College Student Conceptions of Geological Time and the
Disconnect Between Ordering and Scale
Julie C. Libarkin
Department of Geological Sciences and Division Science and Mathematics
Education, Michigan State University, 206 Natural Sciences Bldg, East Lansing,
MI 48824
Josepha P. Kurdziel
Department of Ecology & Evolutionary Biology, University of Michigan 830 N.
University Ave., Kraus Natural Sciences Bldg., Ann Arbor, MI 48109-1048,
josephak@umich.edu
Steven W. Anderson
MAST Institute, University of Northern Colorado, Greeley, CO 80639
steven.anderson@unco.edu
ABSTRACT
College student conceptions of the scale of geologic time
and the relationships between time and geological or
biological events were evaluated through interviews,
open-ended questionnaires, and student generated
timelines collected from four institutions. Our data
indicate students hold a number of alternative
conceptions about the Earth's formation and the
appearance of life, and these ideas are remarkably
consistent across institutions. Transferability of these
findings was evaluated via comparison with Geoscience
Concept Inventory questions related to geologic time
collected from 43 institutions nationwide. Detailed
evaluation of student timelines reveals a notable
disconnect between the relative relationships between
the age of the Earth, the time required for the origin of the
first life forms (prokaryotes), and the evolution of
dinosaurs and humans. Students generally placed these
events in the correct relative order, but had a poor
understanding of the scale of time between events.
Intriguingly, timelines can be mapped onto ternary
diagrams, and the relationship between ternary diagram
zoning and specific ideas of geologic time is explored.
We found that some students, for example those with a
young Earth perspective, map onto specific conceptual
zones on ternary diagrams.
INTRODUCTION
Student understanding of geologic time has been
explored in a variety of settings, including elementary
(Ault, 1982; Schoon, 1992), high school (Marques and
Thompson, 1997; Oversby, 1996; Schoon, 1992), college
(DeLaughter et al., 1998; Libarkin et al., 2005; Schoon,
1992), pre-service (Gosselin and Macklem-Hurst, 2002)
and in-service teacher (Trend, 2001; Dahl et al., 2005)
populations. Researchers have focused on both relative
(Trend, 1998; Trend, 2000; Trend, 2001; Dodick and
Orion, 2003) and absolute time (Libarkin et al., 2005;
DeLaughter et al., 1998; Trend, 2001), and some work
shows intriguing relationships between relative
positioning of geologic events and understanding of
absolute geologic time (e.g., Trend, 2001; Dodick and
Orion, 2003; Libarkin et al., 2005). Researchers generally
find that students are more comfortable with relative
time than absolute ages (Trend, 2001), although these
same students may have a poor understanding of
absolute ages (Libarkin et al., 2005). In addition, young
children tend to have a difficult time extracting analogies
about relative ages to relative age dating of geologic
strata in general (Ault, 1982).
Trend (1998; 2000; 2001) and Dahl et al. (2005) have
conducted detailed studies of children, pre-service and
in-service educators' ideas about and interest in geologic
time. These works employ a similar event-ordering task
that requires participants to consider when various
events happened in Earth's history, and more
specifically, the relative order of geologic events. Events
are both biological and physical in nature, and may
include the appearance of birds, the opening of the
Atlantic Ocean, the appearance of life and the formation
of the planet Earth. In general, participants seem to be
familiar with the general relative order of biologic events
in Earth's history, although geologic events, such as the
opening of the Atlantic, do not seem to have a significant
place in student or teacher ideas of the Earth through
time (Trend, 2001). Trend (2001) suggests that this may
be the result of the attention paid to biologic events
throughout the K-12 curriculum. In addition, several
researchers have observed that participants of all ages,
ranging from elementary-aged students to in-service
teachers, believe that Earth and life originated at the
same time (Marques and Thompson, 1997; Trend, 2001;
Libarkin et al., 2005).
In addition to fundamental research into student
conceptions, significant energy has been put into
considering the difficulties students have understanding
geologic time, as well as crafting curricular materials that
can facilitate instruction. For example, the January 2001
issue of the Journal of Geoscience Education contains a
series of papers focusing on the teaching of geologic, or
deep, time. Certainly, development and testing of
curricula designed to impact student conceptions of
geologic time has a long history in geoscience education.
Curriculum developers often attempt to correlate
geologic time with either human time scales, such as a
person's life, or convert geologic time to spatial scales
that can be observed in a typical classroom. For example,
many teachers use a string to represent geologic time,
and have students mark various significant geologic
events, like the appearance of multi-celled organisms,
along this spatial scale. Richardson (2000) suggests that
this string could simultaneously be used to represent a
student's lifetime, allowing for a relative comparison of
events through time. The hope is that this lifetime vs.
geologic time evaluation will help students understand
the relative recentness of many geologic events, such as
the extinction of the dinosaurs. In a more thorough
discussion of a similar geologic time exercise, Hermann
and Lewis (2004) discuss an extended three-week
exercise designed to link the geologic time scale with a
time scale of a relative's life. Hermann and Lewis (2004)
advocate for formative evaluation of student work, and
in particular argue that teachers should modify their
own instruction based upon student input, and this is
Libarkin et al. - College Student Conceptions of Geological Time
413
Figure 1. Questionnaire prompting students to place geologic events along a timeline. The interview protocol
followed a similar line of questioning.
Figure 1). These data were collected during the middle to
end of the semester from students enrolled in entry-level
biology and geology courses. Qualitative results from
these and other data have been discussed previously in
Libarkin et al. (2005). We report here on a specific
component of the interviews related to creation of a
geologic timeline. Students were prompted to complete a
timeline by placing four events between Earth's
formation and the present: The first appearance of life on
Earth, the appearance of dinosaurs, the disappearance of
dinosaurs, and the appearance of humans. These events
are labeled FIRST LIFE, DINOS, NO DINOS, and MAN
on timelines, respectively. Students were given the
freedom to interpret the meaning of these events for
themselves and were prompted to explain their
responses. For example, while terrestrial, four-legged
dinosaurs went extinct at the end of the Cretaceous, a
lineage of dinosaurs gave rise to modern birds. We
allowed students to explain their reasoning either
verbally or in writing if they believed dinosaurs still
METHODS
existed. Students were also asked to provide absolute
College student conceptions were probed in interviews numbers for the occurrence of these events, and to
(n=15) and through open-ended questionnaires (n=49; provide written responses to several questions related to
geologic time. Finally, timeline data were collected over
particularly important for difficult subjects like geologic
time. Hermann and Lewis' (2004) instructional approach
is in agreement with the well-established conceptual
change theory of educational practice (e.g., Posner et al.,
1982).
This study attempts to expand upon existing
research about geologic time by documenting college
student ideas about geologic time and how we can use
these ideas to develop effective curricula. We build upon
existing techniques, particularly interviews and a
modified event-ordering task, to collect student ideas
about time, the relative occurrence of geologic events,
and absolute ages. This study presents a simplified
approach to gathering student conceptions of geologic
time (e.g., Trend, 2001), and applies a new analytical
technique that has significant potential for evaluating
complex models of, as well as the impact of belief
systems on, student ideas.
414
Journal of Geoscience Education, v. 55, n. 5, November, 2007, p. 413-422
Figure 2. Representative student timelines (after Libarkin and Anderson, in press). A) Student indicates
absolute dates and relative positioning of events that are close to the scientific model. The words “Permian
extinction? 50 mya? Not sure” appear next to NO DINOS [Disappearance of dinosaurs] on the original
drawing. This timeline plots very close to the accepted scientific model on both linear and ternary diagrams.
B) A blend of scientific and non-scientific ideas. This timeline indicates that life existed when the Earth first
formed. C) Creationist perspective of Earth’s history and occurrence of events. This student plots in the
young Earth conceptual zone in Figure 5.
several years (2002-2004) during data collection for a
larger study, and interview and questionnaire protocols
changed over time. Although interview prompts and
questionnaires related to geologic time were identical
across this study, some timelines contained gridlines
while others did not (e.g., Figure 2). Comparison of
timelines created on gridded and non-gridded paper
showed no difference between either student ordering of
events or the spacing of events. In effect, the range of
timelines observed in this study was present on both
types of paper. We concluded that no difference exists
between student timelines completed on gridded versus
non-gridded paper, and thus we combined the two
datasets into the single one discussed here.
Study Population - Students (n=63) from four U.S.
institutions, a small elite private university in the
northeast (A), two large state universities located in the
southwest (B) and east (C) and one small public liberal
arts college in the Midwest (D), participated in this study.
Questionnaires were completed by students enrolled in a
general education biology course at B (n=29) and an
Honors College natural science field course at C (n=19).
Timelines were collected during interviews with
introductory geology students at A (n=5) and D (n=10).
One student from A provided two alternative timelines,
both of which are included here; hence, 64 timelines were
analyzed. Demographic data were available for the 44
students from A, B, and D. Participants were
overwhelmingly Caucasian (86%; one student
abstaining), with four Hispanic, one Asian, and one
student
of
mixed
Asian-Caucasian
ethnicity
participating. In terms of gender and age, 61% of the
participants were female, and most were between 18-25
years old, except for six students who were 26-55 years of
age. Most students reported having exposure to biology
or earth science in high school. Three students were
majoring in science or engineering, specifically
environmental science, meteorology, and electrical
engineering. The remaining participants were all
Libarkin et al. - College Student Conceptions of Geological Time
415
Type of Validity or Reliability
Transferability
Dependability
Confirmability
Explanation of Validity and Reliability*
Approach in this Study
Are the research findings significant in other contexts? All study variables need to be
defined so that future researchers can make reasonable assumptions about applicability
to other settings.
Comparison of GCI results to timeline results from this study indicates that findings from the
timeline portion of this study have application in other instructional settings.
Is the study repeatable, are findings stable over time, and do different measures of the
same trait yield similar results? "A careful review of the process of data collection and the
research product, especially as time evolves, can help establish reliability. For instance,
"comparison of observations carried out by two different researchers, as well as their
analyses, can help determine the dependability of the qualitative process and study
conclusions." (Libarkin and Kurdziel, 2002). Inter-rater reliability is one approach that
can be used to gauge agreement between researchers.
Inter-rater reliability: Two people measured student placement of events for a subset of
timelines (n=10) and were in agreement within 5% for every measurement.
Are study findings independent of the researcher's own personal biases, and therefore
objective? Would another researcher reviewing the process of interpretation come to the
same conclusion?
This is difficult to evaluate, although all three authors were in agreement with the conclusions
published here. The methodology is well-documented, allowing for confirmation of these
findings by future researchers.
Note: Not all aspects of qualitative validity and reliability were evaluated in this study. *Explanations are partially summarized from
Lincoln and Guba (1985) and Trochim (2004).
Table 1. Validity and Reliability (or Trustworthiness) for this Study
non-natural science majors enrolled in diverse fields
including creative arts, business, communication,
psychology, elementary education, and management
information systems.
Interviews were transcribed
verbatim from audiotapes.
Analytical Methodology - Students provided absolute
numbers for occurrence of events, relative placement of
events on the timeline, and written or verbal
explanations of their responses. Student ideas about the
Earth's formation, the relationship between appearance
of life and extinction events, and absolute ages of events
were collected and grouped into categories via standard
content analysis. The relative placement of events on
timelines was investigated, as well as the spacing
between events. The placement of three events, the
appearance of life relative to Earth's formation and the
disappearance of dinosaurs relative to the appearance of
humans, was used as an example for evaluating student
ideas about the scale of geologic time. Through analysis
of the relative spacing of these events we were able to
specifically consider those students who believed life
existed when the Earth first formed as well as those
students who indicated that humans and dinosaurs
co-existed.
Quantitative analysis of timeline data was
conducted to ascertain the significance of the relative
placement of all events along the timeline. Timelines
were converted to ordinal scales, where "Earth Forms" =
0 and "Today" = 1.0. Relative positions of two of the four
events were plotted on simple x-y graphs and simple
regression analysis was performed. Comparison of the
position of all events was conducted, although only the
most significant results are discussed here.
Events were also plotted on ternary diagrams to
evaluate any zoning in event placement. All time-lines
were first normalized with respect to total time (e.g. total
time on each timeline was set to 1, or 100%, as describe in
416
the paragraph above). The percentage of total time is
determined for three time steps of interest (for example,
the time between 1) EARTH FORMS and FIRST LIFE, 2)
FIRST LIFE and MAN, and 3) MAN and TODAY). Those
three percentages for a single timeline are then plotted on
a ternary diagram as a single point. Zoning of responses
on these ternary diagrams was evaluated with a focus on
specific subgroups, such as students with a "young
Earth" perspective, and comparison with the student
population overall.
Validity and Reliability - This study utilizes qualitative
data, so measures of qualitative validity and reliability
(sometimes together called 'trustworthiness') are
discussed here. In particular, we address measures to
ensure transferability, dependability, and confirmability
(Lincoln and Guba, 1985; Trochim, 2004; Table 1).
Transferability deals with the question of whether or not
research findings will be significant in other contexts,
such as at other institutions or for a different population
of students. It is particularly important that the
demographics of the study population and other
variables be well defined, to allow future researchers to
ascertain the applicability of this study to future work.
Dependability in the context of this study refers to
whether or not the research is repeatable as well as the
agreement between our findings and outcomes of similar
research. Future researchers will be able to repeat this
study only if the data collection and analytical
methodologies are carefully defined, as has been
provided above. In addition, agreement between
researchers analyzing a single data set, called inter-rater
reliability, provides some sense of the repeatability of a
study. Finally, confirmability implies that findings are as
objective as possible, and that any unbiased researcher
would reach the same conclusions.
Journal of Geoscience Education, v. 55, n. 5, November, 2007, p. 413-422
EARTH'S APPEARANCE
AT FORMATION
Molten or gaseous
Desolate or featureless
Pristine or undisturbed
Different from today,
without explicit description
of differences
PRESENCE OF LIFE AT
EARTH'S FORMATION
Life did not exist
Simple organisms
Plants
Complex organisms
All organisms (may exclude
or include humans)
REPRESENTATIVE STUDENT QUOTES
"The earth was liquid lava when it was formed"
"very different-very hot, lots of gases, reducing atmosphere"
The Earth would have been "mountainless, oceanless [and with] no biomass" or "very
desolate…pretty much a big rock" or "barren [with a] different atmosphere, [and] no life"
"The earth would be more rugged. Shapper [sic] mountain peaks, rougher terrain"
"I believe the earth would be very similar to now-with the exception of what it looked like
b/f the flood…(I cannot put limits on God)."
"God created this earth that we live on and gave it the ability to form into something
different. I believe the world was different because of Plate tectonics."
REPRESENTATIVE STUDENT QUOTES
"the earth [at formation] is not fully developed enough to sustain life".
Life would not have existed because "the atmosphere was not yet formed and there was no
water yet"
"bacteria"
"There would be little life. Nothing would have been very diverse and complex. Animal
evolution began after the cambrian [sic] explosion."
"there would be bacteria, maybe some plants and one-celled organisms"
"there was the vegetation. There was lots of vegetation- lush, green"
"there would be living things, but probably less and not like the ones today. I think the
organisms I'd encounter would be things like fish, cockroaches…"
"…in Genesis it says that God created all living things-plants, animals &
humans…Dinosaurs which became extinct".
Table 2. Student ideas about life and the Earth at the time of the Earth’s formation
Transferability - Data from this study have been
compared to Geoscience Concept Inventory (GCI;
Libarkin and Anderson, 2005; Libarkin and Anderson,
2006; Libarkin and Anderson, in press) results collected
from 3845 students enrolled in 59 courses at 43
institutions nationwide. The GCI is a valid and reliable
multiple choice concept test designed for use in
geoscience classrooms. In particular, response
frequencies for two questions related to the age of the
Earth and geologic time are discussed here and
compared to timeline results (Figure 1). This allows us to
compare the small population included in our timeline
study to the population of students taking entry-level
courses nationwide. In general, timeline data and GCI
data are in agreement although important differences
that impact transferability of our findings do exist.
Details of the relationship between this study and GCI
data are discussed below.
Dependability - A complete description of the data
collection and analytical approach have been provided
above, allowing for future researchers to evaluate the
repeatability of this study for similar and other study
populations. In addition, inter-rater reliability, the
agreement of different researchers in their analysis of
qualitative data sets, was evaluated with respect to the
relative measurement of events placed on student
timelines. Two people measured student events along a
subset of timelines (n=10) and were in agreement within
5% for every measurement.
Confirmability - Although difficult to evaluate, the level
of agreement between all authors in development of
study findings is an important gauge of the objectivity of
a study. After discussion of the data and study
conclusions, all three authors were in strong agreement
with the findings presented here, as well as the
implications. The analytical methodology is also well
documented, allowing for confirmation of these findings
by future researchers.
RESULTS
Student timelines represented a wide variety of ideas
about Earth's formation and mechanisms for the origin
and evolution of life on Earth (Figure 2). Student ideas
ranged from strict creationist to the scientific, and
incorporated a wide range of alternative conceptions
about the Earth's formation and life on Earth that can be
categorized into major groups (Table 2).
Students had a range of ideas about the age of the
Earth, although most believed the earth was quite old.
70% (n=44) of students self-reported that the Earth is
billions of years old, with 57% (n=25) of these students
assigning an age between 4 billion and 5 billion years.
Seven students assigned ages between 4 million and 800,
one student described the Earth as "trillions of years old",
and six students reported the age of the Earth as 500,000
years old or less. The remaining three students did not
assign an age to the Earth, although they used language
in their timelines that suggested a young Earth
perspective, such as "God lives" and "Creation of the
Earth as described in the Bible".
Six students indicated that dinosaurs and humans
coexisted by placing the appearance of humans before
the disappearance of dinosaurs. This idea was only
observed among students enrolled at B and D, and
existed along with a wide range of ideas about the age of
the Earth. Students with conceptions of the Earth's age of
10,000 years, 4000-6000 years ("2000-4000 BC"), and 2100
years ("100 B.C.") held the co-existence perspective. The
Libarkin et al. - College Student Conceptions of Geological Time
417
Figure 3. Graph of relative positioning of two events,
appearance of first life and of dinosaurs, on student
timelines. The black square corresponds to the
scientific model. Other symbols are for each of four
schools as shown in the legend. Students falling along
the black diagonal line believe that life and dinosaurs
appeared at the same time in Earth’s history. Open
symbols are those students who indicated a belief
that the earth is 500,000 years old or less (n=6) plus
three students who wrote “God lives”, “When man
first migrated to the American continents” and “As in
Bible” on their timelines.
first student's timeline depicts seven days and a flood,
with "light" and the appearance of life on Day 1,
"animals, reptiles (dino)" on Day 5, and humans on Day
6. The Flood "wiped out most life", although dinosaurs
continued to exist until "2000 B.C.E.". The second student
indicated that all life existed at "creation", and that the
"flood" was related to the disappearance of the
dinosaurs. The student who believed the Earth formed
2100 years ago held an interesting multifaceted view. For
example, this student indicated that life existed when the
Earth first formed and that evolution requires time. In
particular, "there would be living organisms, such as
plants and insects. There would not be many because the
earth has just formed and nothing has had a chance to
evolve." At the same time, this student explained that
traveling to the time when dinosaurs were still alive
would require "travel to the years befor [sic] Christ
lived", implying a creationist perspective of Earth's
formation.
The remaining three students indicated that the
Earth ranged in age from 200 million to five billion years
old. One student (Earth age of 200 million years) held a
complex idea where dinosaurs actually appeared before
first life, and dinosaurs and humans co-existed, with
dinosaurs disappearing at "1 million years past man".
The remaining two students described the Earth as 4 and
5 billion years old. The first student indicated that
humans appeared slightly before dinosaurs and this
co-existence, according to the student's scale, lasted for
almost a billion years. The second student held a number
of scientific ideas in addition to the belief that dinosaurs
and humans co-existed. For example, the student
explained that when the Earth formed "There would be
no living things because earth was too hot at this time".
This student also indicated that life first appeared ~3.8
billion years ago, writing, "I remember that the oldest
fossil dates back this far". This student also recognized
418
Figure 4. Graph of relative positioning of two events,
disappearance of dinosaurs and appearance of man,
on student timelines. Symbols as in Figure 3. Data
below the solid line are those students who believe
that dinosaurs and man co-existed. Dashed line is a
polynomial linear regression through data from C
students.
that scientists age date features at the Earth's surface "by
radioactive decay".
Seven students in this study were unique in that they
marked all events except for the disappearance of
dinosaurs on their timelines. Two of these students
indicated that dinosaurs do not exist today, but simply
failed to mark NO DINOS on the timelines. One of these
students marked "Big Bang Theory" which from the
interview transcript appears to correspond to dinosaur
extinction, "Supposedly there are these theories about
the big bang theory, and that's when they ceased to exist.
There's lots of theories. Nothing is like a for sure deal. So
how long ago? I'll just write big bang theory". Remaining
students suggested that dinosaurs do exist today,
usually in the form of crocodiles or other reptiles. For
example, one student, the same one who marked "God
lives" and had no events marked on his timeline,
expressed this conception by writing, "Crocodiles are
dinosaurs still living today". Another student recognized
that birds are dinosaurs while simultaneously holding
an alternative conception that "there are dinosaurs living
today-crocodiles, alligators and some think birds are
descendants".
Normalization of Student Timelines - In addition to
qualitative evaluation of student ideas of geologic time,
student timelines were evaluated through analysis of
relative positioning of events on timelines. As described
in the methods, timelines were normalized to identical
scales, and the position of events was recorded relative to
the Earth's formation and the present day. These student
data were compared to scientifically- accepted values,
and across institution and student demographic data. In
general, a wide distribution of event positioning was
observed, and this distribution, although independent of
student demographics, was sometimes related to
institution.
The correlation between placements of two events
on student timelines indicates both qualitative and
quantitative relationships that are either not as obvious
or not evident through simple content analysis of
timelines. For example, comparison of the origin of life
Journal of Geoscience Education, v. 55, n. 5, November, 2007, p. 413-422
Figure 5. Ternary diagram of spacing between four
events on student timelines. Axes correspond to
spacing between Earth’s formation and Appearance of
first life (EARTH FORMS-FIRST LIFE), Appearance of
first life and Appearance of humans (FIRT LIFE-MAN),
and Appearance of humans and today (MAN-TODAY).
Axes have been normalized such that spacing
between Earth’s formation and today corresponds to
100%. Symbols as in Figure 3; recall that open
symbols are those students who believe the Earth is
500,000 years old or less. In contrast with Figure 5,
the thick, dashed black line demarcates a
“conceptual zone” for those students with a young
Earth perspective and the dashed gray line includes
most of the students from C. Notice that all but one
student with a young Earth view falls within the
young Earth zone; see text for additional explanation.
and the appearance of dinosaurs show quantitatively
that very few students (n=4) believe dinosaurs
originated when life did; these students fall on the black
diagonal line in Figure 3. As would be expected, few
students (n=2) place dinosaurs before the first
appearance of life, indicating that students generally
understand the timeline task and are not randomly
placing events along the timeline. Those students who
hold a young Earth view of Earth's age (open symbols)
generally place both events in the first half of Earth's
history. Almost all students, regardless of idea of
geologic time held, plot far from the position of the
accepted scientific model (black square in Figure 3). Most
students place the appearance of first life early in Earth's
history, in alignment with the scientific idea, but do not
comprehend the significant amount of time that passed
before dinosaurs appear in the fossil record.
While the placement of the origin of life is not
predictive of the placement of dinosaurs on the timeline
task, other events do appear to be highly dependent
upon one another, particularly for certain groups of
students. The relationship between the disappearance of
dinosaurs and the appearance of humans indicates that a
predictive relationship (R2~0.6) exists between these two
events (Figure 4). As indicated by standard content
analysis of timelines and written or verbal responses
discussed above, very few students (n=6) believe that
dinosaurs and humans co-existed. It is possible that
students who graphically represented humans and
dinosaurs co-existing did not actually hold this belief,
but were rather unable to depict events on the timeline
correctly. As our research methodology does not allow
us to distinguish between the two possibilities, we
analyze the data assuming minimal graphing skills,
although future analysis of student graphing ability
might be warranted.
Students with a young Earth model (open symbols)
are not necessarily those students with a dinosaur-man
coexistence model, as only two of the six students that
fall below the black diagonal line in Figure 4 hold a
young Earth model. In general, placement of the
disappearance of dinosaurs early in geologic times
suggests that students believe humans also appeared
early in time, with a similar relationship for events
placed later in time. Students from C, enrolled in an
Honors College course, position these events in the latter
half of geologic time (except for one student with a
young Earth view) and in a way that suggests a highly
predictive relationship. A polynomial regression
(dashed line; y =-1.66x2+3.14x-0.50, R2=0.94) through the
C data indicates that for this population of students the
placement of a single event on the timescale can be used
as a predictor of the placement of a second event. Finally,
unlike Figure 3, fourteen students plot very close to the
accepted scientific position that indicates that both
events happened late in Earth's history (Figure 4).
DISCUSSION
The analysis of qualitative data through traditional
content analysis coupled with investigation of
conceptual zoning on x-y graphs provides valuable
insight into student ideas about geologic time. The
majority of students in this study recognize that the Earth
is quite old, with a small subset of students holding a
"young Earth" perspective. In addition, most students
are able to place four events, the origin of life, the
appearance of dinosaurs and humans, and the extinction
of dinosaurs, in their correct order. On the other hand,
very few students created timelines that were similar to
the scientifically accepted one, indicating that the
relative spacing of events by students is non-scientific. A
few students believe dinosaurs and humans coexisted,
although in our study this belief is not correlated to a
young Earth perspective as reported by Schoon (1992).
Some discrepancy between timeline representations of
geologic time and written or verbal descriptions was
observed. This was particularly evident for student
conceptions of when life first appeared on Earth, and is
most likely indicative of instability in student ideas. In
essence, students may have been taught that life did not
exist when the Earth first formed, but may want or need
to believe that life did exist. As one student put it, "life
must have existed, [otherwise] where did we come
from?"
Representation of timeline data on ternary diagrams
through normalization of the spacing between four
events provides significant insight into student ideas of
geologic time (Figure 5). The timeline distances between
three pairs of events, normalized to the sum of these
distances, generates a ternary diagram from which
conceptual zoning can be identified. For example, Figure
5 illustrates a ternary diagram generated by evaluating
the distances between Earth's formation and the
appearance of first life (EARTH FORMS-FIRST LIFE), the
appearances of first life and humans (FIRST LIFE-MAN),
and the appearance of humans and the present day
(MAN-TODAY). Few students plot near the accepted
scientific idea (black square), although some sub-groups
Libarkin et al. - College Student Conceptions of Geological Time
419
GCI Question from Fall 2002 pre-instruction pilot
If you could travel back to the time when the Earth first formed as a planet, what type(s) of
life do you think you might encounter?
(A) There would be no life on Earth
(B) Simple, one-celled organisms only
(C) Plants only
(D) Animal and plant life in water, but none on land
(E) All types of life in water and on land, except people
(F) All types of life in water and on land, including people
Which of the figures above do you think most closely represents changes in life on Earth
over time? *
Response A
Response B
Response C
Response D
Response E
Number (n) of
respondents and %
students responding
n = 2481
32%
47%
3%
3%
8%
6%
n = 1089
10%
9%
37%
36%
8%
*Refer to Libarkin and Anderson (in press) for more details.
Table 3. Geoscience Concept Inventory (GCI) questions used for comparision with this study. Correct
responses are in italics.
of students do plot in distinct conceptual zones. In
particular, the majority of students enrolled in the
Honors College course at C plot close to the FIRST LIFE
MAN to EARTH FORMS-FIRST LIFE axis. This indicates
that these students recognize that humans appeared very
late in Earth's history. Interestingly, C students are
spread out along this axis, suggesting a range of ideas
about when life appeared on Earth. Those C students
who plot close to the EARTH FORMS-FIRST LIFE corner
believe that life did not exist on Earth for most of Earth's
history.
A second conceptual zone, labeled "young Earth
zone" on the diagram, encompasses eight of the nine
students who have either indicated that the earth is
<500,000 years, or provided information that suggests a
young Earth view (Figure 5). The single young Earth
student who plots outside of this zone described the
formation of the Earth as occurring "when man first
migrated to the American continents". It is unclear what
the student meant by this, and this was clearly a different
model than that held by other students with a young
Earth perspective. Two students who believed the Earth
was less than 500,000 years old explicitly demonstrated
creationist perspectives coinciding with their young
Earth view. These students wrote "Earth formed 6000
years ago. All life appeared shortly after during
420
'Creation'", and "7 days of creation" on their timelines.
Other students, also classified in the young Earth view,
indicated that the Earth formed during "creation", but
were unsure of the exact age of creation. The presence of
conceptual zones for both C students and students from
all schools with a "young Earth" perspective raises an
interesting question about where we would expect
students with scientific models of geologic time to plot
on ternary diagrams.
Comparison with GCI Data - Libarkin and Anderson
(2005) provide information about the entrenchment of
some geologic ideas despite instruction. As a population,
students nationwide seem to be familiar with the age of
the Earth, but are unclear about techniques used to
determine absolute age. In general, students tend to call
upon relative dating techniques, rather than
radioactivity, to explain how we know the Earth's age. In
addition, those students who do call upon radioactive
age-dating tend to focus on carbon-14 rather than
isotopes with longer half-lives.
GCI data related to the origin of life relative to
Earth's formation show a link between our timeline data
and the student population nationwide (Table 3). In an
earlier study, Libarkin and Anderson (2005) report that
47% of pre-instruction students (n=2481) believe that
Journal of Geoscience Education, v. 55, n. 5, November, 2007, p. 413-422
simple, one-celled organisms existed when the Earth first
formed, and this idea did not change significantly after
instruction. Only 32% of students completing the GCI
(Table 3) recognize that life did not exist when the Earth
first formed, in alignment with the 31% of students from
B and D described in the present study. The GCI data are,
however, in significant contrast to data from C and A
students; 88% of these students recognized that life did
not exist until at least 10% of geological time had passed.
The C students are clearly a population that holds a clear,
scientific conception of when life first originated in
Earth's history, and may simply reflect the educational
level and conceptual understanding required to place
them in an honors program.
In the nationwide GCI data, fourteen percent of
students believe that life on the early Earth was very
similar to today. This is in perfect agreement with the
nine students (14%) in our study who appeared to have a
young Earth perspective, some of whom described all
life being "created" at the same time. Finally, 37% of
students completing the GCI believe that dinosaurs came
into existence about halfway through geologic time
(Libarkin and Anderson, 2005; Table 3). This is similar to
the data reported here; 30% of the 61 students who
plotted the appearance of dinosaurs on their timeline
placed this event between 0.4 and 0.7 on the normalized
timeline.
CONCLUSIONS AND IMPLICATIONS FOR
RESEARCH AND TEACHING
The analysis of student conceptions of geologic time via
timeline analysis provides insight into college student
ideas of the Earth through time. Overall, the majority of
college students understand the relative order of major
biological
events
in
Earth's
history,
while
misunderstanding the time span between events. In
particular, students generally posit too much time
between the appearance and disappearance of terrestrial
dinosaurs, and too little time between the appearance of
the first life on Earth and the appearance of dinosaurs.
This suggests that the timescale of evolution is difficult
for students to comprehend, and needs to be addressed
explicitly in instruction. This includes discussion of both
the time required for the origin and evolution of simple
and complex organisms, as well as the scale of
organismal changes throughout Earth's history.
The importance of deep time in the development of
geological phenomena suggests that conceptions about
geologic time may directly impact ideas in other areas of
geology. The difficulties in understanding deep time
evident through analysis of interviews, time lines, and
ternary diagrams suggest that geoscience educators face
a
huge
challenge
in
improving
conceptual
understanding of the many concepts that use deep time
as a foundation, such as plate tectonics, erosion,
metamorphism, stratigraphy and sedimentation,
geologic structures, geologic resources, and global
change. For example, a sampling of ten introductory
geology textbooks found on one of the author's
bookshelves showed that all contained entire chapters
devoted to deep time, but only six of the ten covered time
in the introductory chapter. Of the six that did devote
part of the introductory chapter to deep time, detailed
chapters on deep time were placed, in general, mid-way
through the text. In fact, four of these six had Geologic
Time as Chapter 8, with total chapters ranging from
20-22 chapters. Another placed it as chapter 9 of a 20
chapter book, and the final one placed it dead last in a 20
chapter book. We suggest that a thorough discussion of
time as a basic concept in geology must occur in the
introductory stages of introductory courses. More
importantly, the effects of deep time on specific concepts
within geology must be reiterated throughout the course
to help students discover the influence of time on many
aspects of the geological sciences. Placement of topics in
textbooks clearly influences the timing of the discussion
of these topics in college courses, and we also suggest
that textbook authors reevaluate the positioning of
chapters on geologic time within textbooks.
Further investigation of the interaction between
conceptions of geologic time and other geologic
phenomena can provide additional insight into how
students develop ideas about the Earth. In addition, the
growing body of conceptions research in the Earth
Sciences points towards a need for change in how we
teach geology in K-12 classrooms. Consideration of the
role that deep time has to play in shaping our geologic
conceptions should be an important point to consider
when developing new curricula or pedagogies. Future
studies could investigate the relationship between ideas
about geologic time and how students build models of
Earth phenomena, compare the timescale of events in the
Earth's past, today, and in the future, and evaluate the
impact of time-related curricula on students'
Earth-related conceptual models.
The comparison between GCI data collected
nationwide and timeline data discussed in this study
indicates that some of the study findings are transferable
to the larger population of students while others are not.
Careful evaluation of data from future studies, including
comparison with results from existing studies, will be
required before conclusions about the larger population
can be made. Fortunately, the analytical approach, both
x-y and ternary plotting, used in comparing relative
positioning of events is applicable to any population as
this approach is independent of the specific ideas held by
students. The use of ternary diagrams in investigating
student conceptual understanding of geologic time has
potential as a predictive agent and method for classifying
students. This approach can be used for both research
and pre-instruction testing to aid faculty in designing
curricula that best fit students' pre-existing conceptions
of geologic time.
ACKNOWLEDGEMENTS
We thank all students who graciously participated in this
research as well as undergraduate students at Ohio
University who assisted in normalization of timelines.
This study was partially funded by the National Science
Foundation through an Assessment of Student
Achievement in Undergraduate Education grant to
Libarkin and Anderson (DUE-0127765). Any opinions,
findings, and conclusions or recommendations
expressed in this publication are those of the authors and
do not necessarily reflect the views of the National
Science Foundation.
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