Catastrophism,
Uniformitarianism, and
Gradualism
Or, how humans have thought
about geologic processes
Neptunism
• Abraham Gottlob Werner, 1787
• All rocks precipitated from ocean water
• Problems?
Catastrophism
• Baron Georges Cuvier, late
18th – mid-19th century
• Researched fossils and
extinction
• Series of six major
catastrophes
•
•
“All of these facts, consistent
among themselves, and not
opposed by any report, seem to
me to prove the existence of a
world previous to ours,
destroyed by some kind of
catastrophe.”
Problems?
James Hutton and Uniformitarianism
• “The past history of our
globe must be explained by
what can be seen to be
happening now.”
• Plutonism - igneous rocks
result from the cooling of hot
magma
• What kinds of processes did
Hutton imagine had shaped
the world in the past?
Siccar Point
Hutton’s Unconformity
Photo credit: Dave Souza, Wikimedia Commons
Evidence of mountain-building
Charles Lyell
• Principles of Geology
• “The present is the key to the
past.”
• Much better writer than
Hutton; disseminated idea of
Uniformitarianism to a much
wider audience
Lyell and Darwin
Charles Darwin
• Lyell was one of the first
scientists to endorse On
the Origin of Species,
although he disagreed
with aspects of the
theory of natural
selection
• Why would Lyell’s work
have been useful to
Darwin?
Why is Uniformitarianism a more logical
approach to understanding Earth history?
• Constancy of laws: In order to meaningfully study the past, we
must assume the same or similar mechanisms operated then as
now. Otherwise, how can we know anything about the past?
• Parsimony: “Occam’s razor”
• We know the earth is extremely old (how?)
Does Uniformitarianism mean that nature
is ALWAYS constant?
• “Geologists do not deny uniformitarianism in its true
sense, that is to say, of interpreting the past by
means of the processes that are seen going on at the
present day, so long as we remember that the
periodic catastrophe is one of those processes.
Those periodic catastrophes make more showing in
the stratigraphical record than we have hitherto
assumed.”
–
Ager, Derek V. (1993). The Nature of the Stratigraphical Record, 3rd Ed.. Chichester,
New York, Brisbane, Toronto, Singapore: John Wiley & Sons. pp. 83–84.
From Uniformitarianism/Gradualism
to “Actualism”
• Uniformitarianism
was a huge step in
the right direction
• Evidence exists that
there have been
different intensities
of geological activity
during the past
Deccan Traps near Mumbai, India
Series of intense volcanic eruptions ~66 mya