Transcript Plate Tectonics 2

Science is a process of separating the
demonstrably false, from the probably true.
- Michael Zimmerman
Image from Minnesota Citizens for
Science Education.
This is a case of
extraordinary science!
"If we are to believe [this] hypothesis, we must
forget everything we have learned in the last 70
years and start all over again” –R. Chamberlin
(American geologist)
Image from Wikipedia used under educational use rationale.
During the plate tectonics revolution, geologists
get rid of most of their large-scale
INTERPRETATIONS (NOT observations) of the
planet works. This occurs with paradigm shifts.
Evidence for the theory of continental drift:
1) The shapes of continents match
2) The geological maps match (stratigraphy &
others)
3) The fossil match (paleontological)
4) The rocks record features that indicate that
ice was present in the past (paleoclimatic)
This evidence is all geologic and mostly
qualitative.
Evidence for the theory of plate tectonics:
1) Deep earthquake epicenters located along dipping
plane (1930s).
2) Paleomagnetic evidence indicating that the N pole
drifted over time (1950s).
3) Maps of seafloor indicating a mountain range in
middle of the Atlantic (1950s)
4) Magnetic reversals on seafloor, suggesting seafloor
is spreading and youngest in the middle (1940s,
1950s).
5) Models of the Earth consisting of 12 rigid tectonic
plates (1960s).
This evidence is all geophysical and quantitative.
1930s
Image from biography on the
Pennsylvania State University website.
Kiyoo Wadati of Japan
1950s
Earth’s magnetic field
Image source.
Image credit: Paleomagnetism Chapter 10 by Robert Butler, University of Arizona.
Image from Wikipedia used under educational reuse rationale.
Marie Tharp
Bruce Heezen
Harry Hess
Image courtesy of PBS.org.
Aye, aye, Captain
Diagrams depicting mid-ocean ridges and
normal vs. reversed magnetic polarity. Can be
obtained from Don Reed’s website (San Jose
State University) .
Image source: Müller, R.D., M. Sdrolias, C. Gaina, and W.R. Roest 2008. Age, spreading rates and spreading symmetry of the
world's ocean crust, Geochem. Geophys. Geosyst., 9, Q04006,doi:10.1029/2007GC001743.
Image obtained from NOAA.
In 1967, W. Jason Morgan proposed that the
Earth's surface consists of 12 rigid plates
that move relative to each other.
Two months later, in 1968, Xavier Le Pichon
published a complete model based on 6
major plates with their relative motions.
Le Pichon
Morgan
Image courtesy of Princeton Weekly Bulletin.
Image from Le Pichon’s Facebook site.
Image courtesy of USGS.
Geologists have been working for now 40 years trying to test and
refine the theory of plate tectonics. This is a return to “normal
science” in Kuhn’s sense.
Is plate tectonics a good scientific
theory?
It is a theory because it: 1) Explains scientific
observations; 2) Is tested with repeated
observations and found always to work; and 3) Is
accepted by the scientific community.
A good scientific theory:
1) YES! Logical consistency - parts of it don’t contradict
other parts
2) YES! Agrees with the data.
3) YES! Suggests verifiable causes that explain and
predict
BUT, note that it doesn’t explain how plates moves.
What happens to continental drift?
The theory of continental drift is added as a part
of the theory of plate tectonics. This
“engulfing” of one theory by another theory is
relatively common.
And now to boldly go where science
classes don’t – the nature of science
Image removed due to copyright: USS Enterprise.
Why did North American Scientists
reject the Theory of Continental Drift
1) Methodological differences of the geologists
(uniformitarianism & multiple working
hypotheses)
2) Role of Isostacy
3) Emphasis on physics-based approaches
(instrumentation and theoretical approaches)
I’ll provide some nature of
science commentary
Image courtesy of Ragesoss.
Back to G.K. Gilbert.
He came up with a
very good way of
collecting empirical
field data: Multiple
working hypotheses.
It is still used by field
geologists, because it
works very well.
Image courtesy of USGS.
G. K. Gilbert
Multiple working hypotheses
Geologists are faced with a baffling array of
features in any area, of which they have to
make sense. The so-called scientific method
(observation->prediction->hypotheses>experiment) doesn’t work very well.
Gilbert notices that rather than only forming
one hypothesis, it is better to have several in
mind and see which one fits the facts better.
Image from Wikimedia Commons.
The idea of
multiple working
hypotheses is
picked up by T.C.
Chamberlin, a
major intellectual
force at the time.
Chamberlin was at the University of
Wisconsin, for a good portion of his
academic career. He was also president
or the University (He eventually moved
to the University of Chicago).
I am confident, therefore, that general
application of this method to the affairs of
social and civic life would go far to remove
those misunderstandings, misjudgments, and
misrepresentations which constitute so
pervasive an evil in our social and our political
atmospheres, the source of immeasurable
suffering to the best and most sensitive souls.
Image source: Wikimedia Commons.
Hmmm, sounds almost
like a political statement.
Naomi Oreskes
Image source: Oreskes’ faculty page, UCSD.
Oreskes maintains that the concept of “multiple
working hypotheses” is a particularly American
invention. It embodies the broadest and deepest
convictions of Americans: It was the idea that all
ideas have their place and should be treated equally
and fairly. Further, it was a reaction to the way
geological science was being conducted in Europe,
mostly following the theoretical musings of
prominent scientists that were not based on
observations.
Multiple working hypotheses therefore becomes
THE methodological way that geological science gets
done.
I am confident, therefore, that general
application of this method to the affairs of
social and civic life would go far to remove
those misunderstandings, misjudgments, and
misrepresentations which constitute so
pervasive an evil in our social and our political
atmospheres, the source of immeasurable
suffering to the best and most sensitive souls.
Image source: Wikimedia Commons.
It IS a political statement.
Naomi Oreskes
Image source: Oreskes’ faculty page, UCSD.
Plus, it outlived its place in
geology as fieldwork lost the
center stage.
Which leads us back to Wegener and his
theory of continental drift….
Image from Wikimedia Commons.
…and the American criticism.
"Utter, damned rot!” -W.B. Scott
"If we are to believe [this] hypothesis, we must forget everything we have
learned in the last 70 years and start all over again” -American scientist
"Wegener's hypothesis in general is of the footloose type, in that it takes
considerable liberty with our globe, and is less bound by restrictions or tied
down by awkward, ugly facts than most of its rival theories."
- Dr. Rollin T. Chamberlin (TC Chamberlin’s son)
By declining to consider
alternative frameworks,
Wegener violated the
American ideal of applying
democratic principles to
the development of
scientific theory.
Image courtesy of Ragesoss.
Hmmm, I wonder what else I
did wrong?
Image source: USGS.
Alfred W.
For the record, the “official” scientific line for rejection of
continental drift was the lack of a mechanism.
Wegener assumed that
the continents moved through the rocks at
th at made up the
oceanic crust. Thus
, the ma jor probl e m was
findi n g forces that could make the co
n tin ents "plow around
in the
mantle " (in the words of a
critic ). Wegener tentatively suggested
both centrifugal force ca
u s ed by the rotation of the Ea
rth (whi ch
would move continents to the equator
) and tidal - type waves in t
he
Earth itself generated by the gravitati
o nal pu ll of the sun a nd moon.
Wegener suspected these forces were inadequate
to mo ve
contients . "It is probable the complete
solution of the problem of
the forces will be a long time coming," he predicted in his l
ast
(1929 ) revision. "The Newton of drift
t heory has not yet appea red."
If he does appear, after
being dead for 2 centuries,
Did you hear what
I say let’s throw an apple
the man said and make a run for it.
Image removed
The Newton hasn’t
due to copyright:
appeared.
Statler and
Waldorf Jim
Henson puppets.
This makes no sense. Plate
tectonics, when accepted,
also lacks a mechanism.
That is, why do not know
why the plates move.
Image courtesy of Ragesoss.
Hmmm, this isn’t what I was taught, but it is correct. The
development of scientific knowledge is inescapably
historical, because scientists make choices based on biases
(methodological, disciplinary, and evidential).
While it was easier to be a field geologist without this
information, I am a better field geologist with more
scientific integrity knowing it.
There were other social problems:
1) Wegener was not a geologist, and therefore lacked
credibility;
2) The evidence was from the southern hemisphere, so
most geologists from Europe and US had not seen
the data; and
3) The geophysical community, particularly in North
America, did not accept the idea (for reasons that
are about to be explained).
How did we get into
a continental drift
lecture?
Image removed
due to copyright:
Statler and
Waldorf Jim
Henson puppets.
I think because
everything’s
gone (drifted)
South.
The US geophysical community was a
bit of an obstacle.
Come to the dark side. Accept
theoretical constructs and the precise
instrumental measurements only.
Image removed
due to copyright:
Darth Vader.
Image from Wikimedia Commons.
Image from NOAA, found on Wikipedia.
Ok, really, they didn’t look that mean, but they
did basically stop continental drift from
happening – by studying a principle called
isostacy.
Hayford
Bowie
A brief summary of isostacy
Amazing!
Image from Wikimedia Commons.
During the survey of India
by the British in the 1800s
(headed up by Sir G.
Everest), they noticed an
amazing thing: A plumb bob
is deflected from vertical by
the Himalayan mountains.
Hmmmm.
Image from Wikimedia Commons.
It turns out, one would expect that result because the
mountains are exerting a gravitational force. The
problem was that the deflection was LESS than it should
have been. Two possibilities were proposed:
1. The mountains have roots that sit in the Earth’s
mantle (the next layer down), very much like an
iceberg. This is called Airy isostacy; or
2. The crust has a constant thickness, but the density of
rocks below the mountains is less than that below
the plains. This is called Pratt isostacy.
Airy isostacy
Pratt isostacy
U.S. Coast & Geodetic Survey
It turns out, when you try to make an accurate
map, you need to know a precise shape for
the shape of the Earth. It turns out that G.K.
Gilbert (remember him?) figured out a way of
doing that by measuring gravity very precisely
everywhere.
Image from Wikimedia Commons.
Hayford, however, carries it one step farther and makes
even better calculations. He found the same results as
before, that the deflections were too small (as did Pratt
before him). Therefore, he assumes Pratt’s model is
correct.
“There must be some general law of
distribution of subsurface densities which
fixes a relation between subsurface
densities and the surface elevations…”
So, scientists generally accept this METHOD because it
is quite effective at making maps. They also assume
that the MODEL is correct (which is incorrect).
So, Isostacy becomes fact.
“Isostasy must, today, be regarded as fact which
has been tested by many
observation…Hayford’s work in America (later
Hayford’s and Bowie’s) may be regarded as
having decisively elevated theory into fact.”
-Sir Harold Jeffreys
Theories are not uniquely
confirmed by their
predictions…Theories can
be right in some respects
and wrong in others. The
Pratt model of isostacy
was correct with respect to
the existence of isostatic
compensation, but not
with respect to how that
compensation was
achieved.
Image courtesy of Ragesoss.
Image from Wikimedia Commons.
Hayford, Bowie, and Jeffreys form a powerful alliance
against continental drift. In fact, they do not even
consider that geological evidence is worth considering.
I don’t even consider
continental drift as an option,
because is violates the “truth”
of Pratt isostacy.
So, things are not looking so good for Wegener.
Nicht so gut.
Image source: USGS.
Image removed due to copyright – Gary Larsen’s The Far Side
Continental Drift -- Whiplash
The geophysicists would
not accept any inductive,
geological evidence. They
would only trust their
theoretically driven,
quantitative data.
Image courtesy of Ragesoss.
Oreskes proposes as evidence
of this statement the “Bullard
fit” (how the continents fit
back together). This
reconstruction was proposed
by geophysicist Bullard at
Cambridge University, and
used as evidence by the
geophysical community for
plate tectonics (it appeared in
most textbooks for the next
30 years).
Oreskes maintains that this map was NOTHING
that Wegener had not proposed before.
From Walter Munk (distinguished
geophysicist)
"In this controversy between physicists and
geologists, the physicists, it would seem, have
come out second best! They gave decisive
reasons why polar wandering (read: continental
drift) could not be true when it was weakly
supported by paleoclimatic evidence, and now
that rather convincing paleomagnetic (i.e.
physical) evidence has been discovered, they find
equally decisive reasons why it could not have
been otherwise."
Nature of science
Oreskes starts her chapter with this quote by J.S.
Mill: “While everyone well knows himself to
be fallible, very few think it necessary to take
precautions against their own fallibility.”
How does this quote relate to her chapter and
Feynman’s idea of scientific integrity?
"The young specialist in English Lit ... lectured me
severely on the fact that in every century people
have thought they understood the Universe at
last, and in every century they were proved to be
wrong. It follows that the one thing we can say
about our modern 'knowledge' is that it is wrong.
... My answer to him was, '... When people
thought the Earth was flat, they were wrong.
When people thought the Earth was spherical
they were wrong. But if you think that thinking
the Earth is spherical is just as wrong as thinking
the Earth is flat, then your view is wronger than
both of them put together.”
- Isaac Asimov
Did Wegener know this theory was
going to be a bit, well, controversial?
"if it turns out that sense and meaning are now becoming evident
in the whole history of the Earth's development, why should we
hesitate to toss the old views overboard?”
- letter to future father-in-law, well-known climatologist Wladimir
Koppen
Image source: Wikipedia, US public domain.
Sounds like a
scientist.
Image removed
due to copyright:
Statler and
Waldorf Jim
Henson puppets.
Sounds like he’s never
getting married.