"ROUND ROCKS": TEACHING THE
PRINCIPLES OF EARTH
SCIENCE AND PALEONTOLOGY
SUPPOSE YOU are given one hour to tell someone about paleontology. The audience is
naive but interested. They want to know something about paleontology but have not
previously received, and may ever again receive, formal instruction in the subject. What will
you choose to talk about?
Will you choose to talk about local fossils, local geological history, how to collect fossils, or
the age of the Earth? Will you bring with you an assortment of fossils and tell your audience
what each one is? In other words, will you present a taste of the innumerable particulars in
which paleontology is so rich?
There are compelling reasons why you might do so. It is the particulars of paleontology the
beauty or diversity or complexity or antiquity of fossils that draw many students to the
field. Fossils are, aesthetic, and inherently interesting. Their variety and multiplicity appeal to
the collector in many people. Holding a fossil is exciting. Its age and direct connection to the
distant past lure us to name and know each individual specimen. "What is this?" is both the
most common and in many ways the most basic and important question anyone asks about a
fossil. Paleontology is a science rich in and heavily dependent on its data. Much of the value
of the fossil record lies in its particular "facts" Archaeopteryx is the oldest known bird;
trilobites are among the oldest known skeletonized metazoans; stalked crinoids are not as
common in shallow seas today as they apparently were in the Paleozoic; Seismosaurus is the
largest known land animal. Paleontological research relies on information such as this, and
the profession reveres and depends upon the specialists who can identify (almost) every
Devonian brachiopod or Jurassic or Eocene mammal tooth.
On the other hand, there are many reasons why you might choose otherwise. It has been
suggested that much of the decline in the popularity of paleontology at the college and
university level can be attributed to the way it was taught for decades (e.g., Linsley, 1970). A
distinguished professional paleontologist once told one of us that his undergraduate
paleontology lab exercises for the semester consisted of memorizing and drawing 2000
genera of fossil invertebrates. He said he was the only one in the class to go on in
paleontology. Emphasis on memorization may warm the hearts of some traditionalists, but it
does not appear to appeal to modern students. It also may not be the most effective way of
teaching what students really need to know. Paleontology today is decreasingly about being
able to identify large numbers of taxa in the field, and more about knowing what to do with
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The case may be even clearer outside of paleontology itself. What does an eighth or eleventh
grader in earth science need to learn? Assuming (as we clearly must) that the vast majority of
primary and secondary students will not become professional (or even avocational)
paleontologists, what information or experience will be of greatest benefit to them? What can
paleontology offer that other science fields cannot? What can paleontology say to students
that can make them more interested in science? Can paleontology teach principles or
processes of general science more effectively than other subjects?
The example of having only a single hour with an audience is not far from the situation many
paleontological educators confront. Whether as informal museum educators, occasional
speakers to classes or teacher workshops, or college professors of non-major science classes,
many paleontological educators have a very short period of contact to cover a given subject.
With all of these factors in mind, we find that a highly effective way of presenting
paleontology is to emphasize the thought processes that paleontologists use in their science.
These processes are not often articulated by practicing professionals, but they are in fact the
central questions of the discipline: How do we know that fossils were once alive? How do we
know that an object is a fossil? How do we know what kind of environment it lived in? How
do we know how old it is? These questions focus on how paleontologists do what they do.
They compel students to think about the process of scientific reasoning.
This realignment of focus may be distressing at first to those who find the specific results of
paleontological research so compelling and important. Emphasis on the techniques by which
paleontologists go about figuring things out necessarily de-emphasizes presentation of
particulars for their own sake; yet the particulars arise (just as they do in the practice of the
discipline) as the process of question-and-answer proceeds. This approach has important
benefits. It emphasizes what is in common between paleontology and other sciences. It
encourages a way of thinking that should be helpful to students in their other science courses
and eventually in their lives. This approach also demystifies paleontology, and by extension
the rest of science. It shows that science is accessible to all, that students can do science
themselves. It is not that scientists are smarter or have access to special truths that they
"know" that sea levels were higher in the Cretaceous, or that mammals evolved from reptiles,
or that horses arose first in North America. Scientists think these hypotheses are correct
because they have made observations, compared past to present, reasoned in a logical
manner, and allowed reference to the empirical world to guide conclusions that are always
ANY ROCK IN YOUR BACKYARD
We present this approach to paleontology and earth science in an exercise we call "round
rocks." The rocks we use are not necessarily round. Indeed, we stress (and we really do
mean) that it should be possible to carry out the process with literally any rock in your
backyard. The process consists of taking a rock in the hand and asking a single, simple
question: "How did this rock come to be this way?"
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We present this exercise to two categories of audience: students (at grades 6-12) and teachers
(K-12). Our one-hour presentations to students are intended to encourage them to begin to
think in a new way. Our presentations to teachers are intended to encourage them to teach in
a new way. During the main part of the exercise, we attempt to derive four basic principles. It
is our contention that application of these four principles alone can lead to the successful
interpretation of any geological hand specimen.
1) Physical law is constant in time and space. This is a necessary assumption of all
science, especially historical sciences (Gould, 1965, 1967, 1977). It is not testable; it is a tool
of reasoning required if we are to interpret the past. We cannot experiment or make direct
observations of processes in the past, but we can experiment and observe processes in the
present and assume that the physical laws, principles, and relationships (e.g., gravity, mass,
energy) that control the results also applied in the past. For example, moving water carries
sand today and we assume that it did so in the past in approximately the same way.
2) Apply the simplest processes first. This straightforward application of the
principle of parsimony is also a methodological tool, rather than an empirical generalization
(Gould, 1965, 1967, 1977). It says to not invoke hypothetical unknown processes or causes if
the observed results can be explained by presently observable processes. This does not
require that those presently observable processes were necessarily responsible for the
observed results; it is merely a starting point.
3) Propose testable hypotheses. Science is, at its core, the proposition of ideas that
can be referenced to the observable physical world. Not all hypotheses are testable with
observations. Such hypotheses are valid, just not very useful. Not all testable hypotheses are
correct. A hypothesis may be correct but not testable. It may be true; we'll just never know
whether it is. A useful and productive scientific hypothesis is one that readily yields
predictions that can be related to possible physical observations in nature. Although some
scientists and philosophers maintain that the most (or even the only) useful hypotheses are
those that can be falsified by one or more observations, others accept hypotheses that can be
merely supported by an increasing number of concordant observations. Gamma rays or
poisonous plants or trophy hunters may well have killed the dinosaurs; but it is difficult to
come up with physical observations that can either support or falsify these hypotheses.
4) Compare the results of present events and processes to the results of past events and
processes. We go to great lengths with both students and teachers to emphasize the
word compare and by the end of a class or workshop the word has often attained a mantra-
like quality. How do we know that a funny-shaped rock is a fossil? Compare it to organisms
alive today. How do we know that a fossil is a bone? Compare it to bones of living
organisms. How do we know that an orthicon nautiloid is related to modern chambered
nautilus? Compare the simple curved septa dividing the shells. How do we know that shale
was once mud? Compare the grain sizes. How do we know the temperature of a basaltic dike
at emplacement? Compare it to cooled lavas in Hawaii.
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Although literally any rock can be used for this exercise, we usually use rounded pieces of
sedimentary rocks that contain fossils (Figure 1). These specimens provide a great diversity
of historical phenomena and many processes that may be familiar from everyday life. The
rounding may in fact bring the story right up to the very instant the specimen was picked up
off of a beach or out of a stream and this may add a sense of immediacy or currency to the
Figure 2 shows an outline of the process through which we would take a group of teachers
with the specimen illustrated in Figure 1.
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First, we ask "What are the shapes in the rock?" How do we figure this out? We
compare them to shapes we may have seen before. We explicitly label the process as
comparison, and encourage participants to articulate the comparisons carefully. In the case of
most of the shapes in our illustrated specimen, they resemble in some respects living corals,
especially the mushroom coral Fungia (Figure 3). The search for what a shape in a rock
resembles may not be an easy one and may involve consultation of museum or teaching
collections and/or reference books of several sorts. The organism may well be extinct and
therefore unfamiliar to most participants. It may compare favorably in only one or a few
features with anything alive today. Although this is often frustrating, it is an excellent
example of how paleontology actually works. We have had good success using a spectrum of
fossil types, from the familiar and easily identifiable (e.g., clams, snails, corals, bones and
teeth) through the unfamiliar (crinoids, brachiopods, shelled cephalopods, trilobites) to the
downright weird (carpoids, conularids, tully monsters, tracks and trails). Once the idea of
comparison is introduced and applied to something "easy", participants gain confidence and
begin to take more risks and use more imagination.
If the comparison process has produced a consensus that the shapes are the remains of once
living things, then the question becomes "how did things that were once alive come to be
embedded in solid rock?" In our experience, a small number of teachers (and a larger
number of students, especially in younger grades) will try to envision some process whereby
a living thing was pressed into a solid rock. Most participants, however, will quickly grasp
that the rock must once have been soft, allowing the organic remains to become enclosed. It
is also useful to point out the characteristics of the rock itself (e.g., grain size, hardness,
color). What does it look like this rock is made of? Most sedimentary rocks have clearly
visible grains, bedding features, or sedimentary structures that should remind participants (via
comparison) of mud, sand, or gravel on a beach, river bank, or sidewalk.
If the fossil in the rock was once alive, in what type of environment did it live?
Reference to the habitat of its closest living relative is the place to start. This is readily
done with groups whose living representatives have narrow environmental preferences (e.g.,
exclusively marine corals, cephalopods, echinoderms; exclusively terrestrial horses,
elephants, land plants, land snails). In our experience, the principle is less easily
communicated to novices with groups that have a wide range of environmental preference
today (e.g., bivalves and gastropods) or with groups that are unfamiliar or extinct
(brachiopods, eurypterids). However, patient comparison combined with a few trips to the
encyclopedia for habitat information, can usually produce at least some hypotheses about
marine vs. freshwater vs. terrestrial. More comparison and research will yield more refined
How did the soft sediment become rock? We usually use the example of mudpies
and ask what happens if you squeeze wet mud or sand between your hands. When you open
your hands, the mud or sand stays together, at least for a while. Therefore, simple compaction
might lead to the formation of rocks from soft sediment. Analogy to how cement works can
then be used to introduce the idea of cementation between sediment grains as an additional
mechanism for rock formation.
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How did the rock get small? Did the soft sediment form just this little blob, isolated
in space? No, it probably started off as part of a much larger mass of rock, broke, and wore
down to what we hold in our hands. This may appear a trivial stage in the story, but it is not.
It is in fact the story of tectonics, uplift, and erosion. It is the opportunity to highlight that
most spectacular and significant of geological observations: the rocks at the tops of the
Himalayas contain marine fossils (Calder, 1972). Reference to processes observable today
indicates that deposition of sediments happens down (i.e., generally below sea level), whereas
erosion of sediments and rocks happens up (generally above sea level). Lithification
(compaction and cementation) happen even further down, below thousands of feet of piled-up
sediments. Thus, for a rock that formed through deposition, compaction and cementation to
become eroded requires that it was uplifted, perhaps thousands of feet. This statement carries
with it all the truly revolutionary implications of the history of geology changing positions
of land and sea, enormously long periods of time, and enormously powerful forces all
indicated by the rock in the palm of your hand.
Finally, why is the rock round? If the specimen at hand is round or even a bit worn,
there is the opportunity to close the story with a stage that may come right up to the present
moment. Do rocks break in round shapes? Common experience with bricks and cinder blocks
would suggest not. Thus the rock must once have had rough edges (produced by breakage as
part of the erosion discussed above), and become rounded by some subsequent process. If the
rock was found in a stream or on a beach or lake shore, then the actually processes that may
have produced the rounding may have been observable. The rock may have come from a
gravel pit, however, such as those excavated in glacial deposits. There is no longer an active
agent of rounding in such a setting and one must be hypothesized.
DOES IT WORK?
Many teachers tell us that the results of going through this exercise with students are
generally excellent. Students feel empowered to go and "do" earth science themselves. They
bring in rocks from their back yards. They ask more questions of their teachers. They focus
more on thinking like a scientist than memorizing lists of quickly forgettable facts.
Believing that we can reach more students by teaching teachers, we have made an operational
decision to focus increasingly on presenting the program to teachers. Yet success with
teachers themselves is harder to measure. Some teachers embrace the approach immediately
and report small but highly encouraging results. Others resist the approach from the outset.
They do so principally for one or more of the following reasons:
Complaint: "I don't know enough to guide my class through this exercise." Our response:
You know more than you think you do, and even if you don't, it shouldn't matter. Teachers
with at least one course in general geology should know enough about basic geological
processes to begin the exercise. For example: sedimentary rocks are made of mineral grains
(soft sediment) carried by water or wind and compressed or cemented together; older layers
of sediments are on the bottom; fossils were once alive; crystals grow; cross-cutting
relationships indicate a sequence of events. Any one of these notions is enough to start the
process of investigation. In our experience, a willing teacher can use the four principles listed
above, together with patience and a willingness to explore with their students, and achieve
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Complaint: "But what's the right answer?" Our response: It is of course useful to use rock
specimens about which a number of aspects are known in advance. But this is not necessary.
The teacher can and will probably know one or two facts about a given rock it is granite or
it has a fossil brachiopod in it or it came from the Grand Canyon. This is enough to get the
investigation going. Eventually it may be useful to consult a reference book or individual
more knowledgeable about the particulars. But if this is not possible, it can (and indeed
should) be emphasized that in many cases in "real" science there is no book or all-knowing
sage to consult for "real answers". If there were, we would not debate the origin of micrite,
the nature of the Ediacara fauna, the causes for iridium enrichments, the metabolism of
dinosaurs, or the ancestry of Homo habilis. We would just look up the answer. This is a vital
point of science that it is important to communicate to students.
Complaint: "I don't have time for this. I have to teach them _________ [fill in specific state
curricular standard or specific material]." Our response: Many states are now moving away
from specific lists of material to be learned in particular grades and toward more general
standards of skills such as critical thinking or problem solving. These outcomes are exactly
those that should result from the approach described here. If, however, specific material is the
overriding goal, we maintain that much of it can still be presented in a more investigative or
exploratory way than is often the case. Students can break up into groups with lists of
questions and one or more specimens and be asked to work with each other. The teacher can
list the material to be learned and then ask the student how this information might be derived
from actual specimens; how do we know?
Complaint: "If there's no right answer, how do I test them?" Our response: We see two
possible answers. Either test them the best way (i.e., essays), or use an approach similar to
that described here to help them learn the material. Test them the conventional way and hope
for an eventual transformation in testing philosophy.
There is a tension inherent in teaching science, one that is increasingly at or near the surface
amidst recent discussions. Science is fundamentally about the specific empirics of the natural
world, and yet all conclusions are provisional and uncertainty is essential and ubiquitous. Are
we then to teach details or the means by which those details are studied? Much current
literature in science education stresses the importance of principles over memorization (e.g.,
AAAS, 1993). Educators are constantly appalled, however, at the science illiteracy of their
students and the general public with regards to basic scientific facts. What is the answer?
It has been our experience with the exercise described here, that facts will emerge (and be
more likely to be assimilated) when they are presented in a way that appears to have
relevance beyond the specific information itself. "Round Rocks" attempts to demonstrate that
doing paleontology is no different from doing any other science; that paleontology (and by
implication all science) is accessible to teacher and student alike; and that once basic
principles and methods of science are learned, a never-ending stream of specifics can be
gathered and built into the familiar theories of textbooks and museum signage. We do not
argue, as comedian Tom Leher sang of the "new math" in the 1960's that " the important
thing is to understand what you are doing, rather than to get the right answer". Both are
important. We would paraphrase the old saying: Give a student a scientific fact, and they
learn for a day; teach a student where scientific facts come from and they learn for a lifetime.
AAAS (American Association for the Advancement of Science), 1993, Benchmarks for
science literacy. Oxford University Press, NY
Calder, N., 1972, The restless earth. Viking Press, NY
Gould, SJ., 1965, Is uniformitarianism necessary? American Journal of Science 263: 223-
Gould, SJ., 1967, Is uniformitarianism useful? Journal of Geological Education 15: 149-150.
Gould, SJ., 1977, Uniformity and catastrophe. pp. 147-152 in Ever since Darwin. W.W.
Linsley, R.M. 1970, Undergraduate paleontology in the liberal arts college: or "How many
thousand genera do they really need to know?" Proceeding of the Northern American
Paleontological Convention, vol.1, pp. 3-12, Allen Press, Lawrence, KS.
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