Geologic Explanation:
Thinking Like a Geologist
Philosophical Perspectives
from Robert Frodeman and
Carol E. Cleland
Classical Principles of Geologic Thinking
Uniformitarianism interprets the past with the
present in order to achieve the goal of
extrapolation.
Actualism constrains explanation with the laws of
chemistry and physics.
Temporal Reasoning follows “Steno’s Law of
Superposition ” and “Walther’s Law of Facies.”
Punctuated Equilibrium contrasts with Gradualism
as the mode and tempo of change.
Thinking Like a Geologist:
Sources
“Geological reasoning: Geology as an
interpretive and historical science”
Robert Frodeman, 1995
“Common cause explanation
and the search for a smoking gun”
Carol E. Cleland, 2013
An unrealistic understanding of
science presents dangers.
Belief in a universal methodology is
one such danger.
Understanding science in context
overcomes this danger; for example,
how [geologists] think.
Frodeman 1995
There is no science cookbook with
recipes for infallible answers.
Self-awareness of thinking helps scientists
do their work.
Geology models the nature of thinking within
the sciences and within everyday life better
than physics.
Frodeman 1995
Decisions require scientific and ethical
judgment (nuclear power, global warming).
Uncertainties and complexities abound.
Data are incomplete.
Reasonable assumptions fill the gaps.
Frodeman 1995
Two Schools of Philosophy
The Analytic
“Analytic” school emphasizes concern for
the natural world and builds upon logic and
facts presumed independent of theory.
In the analytic school, science consists of a
single set of logical procedures applicable
to all fields. All science reduces to physics,
and promises precise, reliable prediction.
Frodeman 1995
Two Schools of Philosophy
The Continental
“Continental” school emphasizes concern for cultural
and personal phenomena. It depends upon narrative
(story) to give meaning to the whole from its parts and
meaning to the parts from the whole.
Science may be a powerful tool, but it is not the only
way to know reality; “the” scientific method is a myth.
The theoretic assumptions that the scientist brings to
his or her work—what counts as significant, what work is
worth doing—structure to one degree or another all
that is examined, seen, and reported.
Frodeman 1995
Limits of the Analytic School:
Story subsumes logic.
Falsification (Popper) and Paradigm Shifts
(Kuhn) refute naïve inductivism.
Conceiving and acting shape thinking and
perception.
Discovery of “Deep” Time (Hutton’s “no
vestige of a beginning—no prospect of an
end”) has become a reliable truth.
Frodeman 1995
The Challenges to Geology
Incomplete data, poor resolution, lack of
experimental control, immense spans of
time, problematical direct observations:
Understanding cultural phenomena
(literature) faces similar challenges.
Frodeman 1995
The landscape is a text with chapters
written in stone.
Geologists “read” rocks and landscape. They
decipher the earth as text.
The unconformity , for example,
at Siccar Point
Frodeman 1995
Interpretive and Historical Practices
Historical entities are defined through time: the
Cascadia Subduction Zone, the Grand Canyon
of the Colorado River, and the Tibetan Plateau.
Identity and property are contingent upon history.
Historical entities, not “natural kinds,”
predominate and central subjects organize
geologic inquiry.
Frodeman 1995
The past is explainable; the future,
uncertain.
The goal in geology is not primarily to identify
general laws, but rather to chronicle the
particular events that occurred at a given
location (at the outcrop, in the region, or
across the entire planet).
This means that hypotheses are not testable
in the way they are in the experimental
sciences.
Frodeman, 1995
Interpretive inquiry recycles understanding
. . . as depicted on a concept map.
New thinking suggested by the parts revises
the conception of the whole.
New understanding of the whole improves
knowledge of the parts.
Tools lead to new conceptions; new
conceptions suggest new tools.
Frodeman 1995
“Common cause explanation and the search for
a smoking gun” Carol E. Cleland, 2013
OVERVIEW
 Myths about the scientific Method.
 Classical experimental science and prototypical
historical science: two different but equally rational and
objective patterns of evidential reasoning.
 How evidence acquired through field work justifies
historical hypotheses: Common cause explanation and
the search for a “smoking gun”.
Part I
Cleland, 2013
Myths about the Scientific method
 Inductivism: Scientists prove theories and
hypotheses by a logical process of
induction.
Cleland, 2013
Myths about the Scientific method
Falsificationism: Scientists falsify
theories and hypotheses by using
empirical evidence to refute them.
Cleland, 2013
The Logic of Prediction
Basic Concepts
1. Hypothesis (H):
(All C’s are E’s)
“Toy” Example
All copper expands when
heated.
2. Test Implication (I):
(If x is a C, then x is an
E.)
If sample of copper #4 is
heated, then it will expand
3. Test Condition (C):
(Heating copper sample #4)
4. Prediction (E):
(Copper sample #4 will
expand)
Cleland, 2013
The Logic of Evaluating the Results
of an Experiment
 Successful Prediction
1.
2.
C.
If H, then I
I
H
 Logical Fallacy: “affirming the consequent”.
(This is just another version of the problem of induction.)
Cleland, 2013
The Logic of Evaluating the Results
of an Experiment
 Failed Prediction
1.
2.
C.
If H, then I
Not-I
Not-H
 Valid Argument Form: “denying the consequent”.
(This explains the appeal of falsificationism.)
Cleland, 2013
The Terrible Truth about
Falsification
The form of the first premise in the
previous argument is:
If H and A, then I
(where ‘A’ stands for a set of auxiliary
assumptions {a1, a2, …, an} about other
conditions, known and unknown, about the
actual experimental situation.)
Cleland, 2013
The Terrible Truth about Falsificationism (continued)
 This changes the form of the
argument to:
1. If H and {a1, a2, …, an}, then I
2. Not-I
3. Not-(H and {a1, a2, …, an})
4. Not-H or not-{a1, a2, …, an}
5. Not-H or not-a1 or not-a2 or … or
not-an
(by De Morgan’s theorem)
Cleland, 2013
The Terrible Truth about Falsificationism (continued)
From a logical standpoint, no observation (whether
experimental or in the field), can conclusively
falsify a hypothesis. For it is always possible to
salvage the hypothesis in the face of a failed
prediction by denying an auxiliary assumption.
Cleland, 2013
Conclusion
Neither inductivism nor falsificationism
provides a satisfactory account of any
scientific practice; the scientific method of
yore is a myth.
Cleland, 2013
Part II
Differences in the methodology of classical
experimental science and prototypical historical,
natural science:
Is historical natural science methodologically
inferior to experimental science?
Cleland, 2013
The structure of
Classical Experimental Science
 Focus: Is on a single (sometimes complex) hypothesis
which typically has the form of a universal generalization
(All C’s are E’s).
 Central Research Activity: Consists in repeatedly
bringing about the test conditions specified by the
hypothesis and controlling for extraneous conditions
that might be responsible for false positives and false
negatives.
Cleland, 2013
The structure of
Prototypical Historical Science
Focus: Is on proliferating multiple, rival hypotheses
to explain a puzzling body of traces of past
events (data) encountered in field work.
Central Research Activity: Consists in searching
for a ‘smoking gun’ a trace(s) that sets apart
one or more hypotheses as providing a better
explanation for the body of traces thus far
acquired than the others.
Cleland, 2013
A Case Study
The Alvarez Hypothesis



Two-pronged hypothesis: 1) impact; 2) extinction.
Initially many different explanations for the endCretaceous mass extinction: pandemic, evolutionary
senescence, climate change, supernova, volcanism,
and meteorite Impact.
Discovery of an iridium anomaly (“smoking gun”) in
K-T boundary sediments narrowed it down to two
possibilities: volcanism and meteorite impact.
Discovery of extensive quantities of a rare form of
shocked mineral subsequently cinched the case for
impact over volcanism.
Cleland, 2013
A Case Study: The Alvarez Hypothesis (cont)
 Paleontologists weren’t convinced: They
agreed that there had been a meteorite impact
but many doubted that it caused the endCretaceous extinctions.
 The discovery of extensive pertinent fossil evidence
(especially small organisms such as foraminifera and
ammonites, and fern spores and angiosperm pollin) on
either side of the K-T boundary was pivotal in
changing their minds, providing the needed smoking
gun for the second prong (mass extinction) of the
hypothesis.
Cleland, 2013
The Evaluation of Historical Hypotheses
 Grounded in explanatory power:
 Hypotheses are accepted and rejected in virtue of
their power to explain (vs. predict) puzzling bodies of
traces discovered through field work.
 The Alvarez hypothesis explains an otherwise
puzzling association (correlation) among traces better
than any of its rivals. It is for this reason that it is
viewed as ‘confirmed’ and its rivals are no longer
seriously entertained by scientists.
Cleland, 2013
Part III
Common cause explanation
Cleland, 2013
Common Cause explanation

Reichenbach’s Principle of the Common Cause: seemingly
improbable associations (correlations or similarities) among
traces are best explained by reference to a common cause.
C

E1
E2
E3
E4
Presupposes that the temporal structure of causal
relations in our universe is such that most (not all) events
form causal forks opening from past to future (leave many
traces in the future).
Cleland, 2013
The Asymmetry of Overdetermination
 A time asymmetry of causation:
Most local events & structures overdetermine their
past causes (because the latter typically leave
extensive and diverse effects)and underdetermine
their future effects (because they rarely constitute
the total cause of an effect)
 Much easier to infer an ancient volcanic eruption than a near future
volcanic eruption.
Cleland, 2013
An illustration: The colors of
dinosaurs
Asym of OD Asserts that the present is filled with
overdetermining traces of the past; hence
one can never completely rule out finding a “smoking gun”
for any scientific hypothesis about the past. The
methodology of historical field work is based upon
this possibility.
Cleland, 2013
Conclusions
1. Historical Scientists exploit the
overdetermination of the past by the localized
present by searching for a common cause
(“smoking gun”) to discriminate among competing
hypotheses; the asymmetry of
overdetermination guarantees there are likely to
be many such telling traces. The problem is
recognizing them for what they represent.
Cleland, 2013
Conclusions
2. The methodology of historical science is
different from that of classical
experimental science but it is not inferior;
each practice is designed to exploit the
differing information that nature puts at
its disposal.
Cleland, 2013
Cleland References
 “Common cause explanation and the search for a smoking gun” in Baker, V.
(ed.), 125th Anniversary volume of the Geological Society of America
(forthcoming).
 “Prediction and Explanation in Historical Natural Science,” British Journal of
Philosophy of Science 62 (2011), 551-582.
 “Philosophical issues in natural history and its historiography” in Tucker,
A. (ed.), Blackwell Companions to Philosophy: A Companion to the
Philosophy of History and Historiography. Oxford: Blackwell Pub.
(2009), pp. 44-62.
 “Methodological and Epistemic Differences Between Historical Science and
Experimental Science,” Philosophy of Science 69, (2002), pp. 474-496.
 “Historical science, experimental science, and the scientific method,” Geology
29, (2001), pp. 987-990.