust reconstruc- 550 Ma) based on the IGCP 440 reconstruc- This puts students in control of an inquiry-based tions of a pre-Pangaea supercontinent depict an tion of the Rodinia supercontinent, as sum- learning process, and teachers can propose “What assembly of most existing continental fragments marized in Li et al. (2007 and references if” questions to enhance the students’ understand- at ca. 1.1–0.9 Ga as the supercontinent Rodinia. therein). Development of Laurentia during ing of the complex tectonic scenarios. Early proposals for a ca. 1.0-Ga supercontinent this time period based on Whitmeyer and (Moores, 1991; Dalziel, 1991) showed part of the Karlstrom (2007). Early Cambrian rifting The Diachronous Assembly and Breakup of story with Australia and Antarctica attached to of the Precordillera micro-continent from Supercontinents western North America (Laurentia). Subsequent Laurentia based on Thomas and Astini reconstructions (Karlstrom et al., 1999; Sears and (1996). Neoproterozoic-Cambrian assembly After investigating Paleozoic tectonics leading Price, 2000; Meert and Torsvik, 2003; among of Gondwana following breakup of Rodinia up to the formation of the Pangaea superconti- others) have modifi ed these early depictions and largely based on Powell et al. (1993) and nent, students often recognize the next logical added more pieces to the puzzle. Dalziel (1997).

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South America and Africa from the Proterozoic but many of the intrinsic ideas are still relevant The multistage Wilson Cycle equates time- continental blocks of Rio de La Plata, Ama- and can be effectively applied within a modern dependent tectonic processes with characteristic zon, Kalahari, Congo, San Francisco, and West Earth systems context. We have modifi ed and rock-forming environments, and thus facilitates Africa. This evolutionary growth and assembly expanded on these original Wilson Cycle con- the integration of mineralogy, petrology, passive of smaller continental fragments into present- cepts to produce a generalized Wilson Cycle margin stratigraphy and deformation with tec- day continents is a critical earth systems concept (Fig. 5) that can serve as a globally applicable tonics in a full earth system. Through the use and will be further addressed in the “heuristic heuristic model. Such a model should equate a of these cross sections in an inquiry-based edu- Wilson Cycle” section below. recognizable sequence of major tectonic events cation setting, students should readily grasp the The breakup of supercontinents is also a dia- that occur throughout the lifespan of an ocean interconnectedness of tectonic environment with chronous process. Breakup of Rodinia began basin to typical conditions under which igneous, rock type. From this point, it is only a small step along the west coast of Laurentia (ca. 780– sedimentary, and metamorphic rocks occur. For to the realization that if tectonic environments 685 Ma), 200–150 million years prior to suc- example, a heuristic Wilson Cycle should explain and continents evolve with (geologic) time, cessful breakup of Rodinia along the east the variety of pressure/temperature (P/T) condi- then rocks and rock types must also evolve. At coast of Laurentia (ca. 600–535 Ma; Hatcher, tions under which metamorphic rocks form: low this point, it becomes clear that the traditional, 1989; Powell et al., 1993; Hatcher et al., 2004; P/T, HP/LT, high P/T, etc., as well as the range of closed-loop rock cycle diagram is conceptually Thomas, 2006), as shown in the closing frames depositional environments for sedimentary rocks, fl awed—even for the beginning earth science of Animation 3. The same is true for the breakup and the sources for compositional differences of student. of Pangaea: the rifting of North America and igneous rocks. An important corollary of this is Africa/Eurasia opened the northern Atlantic that ambient P/T conditions recorded in meta- Tectonic Rock Cycle Ocean ~60 million years before the rifting of morphic rocks are only preserved by rapid exhu- South America and Africa opened the southern mation from tectonic and/or climatic processes. The simplest model we have of earth pro- Atlantic (Dietz and Holden, 1970; Scotese and The detailed, nine-stage Wilson Cycle cesses is the circular rock cycle (Fig. 6). It sum- Sager, 1988). These “details” of global tecton- depicted in Figure 5 (Fichter, 1999a; Fichter and marizes a core concept of geology: all rocks are ics are more than just complications of existing Pyle, 2007) incorporates major tectonic events related to each other and can be transformed simple models. The use of interactive anima- in the context of the lifespan of an ocean basin from one to the other. The cycle is the most the- tions allows students to appreciate the subtleties (full Wilson Cycle). It begins with one hypothet- oretically abstract description of these rock rela- of global tectonic movements and fi nish with a ical supercontinent and ends with another and tionships: it incorporates or is expandable to all better understanding of subcrustal convection illustrates rifting processes, ophiolite formation, rock processes, but does not necessarily specify and plate movement on the Earth’s three-dimen- island arc orogenesis, arc-continent collisions, or justify them. It also suggests the pathways sional surface. In addition, the evolving and cordilleran-type orogenies, and continent-conti- by which one rock can transform into another, cycling supercontinent system helps reinforce nent collisions. Climate-driven erosion of sedi- but does not explicate the necessary conditions the concept of the gradual evolution of earth ments, followed by deposition in grabens and under which these transformations take place. systems at geologic (i.e., slow!) rates through- passive margin environments and lithifi cation The simplicity of the circular rock cycle pro- out 4.5 billion years. as sedimentary rocks, is illustrated in the exten- vides a framework for rock genesis that can sional stages (Figs. 5B–5D). Metamorphism of be easily understood by most students. How- Modern Heuristic Wilson Cycle existing rocks is apparent in the collisional envi- ever, the traditional circular rock cycle fails to ronments of Figures 5E–5G. The formation of incorporate fundamental feedback relationships When Wilson (1966) asked “Did the Atlantic igneous rocks is apparent in many of the stages between tectonics, climate, and rock genesis. Close and then Re-Open” he provoked the idea as decompression melting (Figs. 5B–5D) and as The circular rock cycle also implies that that ocean basins have a life history—a recog- melting induced by dewatering of subducting rocks cycle endlessly from one to the other, nizable beginning, ending, and rebirth. Initially, slabs (Figs. 5E–5G). with no evolutionary change through time. Wilson was mainly concerned with Appalachian The heuristic Wilson Cycle also contains fun- Thus, it refl ects the nineteenth century unifor- mountain building (closing of the Iapetus ocean) damental evolutionary components: continents mitarian school of thinking, captured best by followed by subsequent rifting (opening of the enlarge and new juvenile crust (i.e., igneous James Hutton (1788), when he said the Earth Atlantic Ocean; see Animation 1). This origi- rocks) is generated through accretionary events has “no vestige of a beginning, and no pros- nal presentation of the “Wilson Cycle” concept (Windley, 1995; Whitmeyer and Karlstrom, pect of an end.” Contrast that with the heu- was out of phase with subsequent depictions of 2007). For example, as compared with the stage ristic Wilson Cycle described above, wherein “Wilson Cycles” that began with the opening of A continent (Fig. 5A), the stage I continent continents grow with time, largely through the an ocean basin. For example, Dietz (1972) illus- (Fig. 5I) is signifi cantly larger and contains generation of intermediate and felsic igneous trated one and one-half Wilson Cycles (opening more intermediate to felsic igneous rock. This rocks. N.L. Bowen (1912) determined the frac- and closing of the Iapetus, followed by opening results from the formation of a volcanic arc that tionation process by which felsic igneous rocks of the Atlantic). These early models were revo- accretes to the Westcontinent during the fi rst were generated from a more mafi c parent, and lutionary in their introduction of tectonic cycles closing phase (Figs. 5E–5F), and Cordilleran extrapolation of that process suggests that the and ultimately led to more recent models for the plutonism and metamorphism that takes place on composition of igneous rock suites must have assembly and breakup of supercontinents like the margin of the Eastcontinent during the sec- evolved through geologic time. Igneous rock Pangaea (Scotese and Sager, 1988) and Rodinia ond closing phase of the model (Figs. 5G–5H). evolution is supported by less evolved igneous (Li et al., 2007). This sequence refl ects our current understand- rock suites, such as Archean greenstone belts The models of Wilson (1966) and Dietz ing that new intermediate and felsic continental and TTG (tonolite, trondhjemite, and grano- (1972) are location specifi c (eastern Laurentia/ igneous rock is generated with each subduction diorite) suites and Proterozoic AMCG (anor- North America) and, in part, historically dated, zone, and continents thus grow with time. thosite, mangerite, charnokite, and granite)

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Educational Applications and Inquiry explanation through any single pathway of inquiry (Ault, 1998; Frodeman, 1995). Inquiries How does one systematically inquire about in the earth sciences are not necessarily about the Earth? Fundamentally, geology is the study making generalizable statements that go beyond of (a) materials (such as rocks, minerals, water, a setting. They can, instead, consist of describ- etc.), (b) space (i.e., where the materials are ing an event that represents a setting and then found or how they are distributed), and (c) time comparing descriptions for different settings (i.e., how materials and their distributions have (Ault, 1998). The challenge is to frame these changed and evolved). An important consider- questions in terms of material, space, and time, ation in earth inquiries is that students should and then facilitate larger and longer term under- create “by [their] own effort an independent standings by promoting a broader signifi cance. assemblage of truth,” a point made by one of Geology as a science is dependent on time and the fathers of American geology, T.C. Cham- place (Toulmin, 1990), and earth inquiries are berlin (1897, p. 848). What becomes apparent fundamentally place bound. Only when consid- early in any earth inquiry is that questions are ered as components of an interdependent system often based on incomplete information about can one integrate inquiries into topics, such as Figure 6. A simple, circular rock cycle, as complex, interactive, and (ultimately) uncon- tectonic cycles and rock genesis, across loca- presented in many introductory geology trollable events, and thus, these questions defy tions and time (Kitts, 1977). texts.

suites that are not produced in modern tectonic cycles (Barker, 1979; Windley, 1995; Frost et al., 2006). In contrast, S-type, highly-alu- minous (and highly fractionated) granites are commonly produced today through melting of continental crust, but they are absent from Archean and most Proterozoic crust (Pitcher, 1979; Atherton and Tarney, 1979; Windley, 1995). Thus, fi eld evidence suggests that igne- ous rock associations have evolved through time, an important concept that is missing in the closed loop of the circular rock cycle. The Tectonic Rock Cycle is a more complex modifi cation of the traditional, circular rock cycle that incorporates rock evolution through time (Fichter, 1996, 1999b; Fig. 7). In Figure 7, we see in one diagram a fl ow chart of most of the processes that lead to the evolution of the physical earth. The path forms a question-mark shape, and it does not cycle back on itself com- pletely. Instead, beginning with a mafi c/ultra- mafi c parent rock, earth processes fractionate this material over and over, each time produc- ing a rock whose composition gets ever lower on Bowen’s Reaction Series (Bowen, 1912). Even sedimentary processes fractionate the rock’s chemistry. Observe that the sedimentary rocks in the yellow box, when metamorphosed Figure 7. Tectonic Rock Cycle (after Fichter, 1996, 1999b), which illustrates the intercon- (heated) to the melting state, result in an igne- nected pathways between rock types related to their genesis in a particular tectonic set- ous rock low on the reaction series. However, ting. A divergent boundary (Fig. 5, stages B–D) produces basalt and gabbro, leaving behind what is more important is that each stage of the ultramafi c residue in the mantle. Initiation of a volcanic arc system produces diorite/andes- Tectonic Rock Cycle relates directly with one ite in island arc settings (Fig. 5, stage E) and granite/rhyolite in continental arc settings or more stages in the heuristic Wilson Cycle (Fig. 5, stage G). Subduction and metamorphism of oceanic crust and lithic-rich sediments (Fig. 5). Thus, we have two interconnected produce blueschists and eclogites (Fig. 5, stages E and G). Mountain building along conti- heuristic models, often left unconnected in nental margins thickens the crust and produces Barrovian-style metamorphism of felsic introductory courses—a tectonic model (heu- sedimentary rocks, yielding slates, schists, and gneisses (Fig. 5, stages G–H). Tectonic stabi- ristic Wilson Cycle) linked stage for stage with lization enables extensive erosion of mountains that produces arkose, quartz sandstone, and the Tectonic Rock Cycle (Fig. 7). shales and carbonates in shallow seas (Fig. 5, stage I).

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Supercontinent Cycles and Diachroneity as continents as early continental crust (Windley, for choosing which rocks are important to teach Focal Points for Inquiry 1995). In the late Archean to early Proterozoic, by placing them in an earth systems framework many of these protocontinents assembled to where the relationships are more important than We highlight two important concepts that are form the cores (shield regions) of larger conti- the rocks themselves. lacking from many depictions of plate tectonics nents (such as Laurentia; Whitmeyer and Karl- The models are heuristic; we use the term in introductory earth science texts: (1) the cycli- strom, 2007). In turn, these larger continents “heuristic” to mean a simplifi cation that reduces cal, recurring nature of supercontinent assembly collided to form Rodinia (Li et al., 2007), and or limits inherently complex situations to their and breakup (e.g., there are more superconti- later Pangaea (Scotese and Sager, 1988), while basic components and explicates the basic ways nents than just Pangaea), and (2) the diachronous continually enlarging and modifying their mar- those components relate to each other. Once assembly of continental blocks into a supercon- gins. Thus, rocks created as juvenile, igneous the students come to understand how the com- tinent. Our approach is to address these instruc- arc material ultimately become ancient, stable ponents relate to each other, they can move on tional defi ciencies with animations of historical metamorphic rocks in the centers of present- to more real and likely more complex situations and modern supercontinent cycle concepts. A day continents. Through this process, rocks can and analyze them with the heuristic tool kit they simple animation of Wilson’s (1966) original spend millions of years at any of the stages of have developed. Through an understanding of map view of closing and reopening the Atlantic the heuristic Wilson Cycle (Fig. 5) or at any how these systems work, students can move Ocean (Animation 1) can be compared with a location on the Tectonic Rock Cycle (Fig. 7). By beyond memorization to actually thinking about modern interpretation of the relative movements focusing on the evolution of rocks in a variety of how the concepts can be applied to new situa- of major continents (Laurentia, Gondwana, and tectonic settings through time, the concepts of tions. Thus, study of the Earth becomes deduc- Baltica) and microcontinents (Avalonia and slow rates of geologic change through billions tive and predictive, not just inductive. Students Precordillera) throughout the Paleozoic that of years of the Earth’s history are reinforced in can deductively predict what kinds of rocks will preceded the assembly of Pangaea (Animation an integrated systems context. be generated under specifi c tectonic situations 2). By comparing and contrasting these two ani- and, more importantly, use rocks to determine mations, we fi nd that students intuitively get a No Rock Is Accidental ancient tectonic environments and processes. feel for the limitations of simple models of plate Students not only learn about the Earth, they tectonics, as compared with modern tectonic No rock is accidental, and every rock has a develop a scientifi c strategy for investigating the cycles that consider geometrical implications geologic story to tell. However, typically the Earth. and constraints of 3D plate motion. rocks we use as teaching examples, especially The incorporation of the assembly and in primary and middle schools, are the ones that Visualization-Focused Inquiry breakup of the ca. 900-Ma Rodinia supercon- are readily available in teaching collections. tinent (Animation 3) into the standard plate These collections commonly leave out rocks that Our use of animations to address the spa- tectonics curriculum encourages students to are abundant on Earth but not easily accessible. tial and temporal aspects of tectonic systems appreciate that there were predecessor super- For example, ocean lithospheric rocks (includ- prompts the question: what design features continents to Pangaea. Students should logically ing pillow basalts, peridotites, and serpentinites) should be incorporated to ensure that the deduce that supercontinent assembly is cyclic cover ~70% of the Earth’s surface but are often intended learning task is, in fact, accomplished? and make the connection that we are currently ignored because of their relative inaccessibility. Visualizations come in many forms—graph- within a transitional period between Pangaea However, they are abundant and important for a ics, illustrations, charts, and photographs. They and some future supercontinent. The Rodinia holistic understanding of how the earth system contain a complexity that derives from fi delity animation also demonstrates that superconti- works. to the reality or concepts that they attempt to nents assemble and break apart in stages. This Part of our goal in this paper is to fi nd a ratio- represent, with a level of abstraction associated can be further reinforced by a comparison with nal basis for deciding what should be taught, with their intended purpose. Holliday (1995) the Paleozoic Laurentia-Gondwana animation and what should be let go. As earth scientists, described a range of visualization types, includ- (Animation 2), where the smaller superconti- we work toward simple, ideal models, as is the ing those tied directly to textbooks, that (1) have nent of Gondwana forms in the early Paleozoic case in classical physics, where principles can affective value to students (spark interest, gen- and is separated from Laurentia by the Iapetus be clearly laid out and explored with mathemati- eral appeal to students, promote relevance), (2) ocean throughout the Paleozoic. Closure of the cal precision, independent of the messiness of promote positive learning behaviors (focusing Iapetus ocean and fi nal assembly of Pangaea the real world. The problem is, the Earth is not attention, facilitating remembering, rehearsal, occurs at the end of the Paleozoic, at least 200 simple, or neat, and our job as teachers is to help and reinforcement), or (3) have specifi c cogni- million years after early assembly of Africa, students grasp the world as it really is, with all its tive functions (summarization, compare/con- South America, Antarctica, and India as Gond- complexity. Geology does have its simple, ideal trast, portrayal of spatial relationships, and wana. Thus, the early Paleozoic assembly of models—the circular rock cycle, for example, understanding of scientifi c conventions). This Gondwana can be considered the fi rst phase in where rocks are transformed one into the other. approach equates specifi c features of visualiza- the assembly of Pangaea, followed in the later However, the circular rock cycle is rarely related tions with appropriate classroom applications, Paleozoic by the accretion of Laurentia and Bal- to generative tectonic conditions. This is not sur- indicating that images and animations need to tica to the Gondwanan core. prising, since plate tectonics is a subject with its be tailored to a specifi c educational objective. Another important feature of supercontinent own history, specialized techniques (e.g., grav- Further framing the categorization of visual- cycles is that ancient rocks and crustal compo- ity, magnetic, seismic studies), and vocabulary izations, Winn (1989) defi ned graphics used in nents are reused (and often reworked) in a vari- that largely arose out of oceanography and instruction by the (a) methods, or those strate- ety of tectonic settings through geologic time. geophysics, not out of geology. The integrated gies that activate specifi c cognitive processes, Rocks that formed in Archean island arcs (e.g., Wilson Cycles (Fig. 5) and Tectonic Rock (b) outcomes, or the tasks that are expected of TTG suites) later assembled into small proto- Cycles (Fig. 7) we present provide a rationale learners, and (c) the conditions, or the context

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and circumstances under which the instruction support, dense verbal components or explana- receive only superfi cial processing. To gauge the utilizing the graphics is to take place, inclu- tions—the animation is the intended voice. As level of processing, one must consider not only sive of learning modalities and aptitudes of the such, the tectonic animations and Wilson Cycle how the picture is to be used by the learner, but learners. Within the range of methods, Winn and Tectonic Rock Cycle diagrams presented in also the learner’s perception of the task to which describes grouping of concepts, labels and sym- this paper can be most effectively applied within the picture material has been assigned. Three bols, convention-based graphs, sequential rep- an inquiry-driven educational environment. Fol- positive interactions are required for a visualiza- resentations, hierarchies, and comparisons as lowing minimal introduction, students explore tion to have a desired effect (Fig. 8):

the means to make the abstract more concrete. the animations and diagrams and their implica- (a) Mp/T—the function and relevance of the pic- For our purposes, we wish to move learning tions prior to verbal discussion. Thus, the visual- ture to the task must be clear and relevant, away from traditional representations of the izations are primary, and the verbal component such that the picture can defi ne the task;

rock cycle, which are descriptive but abstract, is secondary. (b) Mp/Mt—the text and picture materials must and use the Wilson Cycle to tie rock-forming exhibit a mutual support and relevance for processes to particular places and times, adding The Effectiveness of Visualizations in interpretation, clarifi cation, and explana- predictive value based on plate tectonic theory. Education tion; and

In relation to the outcomes, or task expected of (c) Mp/L—there must be a facilitative role for learners, one needs to distinguish between the In considering the relative quality of visual- the picture in terms of attending, under- identifi cation of concepts, classifi cation of rel- izations in instructional settings, Weidenmann standing, and remembering by the learner. evant attributes of objects, sequences and pat- (1989) offered a cognitive model of evaluating When both text and pictures are used in the terns of elements, problem-solving informa- visualizations in their own right, rather than context of engaging student tasks, however, the tion, and mental modeling inputs. We desire strictly in support of text materials, consider- effect is decidedly positive on student learning for learners to understand that continents grow ing both text and visual materials in light of the (Pyle and Akins-Moffatt, 1999). Our approach over time and that an evolutionary perspective expectations on learners as well as the learners’ uses visualizations to focus on the learning on rock formation provides more learning value perceptions of the task to which the materials task of grasping three variables simultaneously than abstract descriptions alone can provide. (text or visual) are related. He defi nes four key (X-Y, position, and time), ultimately adding a With respect to the conditions, Winn describes elements—the Learner, the Task, the Text mate- fourth dimension—lithology. Thus, the task (T) the use of graphics in the supplantation of learn- rial (Mt), and the Picture material (Mp)—as presented to students using these visualizations ers’ prior or preexisting conceptual frameworks, context-defi ning instructional variables in which is to understand the multidimensional reality the activation and enhancement of learners’ both text and visualizations are considered of both the rock cycle and plate tectonics, as skills, and the formal modeling of implicit and simultaneously and independently. Weiden- opposed to the more typical disconnected pre- explicit relationships. Considering the predictive mann argues that most people assume that since sentation of these topics. In addition, the gen- value of the Wilson Cycle, desired skill activa- visualizations are a simple medium, then the eral mode by which a learner (L) is exposed to

tions and enhancements include the generation picture processing should only require (falsely) such content is through text (Mt), supported by of relevant questions, such as inquiring whether minimal cognitive effort. Thus, pictures tend to static visuals (i.e., reference pictures and maps). plates always separate, or must they sometimes converge. Collectively, these elements help to frame classifi cation taxonomies for both the description and application of science visualiza- tions as a function of instruction. Recent research on basic characteristics of illustrations in biology textbooks (Bowen and Roth, 2002; Pozzier and Roth, 2003) classifi ed visualizations on a scale refl ective of their con- crete or abstract natures. These classifi cations lead to taxonomies of visualizations, such as those in information design (Hansen, 1999; Wile- man, 1980), which provide information not only on concrete-abstract levels of representation, but also on specifi c indicators of audience response, perceptions of informativeness of specifi c types of visualizations, and evaluative frameworks for determining the impact of visualizations on learning. Through their descriptions and use of visual analogies, Issing et al. (1989) established the basis for the independence of visualizations apart from text materials in mediating the learn- ing process, such that visualizations can have a direct path to learning tasks in a context in which the text becomes adjunct to the visual- ization. Animations employed in this context Figure 8. Conceptual diagram of the relationships between learners, pictures, text, and the do not readily support, nor are they intended to learning task.

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To best represent reality, we focus on visualiza- systems. The realization that rocks and conti- Geology, v. 19, p. 598–601, doi: 10.1130/0091- 7613(1991)019<0598:PMOLAE>2.3.CO;2. tions (as Mp) to drive learning, with text serving nents, not just organic life forms, evolve over Dalziel, I.W.D., 1995, Earth before Pangea: Scientifi c Amer- in an adjunct role. In doing so, it is our belief time can provoke a powerful leap of cognition in ican, v. 280, p. 58–63. that the visualizations perform a stronger facili- a student toward an understanding of the Earth, Dalziel, I.W.D., 1997, Overview: Neoproterozoic-Paleo- zoic geography and tectonics: Review, hypothesis, tative role, showing space, time, and lithology its history, and its possible futures. The realiza- environmental speculations: Geological Society of in a manner that captures learner attention and tion that supercontinent cycles have evolved America Bulletin, v. 109, p. 16–42, doi: 10.1130/0016- 7606(1997)109<0016:ONPGAT>2.3.CO;2. encourages investigation beyond just “what” or over the past two billion years, and are an inte- Dennis, A.J., and Wright, J.E., 1997, The Carolina terrane “where,” to include “why” particular rocks form gral part of plate tectonic theory, should provoke in northwestern South Carolina, U.S.A.: Late Precam- in a particular place and time. students to ask the questions: “What will the brian-Cambrian deformation and metamorphism in a peri-Gondwanan oceanic arc: Tectonics, v. 16, p. 460– The task that we set for learners is to apply crust of our planet look like in the future?” and 473, doi: 10.1029/97TC00449. plate tectonic theory as a useful device in under- “What are the implications?” It is this level of Dewey, J.F., and Bird, J.M., 1970, Mountain belts and the standing the natural world. It is our contention student-initiated inquiry that we hope to reach new global tectonics: Journal of Geophysical Research, v. 75, p. 2625–2647. that the standard representations of tectonics as modern, geologically accurate visualizations Dickinson, W.R., 1971, Plate tectonic models of geosyn- and rock cycles in both texts and instruction, are developed for the integrated and realistically clines: Earth and Planetary Science Letters, v. 10, p. 165–174, doi: 10.1016/0012-821X(71)90002-1. particularly in pre-college settings, provides complex earth system and are used within sys- Dickinson, W.R., and Sucek, C.A., 1979, Plate tectonics only limited capacity for students to see plate tems-focused curricula. and sandstone compositions: American Association of tectonic theory in the same light as biological Petroleum Geologists Bulletin, v. 63, p. 2164–2182. 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Teaching, v. 39, p. 522–549, doi: 10.1002/tea.10035. chronology, paleogeographic settings and likely mod- MANUSCRIPT RECEIVED 6 FEBRUARY 2007 Kitts, D.B., 1977, The structure of geology: Dallas, Texas, ern analogues: Tectonophysics, v. 365, p. 283–299, REVISED MANUSCRIPT RECEIVED 2 SEPTEMBER 2007 Southern Methodist University. doi: 10.1016/S0040-1951(03)00026-X. MANUSCRIPT ACCEPTED 4 SEPTEMBER 2007

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