Coming soon to a newgroup near you.

J. Taylor wrote:


Robin Levett wrote:
J. Taylor wrote:


Robin Levett wrote:
J. Taylor wrote:


Robin Levett wrote:
J. Taylor wrote:


Robin Levett wrote:
J. Taylor wrote:


Robin Levett wrote:
J. Taylor wrote:


Robin Levett wrote:
J. Taylor wrote:


Robin Levett wrote:
don findlay wrote:


Timberwoof wrote:

You are lying. You've been told many times in this
thread by qualified geologists and others that
subduction is not the driving force for plate
tectonics, but that mantle convection is.
Nevertheless, you go on
presenting that false version of plate tectonics as
a straw man to easily tear down.

Yes, ..and here it is again:-

Professor Seiya Uyeda (Tokai University, Japan), a
world-renowned expert in plate tectonics, concluded
in his keynote address at a major scientific
conference on subduction processes in June 1994 that
"subduction . . . plays a more fundamental role than
seafloor spreading in shaping the earth's surface
features" and "running the plate tectonic machinery."
The gravity-controlled sinking of a cold, denser
oceanic slab into the subduction zone (called "slab
pull") -- dragging the rest of the plate along with
it -- is now considered to be the driving force of
plate tectonics."
http://pubs.usgs.gov/gip/dynamic/unanswered.html


Whatever your "qualified geologists" are qualified
in, it's certainly not Plate Tectonics.

Let's put that quotemine in context:-

"What drives the plates?

From seismic and other geophysical evidence and
laboratory experiments, scientists generally agree with
Harry Hess' theory that the plate-driving force is the
slow movement of hot, softened mantle that lies below
the rigid plates. This idea was first considered in the
1930s by Arthur Holmes, the English geologist who later
influenced Harry Hess' thinking about seafloor
spreading. Holmes speculated that the circular motion
of the mantle carried the continents along in much the
same way as a conveyor belt. However, at the time that
Wegener proposed his theory of continental drift, most
scientists still believed the Earth was a solid,
motionless body. We now know better. As J. Tuzo Wilson
eloquently stated in 1968, "The earth, instead of
appearing as an inert statue, is a living, mobile
thing." Both the Earth's surface and its interior are
in motion. Below the lithospheric plates, at some depth
the mantle is partially molten and can flow, albeit
slowly, in response to steady forces applied for long
periods of time. Just as a solid metal like steel, when
exposed to heat and pressure, can be softened and take
different shapes, so too can solid rock in the mantle
when subjected to heat and pressure in the Earth's
interior over millions of years.

The mobile rock beneath the rigid plates is believed to
be moving in a circular manner somewhat like a pot of
thick soup when heated to boiling. The heated soup
rises to the surface, spreads and begins to cool, and
then sinks back to the bottom of the pot where it is
reheated and rises again. This cycle is repeated over
and over to generate what scientists call a convection
cell or convective flow. While convective flow can be
observed easily in a pot of boiling soup, the idea of
such a process stirring up the Earth's interior is much
more difficult to grasp. While we know that convective
motion in the Earth is much, much slower than that of
boiling soup, many unanswered questions remain: How
many convection cells exist? Where and how do they
originate? What is their structure?

Convection cannot take place without a source of heat.
Heat within the Earth comes from two main sources:
radioactive decay and residual heat. Radioactive decay,
a spontaneous process that is the basis of "isotopic
clocks" used to date rocks, involves the loss of
particles from the nucleus of an isotope (the parent)
to form an isotope of a new element (the daughter). The
radioactive decay of naturally occurring chemical
elements -- most notably uranium, thorium, and
potassium -- releases energy in the form of heat, which
slowly migrates toward the Earth's surface. Residual
heat is gravitational energy left over from the
formation of the Earth -- 4.6 billion years ago -- by
the "falling together" and compression of cosmic
debris. How and why the escape of interior heat becomes
concentrated in certain regions to form convection
cells remains a mystery.

Until the 1990s, prevailing explanations about what
drives plate tectonics have emphasized mantle
convection, and most earth scientists believed that
seafloor spreading was the primary mechanism. Cold,
denser material convects downward and hotter, lighter
material rises because of gravity; this movement of
material is an essential part of convection. In
addition to the convective forces, some geologists
argue that the intrusion of magma into the spreading
ridge provides an additional force (called "ridge
push") to propel and maintain plate movement. Thus,
subduction processes are considered to be secondary, a
logical but largely passive consequence of seafloor
spreading. In recent years however, the tide has
turned. Most scientists now favor the notion that
forces associated with subduction are more important
than seafloor spreading. Professor Seiya Uyeda (Tokai
University, Japan), a world-renowned expert in plate
tectonics, concluded in his keynote address at a major
scientific conference on subduction processes in June
1994 that "subduction . . . plays a more fundamental
role than seafloor spreading in shaping the earth's
surface features" and "running the plate tectonic
machinery." The gravity-controlled sinking of a cold,
denser oceanic slab into the subduction zone (called
"slab pull") -- dragging the rest of the plate along
with it -- is now considered to be the driving force of
plate tectonics."


Note the first sentence of the full page. It is true
that Uyeda is pointing out that subduction is more
important than seafloor spreading; but he is not
dealing with the fundamental issue of convection.


Then you will be surprised to read the below, which
compares the two directly.

Also provided the link to the full article so you cannot
make it out to be quote mining


BEGIN *****
http://www.umich.edu/~gs265/tecpaper.htm

Discussion and Conclusion

To the question, "What drives plate tectonics?" we have
presented two options: (1) mantle convection, and (2)
lithospheric plate boundary and body forces. It is in
the opinion of this author that it is the plates
themselves that are the dominant source of force
involved in the absolute movement of the lithospheric
plates over the surface of the Earth. The strong
correlations between observed tectonic stress and
absolute plate motions shown by the World Stress Map
Project point directly to the present lithospheric
stress fields being dominated by the individual plate
boundary and body forces (Zoback et al., 1989, Zoback,
1992). These observations, along with the Net Torque
Model, allow us to begin to put a coherent story
together in terms of the relative magnitudes of
different PDF's. Although the slab forces (slab pull and
collisional resistance) dominate the other PDF's, their
equal and opposite nature allows ridge push to be the
most important observable plate driving force.

END ****

Except that that isn't the end, is it? The final two
sentences a-

"So, in a sense, it is because of the present condition
that we have today's magnitudes and effective forces, and
through time the dominant forces will change from plate to
mantle and back. After all, is it not the mantle itself
that inevitably supplies the energy and heat that runs the
system?"


Which sounds exactly like a saving grace position beyond
the bounds of what is found in the paper and therefore
unknowable, but it does give comfort for shattered beliefs.

Unlikely, since he also uses the following quote at the foot
of the page:-

Yes, precisely, thus the reason for the quote to bolster the
spirit of the faithful.

No; to put the paper in context.




"Plates could not move, or even exist, if not for the Earth's
heat which must be removed from its interior to the surface
through mantle convection. In this sense the mantle drives
the plates, for it is the interior of the Earth that is the
ultimate source of energy of all motion."

In other words, never mind convection is no longer the
dominant driver, it is still holds an important place in our
hearts, if not our minds.


Explain how, without mantle convection, slab pull can drive
plate tectonics. Mantle convection puts the energy into the
system; slab pull is the immediate mechanism.


Robin,

I am not saying it can, and if slab pull is the dominate driver
some how we are now getting more energy out than what was put in.

Incorrect.

Have you read the rest of the USGS site on the topic; or have you
just cherry-picked this page?


And you are talking about what?

You post trying to give the impression the link Findlay posted from
USGS said something different than what it did.

I merely provided the full context, whence it was clear that the
author was actually, in that cite, talking about the relative
contributions of slab pull and ridge push.


I posted this link, http://www.umich.edu/~gs265/tecpaper.htm, which
specifically stated, it was slab pull NOT convection which is the
driver.

And ignored the fact that the author of the page specifically stated
that convection supplies the energy, dismissing the comment as simply
to bolster the spirits of the faithful.

The word energy is used three times and none of them say "convection
supplies the energy"

"(4) provide enough energy to account for all the motion"

From the paragraphs:-

"WHAT Drives Plate Tectonics ???? This question has been the subject of
intense debate ever since the plate tectonic theory was first eccepted by
the geologic community in the late 1960's. The major concern is whether
mantle convection and the activity of mantle plumes dominate the driving
forces of plate motion, or whether surface boundary and plate forces,
such as slab pull and ridge push provide the most important forces. The
argument is basically whether the plates are passively riding along on
the top of a mantle convection cell, or whether the plates themselves the
active drivers, dragging along with them the mantle below.


To begin understanding and evaluating the different forces involved in
the plate tectonic process, we must first isolate these forces and define
their physical and mechanical properties. Once we have done that, we must
make sure that any hypothesis or model that we devise to produce these
forces is compatible with the observations and characteristics that we
know and understand about the Earth. Mainly, is the model (1) compatible
with the rigid behavior of lithospheric plates, (2) compatible with the
wide variety of plate sizes, geometry, type, and motion; does it (3)
satisfy the existence of complex plate boundary conditions, (4) provide
enough energy to account for all the motion; is it able to (5) produce
the observed tectonic stresses observed in the upper lithosphere; and
does it (6) satisfy the long-lived steady state relative plate motions
(on the order of tens of millions of years), as well as sudden dramatic
changes in motion we observe from modeled plate reconstructions (i.e.,
the Pacific plate circa 43 Ma). "


"....the mantle itself that inevitably supplies the energy and
heat...."

From:-
"There are still many unanswered questions related to PDF's. Can plate
driving forces be responsible for the breakup of supercontinents? Are
plate boundary and/or plate body forces responsible for the initiation of
subduction zones and spreading ridges? Most researchers believe in these
special cases, mantle forces related to large convection cells must
dominate the driving forces (Jacoby, 1980; Carlson et al, 1983;Wilson,
1991; Zeigler, 1991). So, in a sense, it is because of the present
condition that we have today's magnitudes and effective forces, and
through time the dominant forces will change from plate to mantle and
back. After all, is it not the mantle itself that inevitably supplies the
energy and heat that runs the system?"


"....interior of the Earth that is the ultimate source of energy of all
motion."

From the paragraph:-

"Plates could not move, or even exist, if not for the Earth's heat which
must be removed from its interior to the surface through mantle
convection. In this sense the mantle drives the plates, for it is the
interior of the Earth that is the ultimate source of energy of all
motion."


So I could not have ignored it. It simply is not there!

Ah, there's your problem; you have read the paragraphs after quote-mining
them, not before. Read the whole of the relevant paragraphs in each
case. You'll note that the energy refererd to is the heat removed from
the Earth's interior to the surface through mantle convection.

Oh yes, of course, I can see my error now. He really meant mantle
convection was the driving force when he most definitely said it was
not!

Funnily enough, you've got it wrong again. MC provides the energy for the
process. It lifts the hot new material to the surface, and drives the
motion of the convection cells.


You really should do something about that drinking problem.

What drinking problem?

Perhaps
not read under the influence.

Well, I'd certainly like to have something of whatever you were on when you
read about dark matter; I notice that my reference to your idea on this
appears to have been accidentally snipped without marking.

How's about we discuss how dark matter supplied the mass for an expanding
earth - you could reply to my post in the other thread, and we could then
go on from there.

--
Robin Levett
(unmunge by removing big blue - don't yahoo)