1. Uniformitarianism, or Actualism.
2. Multiple Working Hypotheses.
3. Principle of Parsimony
4. Inductive - Deductive Reasoning
5. Scientific Proof vs. Absolute
Proof
 6. Retrodiction – prediction in a
backward direction.
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 Uniformitarianism
was
developed by James Hutton in
the 1790’s.
 Charles Lyell in the 1830’s
popularized Hutton’s writings.
James Hutton: first modern geologist (1790s)
whose ideas were the basis for uniformitarianism
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Charles Lyell, a
founder of
modern geology.
He popularized
Hutton’s ideas by
coining the term
uniformitarianism
in the 1830s.
Charles Lyell, 1797-1875
Lyell’s Grave in Westminster Abbey, London
 Uniformitarianism
rejected
supernatural explanations
and held that present
processes operated
uniformly in the past.
 “The present is the key to
the past.”
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Many geologists use the
German term actualism.
 Actualism - Physical and
chemical laws are constant over
geologic time.

Mudcracks in a dried up pond
Ancient mudcracks in
sedimentary rocks.
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Ripples formed by water flow on a
modern beach.
Ripples formed by water flow in an
estuary.
Ripples formed by wind on a
sand dune.
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Ripples in a sandstone, millions of years
old, formed by water or wind.
Ancient ripples
preserved in
sandstone 300 MY
old in Colorado.
The beds were
originally horizontal
but have been tilted
by mountain
building processes.
 Scientists
seek as many
explanations or hypotheses
as possible for a given
phenomenon.
 Each hypothesis is then
tested.
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 If
only one hypothesis is
constructed, data may be
collected to support only this
hypothesis.
 Conflicting data may be
ignored.
 The hypothesis will be bent to
fit the new data.
 Absence
of an alternative
explanation is no assurance
that the truth has been
discovered.
 An example: Your car is
missing from where you
parked it.
 What happened to the
 It was towed.
 It rolled away down a
car?
hill.
 It was stolen.
 Your friend with a key
borrowed it.
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 Extinction of the Dinosaurs
 Asteroid impact?
 Climate change?
 Disease?
 Volcanic eruptions?
 Competition with mammals?
The best hypothesis is usually
the simplest hypothesis
(requires the fewest
assumptions).
 Complex hypotheses are less
likely to be true.
 Beware of clever hypotheses.
e.g., who designed the
Egyptian pyramids?

 Induction
- developing
conclusions from facts.
Thought by some to be the
essence of objectivity.
 Deduction - predicting results
from a known principle.
 Induction-deduction work
together.
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Example:
 Sand bars form in flowing water
(rivers, streams, or ocean currents).


Induction
These bars are cross bedded.
Induction
Thus, similar sized cross-bedded
sandstones in a rock outcrop formed
in flowing water. Deduction
Sand bars in a river
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Cross Beds
FLOW
FLOW
Cross Beds that formed
in flowing water
FLOW
Wind-blown
cross beds are
typically larger
in scale than
water-laid cross
beds.
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Scientific proof - a matter of
probability.
 Absolute proof - a matter of
certainty. e.g. a2+b2=c2 for a
right triangle; or sodium and
chlorine always form salt (NaCl);
or the Second Law of
Thermodynamics always applies.
 Few things are absolutely certain.
 Science deals with probabilities.

 Scientists
cannot
prove a hypothesis
or theory to be true.
 Scientists can falsify
hypotheses.
 Hypotheses that
Hypothesis:
cannot be falsified Dinosaurs went
are the best
extinct at the end of
explanations
the Cretaceous.
available.
How would you
falsify this?
Example:
 The blood type from the criminal
at the crime scene does not
match the defendant’s. What
does that indicate?
 The blood type from the criminal
at the crime scene does
match the defendant’s.
What does that indicate?
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 Good
science requires
accurate collection of data
and an honest attempt to
falsify available hypotheses.
 False hypotheses do little
harm.
 False “facts” do great harm.
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Experimental Scientists use
prediction to test their
hypotheses.
Historical Scientists use
retrodiction to explain a past
event.
Example: plants grown in high
CO2 concentrations have fewer
stomata. Stomata density on
fossil plants is used to
estimate past CO2 levels in the
atmosphere.
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