Re: Pangaea

[art@acc.com (Art Berggreen)]

>
>I don't know if this is the best forum for this, but I do know that
>these are the best people to ask.

Well, I'll give you my amateur viewpoint.

>I have always had a problem with the concept of Pangaea. (is that
>spelled right?)  I didn't want to through this out without some
>careful forethought, so here it is after several days of revising.

With an open mind, questioning is a very good habit.

>1) The concept of making "puzzle pieces" out of today's continents
>and fitting them into a picture of the original continent seems,
>well, childish.  Considering what I have heard about all of the 
>other significant changes in the earth over the millions of years
>that scientists have, as yet, figured out, it seems inconceivable
>for the above-sea-level land masses to remain largely unchanged.
>( This is the most insupportable of my objections to the theory of
>Pangaea.  I do understand that supporting the theory is a lot of
>research showing similarities between coastal areas of different
>continents. )

I think that this is kind of response Wegner got when he first
proposed the idea.  Of course he also had a number of other
data items, like similar geologic structures and fossils of
similar ages where things fit back together.  The big problem
at that time was believing that the continents could move.
It wasn't until paleomagnetism studies indicated that sea floor
spreading was happening that the theory started to be accepted.
I believe that the continents "fit" better if you locate
continental margins independent of sea levels (using the edge
of the continental shelf).

It's often hard to get a mental grasp of the size and time
scales in geology.  On a scale the size of the Earth, the things
we humans consider large, just aren't.  The Earth is actually
fairly smooth, with thin veneers of differentiated crust, water
and atmosphere.  Our biggest mountains are really pretty small
wrinkles at this scale.  These wrinkles may change, but the
structures they are on, have much longer lifespans.

>2) The "continental drift" as it applies to the theory of Pangaea.
>I am not a geologist or whatever "-ist" deals with the movement of
>the earth's plates.  I only understand that there is a certain
>amount of "drift" of the plates that moves them potentially apart
>from each other.  ( I can't remember if this is why California is
>sliding into the ocean or not.  Maybe just a modern myth. )  Is
>it really feasible for the plates containing the major land 
>masses to move as dramatically as they have?  How big are the
>plates?  How many plates made up Pangaea?

California is not sliding into the ocean.  But part of California
is continental crust sitting on the Pacific plate.  Since the Pacific
plate is moving north-west relative to the North American plate, this
sliver of California is moving north-west relative to rest of
California along the plate boundary known as the San Andreas fault
system.  If I remember correctly, most relative plate motion is on
the order of a few centimeters per year.  Over millions of years,
it adds up.  It often moves in small jumps.  The 1906 San Francisco
quake showed fault movement on the order of 20 feet. Most of the
continental land masses are composed of a very small number of plates.

>3) What is the theory for the creation of Pangaea?  What would
>cause a planet to form with all its higher land mass to form on
>one side?  Was it on the side or was it formed at one of the poles?
>Is a planet stable with this deformity?  Is that the reasoning
>for the breakup of Pangaea?  These are questions I have never 
>seen discussed when I have read about Pangaea.  

I don't think that the position of the continents have much effect
on the angular momentum of the Earth (climate may be a different
story!).  Also, the continents are actually the lighter parts of
the crust.  If I remember right, computer simulations of plate
models show this clustering and breaking up.  One theory for the
breakup of pangaea, is changes in the convection cells in the
mantle which caused new plate boundaries and spreading centers
to form.

>4) About the breakup, this has been blamed/credited for dividing
>the dinosaur families according to the area of Pangaea.  Is this
>an over-generalization?  Now that dinosaurs are being found in
>areas thought to be out of reach due to the breakup, suddenly
>we have a "land-bridge".  Forgive me for being sacrilegious, but
>this *sounds* like someone's pet theory was being disproved and
>everyone rushed to save it.  It seems that only the surface of
>dinosaur fossils has been touched.  What will happen if more
>out-of-bounds dinosaurs are found?  Will Pangaea start to look
>like a quilt with "land-bridges" and other patches criss-
>crossing the dinosaur map?  ( This is the list's area of 
>expertise.  Feel free to be offended and refute my assertions. )

The dinosaur fossil record is far from complete or well understood.
The details of the past continental arrangements are also hard to
find.  Sure, new information always raises questions, but there
is an awful lot of evidence for plate tectonics that can't be
dismissed easily.

>5) On more earth-formation issue: I recall reading that the 
>surface of the earth is constantly rising and falling.  Land
>masses pop up in the middle of the ocean causing islands to
>form.  I also remember reading of how the highest mountains
>were once thriving forests and plains.  ( This was in a story
>about amber and why it is found in the mountains. )  It seems
>that if the earth's surface is going up and down on a steady
>basis ( we won't talk about Atlantis  8-D ) then what are the
>continents now weren't necessarily continents then.  Was 
>Pangaea pieced together using the plates or the above-sea-level
>continents?  Using the plates would easily defeat this question.
>Using the continents would not.

First of all, remember the scale of this activity is quite small
compared to the Earth.  Also, most of this activity is better
explained by plate tectonics that any alternatives.  There is
evidence that large continental plates don't change that much
over geologic time.  Some pieces of continental crust sometimes
get split off one continent and rafted on an oceanic plate only
to get stuck onto another continent.  And continental plates
occasionaly break (like the East Africa rift today).

>OK, I'm done using up your bandwidth.  I just had to get this
>out in order to fully understand some of the discussions going
>on here.

No, these questions are quite valid.

>Joe Average     :->     71573.2027@compuserve.com

Art