"Bookends" to 30 Years of Thinking about Teaching Geologic Time
Kip Ault, Professor Emeritus, Lewis & Clark College
The Present: Time as Place and Referee
Excerpt from a talk at the dedication of the Trail of Time, Grand Canyon National Park, 2010
The quest for a psychological appreciation of vast durations of time is a matter to postpone until after considering how geoscientists use time in argument and explanation. Among the most notable aspects of geologic reasoning are (a) strategies that substitute place for time in order to achieve explanatory aims and (b) arguments that depend upon time relationships in order to referee among competing hypotheses. Getting the order in time right is, therefore, a key criterion of persuasive argument; appreciating duration is a different matter.
The assumption of vast duration, even without psychological appreciation, provides a basis for trusting a basic principle of geologic reasoning: substituting place for time. Processes that go on for long periods of time—and processes that start and stop at very different times while unfolding at wildly variable rates—leave records. The accumulation of these records is referred to as "the present" and such records vary from place to place. The present geology and topography of the earth, whether resulting from tectonic or erosive forces, volcanism or sedimentation, in a very real sense is "the interference pattern between differently scaled processes" (Allen & Hoekstra, 1992).
The present is the key to the past not only because the landscape is an interference pattern to decipher but also because present time represents a sampling distribution of the results of past processes. Characterizing geologic patterns and processes observed in present time as a sampling distribution of past (and future) ones enables extrapolations of geologic processes. One place may stand as an example of a past stage, another as an even more ancient pattern for some present process. Extrapolating possible futures depends upon treating the present as a sampling distribution—with some places serving as examples of the future states of other places. Often such reasoning makes use of places as "modern analogues."
Substituting place for time does entail a risk of circular reasoning. Determining the order of events in time must have independence from putting events in a causal sequence of stages. Historical stages are hypothesized according to some explanatory principle (Gould, 1986, "Evolution and the Triumph of Homology, or Why History Matters, American Scientist, 74, 60-69). For example, Cascade stratovolcanoes might be presumed symmetrical and conical in a youthful stage, then broken and craggy in a later stage, the consequence of eruptive and erosive processes. If this arrangement in stages were exploited to determine relative ages, a craggy volcano would be labeled "old." However, using the stages to infer order in time is circular. The craggy volcano might be found to be youngest of all and a symmetrical one by far the oldest within a continuous range. Black Butte, near Bend, stands as an example of an old, conically symmetric volcano that apparently escaped Pleistocene glaciations. Mt. St. Helens is a very young, now quite craggy one because one of its slopes failed catastrophically in 1980. There do seem to be stages in the development of Cascade volcanoes, but getting these in proper order and recognizing the exceptions depends upon determining order in time independently.
The challenge to think on different scales permeates geologic reasoning because coherence in time characterizes good geologic explanation. As scales change—from mineral fabric to regional lineations, from explosive rapidity to gradual transformation—problems shift. Samplings of processes, if arranged as reliable stages, must be done on proper scales—but to know the proper scales to sample, much must be known about the process.
Hence do geoscientists use the concept of time to reason about geologic events: time as place and time as referee. Both place and referee are related to concepts of stages and sampling distributions; both represent a response to the fundamental challenge of scale to geologic reasoning. This conception of the logic of geologic time is distinct from the notion of appreciating time's vastness. This logic of time—as place and referee—ought to guide teaching in the context of solving geologic problems even for novices. Events cohere in time—in sequence and synchrony—or things must have happened otherwise; time ultimately referees among competing theories of geologic processes that substitute place for time.
Geoscientists not only know time's vastness, they reason with the logic of time as arbiter and they treat the present as a sampling distribution of events through time. The tools of geologic reasoning respond to the distinctive demands of solving temporal problems on scales inaccessible to human lifetimes. How geoscientists use time in the context of solving particular problems ought to guide, in substantial measure, what to teach novices in order to introduce the subject in an accessible, inviting, and authentic fashion.
The Past: Abstract to
Children's Concepts About Time No Barrier to Understanding the Geologic Past
Ph.D. dissertation, Cornell University, 1980
The purpose of this study was to describe the diversity and range in the elementary grades of children's concepts about time and to compare children's understanding of time to the functioning of time in geologic explanations. In order to make this comparison, an analysis of the structure of knowledge about geological time was undertaken. Children's understanding of time was probed using an informal clinical interview style. The relational view of time was judged an appropriate philosophical starting point for examining concepts about time both in science and children's understanding. Forty children, ten per grade level from grades K, 2, 4, and 6, were interviewed in response to a series of time-concept tasks. Analysis of the transcribed interviews revealed that children in kindergarten and grade two tended to equate more time with more distance, speed or effort. Not until the fourth grade interviews were any subjects encountered who could apply the principle of time conservation as a logical predictor of "return" time when the observed motions were reversed.
Responses to questions about the passing of time and its measurement with series of sounds indicated some understanding of the principle of equal intervals as early as second grade. Many children were categorized as "clock-bound" -- as holding the notion that time exists as something real and absolute, that its discovery was accomplished by the people who first "found out" that time goes by in seconds, minutes, and hours.
Several children were comfortable speaking of durations as the number of reference events an activity took, ranking series of physical events as good or bad for time measurement, and deriving a standard unit from seemingly irregular sound and sight sequences. The successes and frustrations the children had with these activities indicated a very elemental association between time and counting.
Children's apparently illogical statements about time were most often viewed as evidence of their reinterpretation of a problem consistent with their own meanings for the words used in the question or their familiarity with the observable cues in the context of a task.
In general, the results of this research do not support a Piagetian model of development nor stage theory implications for curriculum planning. The responses demonstrated that children in the upper elementary grades can and do conceptualize time in a manner indistinguishable from its use in geologic explanations. An understanding of time derives meaning through an increasing power to coordinate relations among the occurrences of physical events.
The simultaneities, synchronies, and references to "clocked" durations in geologic inquiry usually refer to events children feel no need to order conceptually. Nevertheless, these elementary concepts about time are ones children use effectively in reference to familiar experiences. Using core samples from a layered compost pile, children in this study could make relative age deductions with logic analogous to that for correlating Devonian rock strata in the local region.
The teaching of geology ought to link each element of time conceptualization -- succession, before and after, simultaneous endpoints, number of X for Y to happen, definition of a standard unit, repeatable set of reference events, deduction of sequence and duration -- to specific geologic records and events. As an intermediate step, how a geologist uses time can be tied to the interpretation of experiences available to elementary school children.