Temporal Learning Journal Club Findings
Marker at the beginning of the Trail of Time, Grand Canyon National Park. National Park Service photo.
This summary was compiled by Carol Ormand, Science Education Resource Center.
From January to May, 2011, the Temporal Learning Journal Club met once a month to explore the cognitive underpinnings of understanding geologic time by discussing readings from the geoscience and cognitive science literature. Our key findings from each meeting are summarized below.
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Themes from our first meeting, on temporal concepts and challenges:
- Humans struggle to grasp the immensity of Deep Time; the numbers involved are just plain difficult to comprehend. One strategy that appears to help is the use of logarithmic scaling. On the Trail of Time in the Grand Canyon, for example, visitors walk through history, with each meter of the trail being equivalent to one million years of Earth's history. However, the first million years are stretched out along the "Million Year Trail" to incorporate human time scales. Changes in the scale of time are marked, and assessment indicates that visitors are able to understand both the scaling and the changes in scaling. More generally, talking about events as having occurred "X times longer ago" than other events may help our students develop a better understanding of geologic time intervals. Similarly, building backward from the scale of human history to progressively longer time scales will help students to scaffold geologic time on to what they already know and understand.
- Research suggests that using key events is a natural way to scaffold understanding of difficult temporal concepts. Humans need anchors -- "landmarks" of some sort -- to subdivide the geologic time scale into memorable chunks. These anchors allow us to build a mental framework for geologic history. The anchors we use are often biological -- extinction events delineating the Ages -- but we can also incorporate the evolution of the atmosphere, oceans, and continents, the physical or geochemical evolution of Earth, and climate changes. Using more events, particularly for the earlier portions of Earth history, may help students to lengthen their perception of Deep Time. Building an understanding of how the Earth has changed through time (biologically, chemically, and physically) will help make the geologic time scale more meaningful.
- Understanding the geologic time scale requires a deep understanding of
- relative dating (sequencing of events), which depends on logical interpretations of the rock record;
- absolute dating (dating of events), which depends primarily on radiometric decay (at least for longer time scales) -- and these dates will change as new data become available;
- how geologists know what we know: What evidence do we see when we examine the rock record? How do we measure radiometric isotopes? How do we combine relative and absolute dating techniques with our observations of rocks to come up with a coherent story about the history of our planet?
- Understanding the rates of natural geologic processes is key to understanding how humans are affecting complex Earth systems, which is essential for making responsible decisions about our behavior and its impacts on the planet. For example, extinction is as much a process as it is an event; we are currently in the midst of a mass extinction "event," as well as a very rapid change in our climate. One of the most important lessons we can teach our students is that things that happen too slowly for them to observe on a day-to-day basis can nonetheless affect their lives profoundly.
Themes from our second meeting, on the cognitive processes essential to learning temporal geoscience concepts:
A conceptual representation of one, one thousand, one million, and one billion cubes. Click on the image to see a larger version.
- Experts have a well-developed mental geologic timeline, and we are adept at "zooming in" on some portion of it when that is relevant for our work -- that is, we have a nested hierarchy of multiple mental timelines. By helping our students to develop their own mental timelines, as well as the ability to zoom in, we can help them move from novice to expert temporal thinking strategies. Resources and strategies that may facilitate this kind of learning:
- Using a variety of time scales as a foundation (e.g. human time scale, life time scale, personal time scale), and progressively build toward working with longer time scales
- Visualizations, such as these (focusing on orders of magnitude in spatial dimensions):
- Movies that expand or contract our experience of time (the Matrix, Time Machine)
- Using narrative voice to describe geologic history: telling the story of the Earth
- Humans are wired to look for causal relationships; telling a causal story of events may help students to remember the sequence
- Field experiences
- In geology, we deal with both temporal and spatial dimensions that are orders of magnitude beyond our personal experience, and we routinely ask students to construct spatial analogies for Deep Time. We need to recognize the cognitive challenge of making an analogical mapping for something completely beyond human experience. Furthermore, mapping geologic time to a spatial scale may be difficult because we segment space and time differently: space in terms of features of an object or landscape, and time in terms of irregularly-spaced events (Resnick et al., in prep.). Our students might benefit from direct instruction on making this analogical mapping. Nonetheless, with such scaffolding, using spatial analogies for time is a strong strategy.
- We need to find ways to help our students understand geologically slow processes. As geoscientists, we think of our planet -- and all of its subsystems -- as dynamic, and we see static objects (such as rocks, minerals, and fossils) as recorders of that dynamic history. Our students see those same objects as static objects. We use these objects to infer the geologic history of the places they are found. Our students struggle to imagine that the landscape they see today has not always been there. We see the small-scale changes taking place on very short time scales as the source of large-scale changes that occur over very long time scales. Our students see small-scale changes taking place on very short time scales, but struggle to make the leap to large-scale changes that occur over very long time scales. Events are the building blocks of the geologic time scale. But in geology, "events" may stretch out over days, months, years, or longer time intervals (even to intervals longer than the human life span). It may be challenging for students to conceive of "events" that take years to unfold. What ties all of these examples together is a lack of understanding of the effects of very slow processes over very long time intervals.
Recommendations for using analogies to teach about geologic time, from our third meeting:
Geologic time mapped onto a 12-hour clock face.
- Articulate (at least for yourself, and possibly for your students) the learning goal(s) for using an analogy.
- Choose your analogies carefully (Jee et al.).
- Make explicit the mapping of the source to the target, and be explicit about where the analogy breaks down. A poorly chosen analogy can introduce or reinforce misconceptions.
- Start from the familiar (Jee et al.): an understanding of geologic time can be built from observable rates and timescales.
- For example, this can be done mathematically by calculating the length of time a processes has been operating from an observable rate and the scale of its impact over time. This could then be scaled up to the total impact of that process over geologic time assuming a constant rate. This could then be shown graphically on a timeline.
- This can also be done somewhat more qualitatively—by comparing slow rates of processes of change (such as erosion) with landscape evidence for profound geologic changes (such as canyons)—to conclude that Earth must be very, very old. Ideas for this come from the Pete Palmer/GSA video, "The Earth Has a History," and the story of Hutton by the sea.
- Don't focus entirely on visual analogies (Clary and Wandersee):
- Use handclapping: have students clap once to represent one year. Ask them to clap out the length of one student's life (one clap per second). Then ask them how long it would take to clap out the history of the Earth?
- Use walking: lay out a very long timeline (in terms of distance), and walk through Earth's history.
- Use contemplation: ask students to contemplate Deep Time, and create the space and time for them to do so.
- Engage students in analyzing analogies.
- Consider having students construct analogical mappings (map the source to the target) themselves. You will need to model the process of constructing a mapping. Once students understand the process of analogical mapping, making that mapping from source to target may help them to develop a deeper understanding of each analogy used in class.
- Consider having students (either individually or in groups) identify where specific analogies break down. This may lead to a deeper understanding of both the analogy and the target concept.
- When using physical timelines (including pencil-and-paper timelines) as analogies for geologic time:
- Make sure that the anchor points on the ends of the timeline are clear.
- Provide structured opportunities for students to compare timelines on different scales (Thompson and Opfer) and in particular to observe where and how far apart the same anchoring/landmark events are on the different scales.
- Make time intervals and scale changes on the timelines as predictable and regular as reasonably possible.
- Let students practice using scientific notation. This helps them to understand the relationships between powers of 10 and may expand the range over which they have a strong understanding of scale.
- Generate and use analogies about geological processes and "ways of thinking" as well as about geologic time itself.
- For example, constraining the age of the Cambrian-Precambrian boundary is like defining the timing of an event in your life by the ages of events that occurred before and after it.
- Robust analogies for teaching about radiometric dating and other difficult concepts are valuable.
Themes from our fourth meeting, on strategies for teaching about geologic time:
Cognitive challenges in learning and teaching about geologic time:
- It's difficult to extrapolate beyond one's own experiences and to think beyond a human time scale. This manifests itself in difficulty imagining processes we cannot observe directly, because of either the spatial or temporal scales involved (e.g. plate motion or the formation of an unconformity), difficulty imagining the long-term effects of everyday processes we can observe (e.g. erosion by flowing water), and difficulty imagining the cumulative effects of occasional catastrophes (such as plate motion associated with earthquakes). Students may even struggle with the fundamental idea that the Earth is constantly changing: that it is never, even momentarily, static.
- It's difficult to construct and use multiple different time scales. In its purest form, this requires synthesizing information from different locations and different scales, in your head. Even on paper, in the classroom, it requires correlating information from different sources.
- It's difficult to relate the geologic past to the present to the geologic future. In part, this may be because our knowledge of each is based on different tools. For instance, we learn about the past through crosscutting relationships, proxies, and radiometric dates; we learn about the present via observations, and we learn about the future by constructing models based on extrapolation and our understanding of geologic processes.
- The geologic past described by geologists is not intuitively obvious, even from a detailed observation of the current landscape and processes. Indeed, the current landscape is the cumulative effect of many different processes operating at many different time scales. Synthesizing those processes and their effects in real time is difficult even for experts.
- We do not currently have the tools to effectively assess student understanding of Deep Time.
We recommend the following teaching strategies, with the caveat that we have no assessment data on their effectiveness. These recommendations are based on our attempts to address the challenges enumerated above:
- Have students observe and compare modern geologic processes and ancient geologic deposits, preferably in close spatial proximity to each other (for ease of visual comparison).
- Use local/regional geology to construct an integrated timeline for an outcrop/area/region.
- Be explicit about using multiple time scales, and about how they relate to each other. Start with more familiar time spans and work up to longer periods of time.
- Use students' understanding of the interactions of continuous and catastrophic events within human history and in our own lifespans as a foundation for understanding how they interact over geologic time scales.
- Use spatial-temporal analogies. (See last month's notes for suggestions on teaching with analogies.)
- Explicitly articulate our thinking processes in the field, so that students understand that we are constantly evaluating hypotheses and making predictions from them and testing those predictions.
- Explicitly teach how geologists know what we know about the history of the Earth, particularly including geochronology.
- Employ the affective domain:
- Have students collect and research their own personal rock samples.
- Tell stories about where and when you (or your colleagues) collected the rock samples you use in your classroom.
- Use time-lapse photography
- Of physical models, such as a stream table
- Of natural processes, such as sediment transport or glacial movement (see, for example, http://earthvisioninstitute.org/extreme-ice-survey/
- But beware: in cognitive science experiments, people struggle to figure out sequence of events from animations – which suggests that students may still have a hard time imagining how static outcrops relate to dynamic processes, even if they've seen the dynamic process (via animation or time-lapse photography or ....).
Themes from our fifth meeting, on teaching temporal concepts in geoscience
The Takla Makan Desert is China's largest desert, situated in the middle of the Tarim Basin in Xinjiang Province. It is one of the largest 'shifting-sand' deserts in the world. The remains of ancient forests and riverbeds hide amidst the desert vistas. Satellite image courtesy of [link http://www.digitalglobe.com'DigitalGlobe'].
- We want our students to understand that geologic history is the complex intersection of processes occurring very slowly over extremely long periods of time and short, infrequent, high impact events. We also want them to grasp that the slow processes, which seem to have negligible effects on a human time scale, have profound effects over the course of Deep Time, and we would like them to be able to imagine how that is so. We recognize that our students' abilities to understand these slow rates and and the time scales over which they act constrain their ability to understand geologic processes and the landscapes formed by those processes.
- The extreme difference between human-observable time scales and Deep Time makes extrapolation a challenge. Geoscience experts have developed methods for dealing with this challenge, which we hope our students will also learn to apply:
- We use the Principle of Uniformitarianism to infer the rates of geologic processes in the distant past.
- We use the present-day landscape to substitute space for time: we search for regions of the planet that are affected by the same geologic processes but are in different stages of development. In many cases these regions are adjacent to each other.
- It is critically important for an informed citizenry to understand the difference between the rates (and effects) of natural geologic processes and the rates (and effects) of human activities, so that we can make intelligent choices about public policy issues. We are currently far from this ideal.
- Use the construction of the geologic timeline as a mechanism for discussing the relationship between high impact short events and gradualism.
- Make explicit the relationship between geologic events and the landscape in which they result.
- Consider teaching radiometric dating, so that students know how we know specific dates for ancient events. Delve into the nitty-gritty details of using multiple radiometric systems, closed vs. open systems, what it means when radiometric "dates" appear to be in conflict with each other, and error bars for dates/ages. Explore students' misconceptions about scientific uncertainty so that we can address those misconceptions directly.
- Find ways to teach the "space for time" substitution, including (but not limited to) Walther's Law. While this kind of interpretation is central to interpreting the stratigraphic record, it presents quite a challenge for most students.
- Move from the past to the present to implications for the future.
- Is it the case that the way we think about everyday events is going to be useful in designing instruction about very long times? Can we reason from analogy with the familiar when the scales are so different, or are we better off working from a symbolic representation of Deep Time?
- Would using geologic rates as a framework for a geoscience curriculum lead to a comprehensive grounding in geoscience or would some important concepts be lost? If it works, a side benefit would be the development of students' quantitative skills.