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From: bob@uhmanoa.UUCP (Bob Cunningham)
Newsgroups: sci.misc
Subject: Re: alternative to plate tectonics
Message-ID: <146@uhmanoa.UUCP>
Date: Thu, 4-Dec-86 12:47:50 EST
Article-I.D.: uhmanoa.146
Posted: Thu Dec  4 12:47:50 1986
Date-Received: Fri, 5-Dec-86 21:07:13 EST
References: <531@weitek.UUCP> <1272@cit-vax.Caltech.Edu> <1273@cit-vax.Caltech.Edu>
Organization: Hawaii Institute of Geophysics
Lines: 40

> A slightly better alternative than the previous one is the
> Expanding Earth hypothesis. This explains seafloor spreading by
> expansion of the Earth's interior, causing the crust to stretch.

Unfortunately, the Expanding Earth hypothesis ignores several decades of
research involving hot spots, subduction zones, active margins, 
island arcs, and passive margins.

The critical evidence which lead to the clear identification of the deep
oceanic trenches (or, more precisely the "Benioff zones" associated with
them) with sinking tongues of oceanic lithosphere came from work done on
the Tonga Trench in the mid 1960s using the World-Wide Standardized
Seismograph Network.  Subduction was clearly shown.  Since then, the same
essential picture has been seen at the other major trenches.

Also, very careful measurements of plate movements have been made, using
not only paleological and magnetic analyses, but also using careful
surveying techniques, including measurements using satellite navigation
techniques.  Turns out that the plates are definitely moving around at
relatively rapid speeds (well, rapidly geologically speaking) of the order
of centimeters per year.  One of the problems has been trying to determine
what to use as a global reference that could be considered relatively
static (sort of a geological version of "relativity" :-).  The current
popular static reference is the means of the global "hot spots" which don't
seem to move too much relative to each other.

To see the effects of a plate (the Pacific plate) moving over a "hot spot",
get out your favorite globe or world map and look at the Hawaiian islands.
The youngest island is Hawaii at the southern end of the chain (actually,
it's the undersea volcano Loihi just southeast of Hawaii).  The rest of the
chain of islands are progressively older as they trend northwest for
1,000 miles or so.  If you have a map or chart which details undersea
features, you can follow the remains of even older islands that are known
as the "Emperor Seamounts" for considerably further towards the northwest.
[Congratulations if you see a change of direction, the Pacific plate hasn't
always been moving in exactly the same way.]

-- 
Bob Cunningham
bob@hig.hawaii.edu