🚀 go-pugleaf

In article <531@weitek.UUCP> mae@weitek.UUCP (Mike Ekberg) writes:
>About ten years ago, while I was in college, I read a book that presented
>a theory to explain many of the phenomenon used to back up the theory of
>plate tectonics.
>
>The theory went something like this...
>
>The earth consists of a large gob of semi-liquid stuff(mantle) that is coated
>with an extremly thin shell of hardened goop, ie crust. Occasionally,
>for unknown reasons, the thin shell 'slips' over the surface of the
>semi-liquid stuff. After a while, the shell movement reaches some sort
>of equilibrium(sort of like Punctuated Revolution? :-} ).
>
>This theory 'explains' the following phenomenon:
>
>1. magnetic reversals          - since the magnetic pole is in the mantle,
>                                 when the crust shifts relative to the
>                                 mantle, the apparent direction of the
>                                 earths magnetic field shifts.

It doesn't explain why the field shifts direction 180 degrees. Not unless
you really believe that the entire crust rotates exactly 180 degrees
around some equatorial pole. I find that incredibly hard to believe.

>2. sea floor expansion         - since the earth is not a perfect sphere,
>                                 when the crust shifts, cracks open as the
>                                 crust gets stretched of the bulgy parts.
>                                 Stuff leakes out from the interior.

All right, I guess you need some explaination of plate tectonics (and the
evidence for it.) Okay, Seafloor spreading:  Around the world there are
ridges in the ocean, called mid-ocean ridges. There is a lot of volcanism
there. On both sides of these ridges you can find magnetic reversal
patterns (symmetric) which correspond to the dated patterns of magnetic
reversal on the continents. Now, these patterns had to be imprinted in
the rock when it was very hot, above a temperature called the curie
temperature (can't remember off hand how hot that is, but it's a lot
hotter than is normally found.) Basically it was laid in when the rock
solidified. These are fairly continuous patterns dating back over 170
million years, with reversals every million years or so (sometimes
much more often). The spreading is at a relatively continuous rate,
at least at this time scale. Any theory must account for this.
Somehow I find it much easier to believe slow continuous spreading
than occaisional massive shifts of the entire crust, which simulate
slow spreading sooo well.

>3. weird fossil records                - the author sited examples of fossils of
>                                 tropical plants in Siberia. Siberia used
>                                 to be on the equator.

According to plate tectonics, the continents are drifting. They move
slowly, but they do move. Siberia was tropical once, according to plate
tectonics.

>Is there anything to this theory or is it totally from left field?

I haven't even mentioned that seismic evidence supports this stuff,
and that spreading is occuring today (measurably). To say nothing
of subduction zones (ocean trenches, where ocean crust goes back
down into the mantle to be recycled).

>BTW, according to the Grab Bag column in the S. F. Examiner, the crust is
>much thinner relative to the inside then an egg shell is to the egg.

Well, I don't know how thin an eggshell is, but that's definitely
true.  The oceanic crust is about 7km thick, and the continental
crust is about 35km thick. The Earth is 6370km in radius, so using
continental crust, the crust is 0.55% of the Earth's radius.
If an egg is 3cm in radius (a pretty large egg), the equivalent thickness
of the crust is 0.16mm. That's a pretty thin shell.


			Bob Myers