Session 3 Powerpoint

"Doesn't the east coast of South America fit exactly against
the west coast of Africa, as if they had once been joined?”
"This is an idea I'll have to pursue.”
- letter to his future wife, December 1910
Alfred Lothar Wegener (1880-1930)
Alfred W.
Turns out, he wasn’t the first. Francis Bacon noticed this in
the 1600s.
In 1858, geographer Antonio Snider-Pellegrini made
these two maps showing his version of how the American
and African continents may once have fit together, then
later separated.
Evidence for continental drift:
1) The shapes of continents match
2) The rocks match
3) The plants match
4) The ice matches
Yet, the current positions don’t match
A ghoulish Alfred
A younger Alfred
A colder Alfred
Glacial evidence
This all lead to a theory…
The continents have moved
around the globe over time.
They were all together about 250
Million years ago (I’ll call it Pangea,
meaning “all the Earth” in Greek)
There was a southern megacontinent (Gondwana) and a
northern mega-continent
…and a whole lot of 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, University of Chicago
This sounds like
our kind of
I’ve seen better films
on laundry detergent.
A break in the action:
What makes a good scientific
Scientific Theory - A hypothesis or group of hypotheses
that: 1) Explains scientific observations; 2) Is tested
with repeated experiments and observations and found
always to work; and 3) Is accepted by the scientific
A good scientific theory:
1) Logical consistency
2) Agrees with the data.
3) Verifiable causes that explain and predict
4) Advanced comparisons (simplicity, tradeoff of
generality and specificity, distinction between non-fatal
difficulties and fatal difficulties)
Is continental drift a good
- Self consistent
- Agreed with available data
- Made specific, testable predictions
- Had difficulties, but weren’t fatal ones
Do you think people
know that we started
our careers as
German arctic
Ah, to be young
and freezing cold
again, Waldorf.
1) The older concept of land bridges to explain
fossil distributions became less likely.
2) The concept of a mobilistic Earth is brought
3) It allowed scientist to start making predictions
about fossil distributions, geological structures,
and earthquakes.
H. Cloos (famous geologist)
It placed an easily comprehensible, tremendously exciting
structure of ideas upon a solid foundation. It released the
continents from the Earth's core and transformed them into
icebergs of gneiss [granite] on a sea of basalt. It let them float
and drift, break apart and converge. Where they broke away,
cracks, rifts, trenches remain; where they collided, ranges of
folded mountains appear.
1950s: The bathymetry of the ocean floor.
Bruce Heezen
Marie Tharp
Harry Hess
Fred Vine and Drummand Matthews
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.
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