Newsgroup sci.geo.geology 36404

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In article ,
Charles Cagle  wrote:
>Using a fixed planet size in calculating the location of paleopoles has
>been one of the biggest mistake that researchers have made.  When this is
>done, a number of paleopole overshoots appear; 25 deg. for the Permian, 20
>deg. for the Triassic, 16 deg. for the Jurassic, 12 deg. for the
>Cretaceous, 6 deg. for the Miocene, 3.5 deg. for the Pliocene and 1.5
>degrees for the Pleistocene.
If these overshoots were consistent for all paleomagnetic observations
of a given age and decreased systematically through geologic time,
your (Carey's) objection would be much more persuasive.  As more and
better data become available this argument becomes less compelling.
>These anomalies are normally accounted for,
>according to Carey, by Paleomagneticians making ad hoc departures from
>their central dipole model of terrestrial magnetism.
A non-dipole component to the Earth's magnetic field isn't an
artifact of a model, it's an observed fact.  Note that today's
magnetic pole is about 13 degrees from the geographic pole.  The
precision of paleomagnetic results is limited by the non-dipole
component that's preserved in ancient samples.  The only practical
way to minimize this effect is to average the magnetic vectors from
samples that differ slightly in age.
-- 
    Chuck Karish          karish@mindcraft.com
    (415) 323-9000 x117   karish@pangea.stanford.edu

This is exactly what Viking attempted to do, and people argued
> over the results for years.  Did living organisms or zeolite clays effect
> the catalysis seen in the Viking results?  There are too many unknowns
> involved in remote experimentation of this nature.  If you send a package
> that looks for stereospecific amino acids and nothing else, how will you
> interpret a negative result?  Life based on other chemistries might still
> be present, or might once have been present.  The method of preparation
> used to obtain the sample from the soil by the robot might induce the
> loss of sterospecific structures.  Given our current results with poly-
> aromatic hydrocarbons from the ALH meteorite (*not* stereospecific as I
> recall), I don't think that we would gain much from yet more tinkering at
> the margins with questionable results from a one-shot experimental appar-
> atus 100,000,000 kilometers away.  It's much better at this point to bring
> the scientists and the rocks together, so that rigorous and flexible ex-
> periments can be performed.
> Unique ID : Ladasky, John Joseph Jr.
> Title     : BA Biochemistry, U.C. Berkeley, 1989  (Ph.D. perhaps 1998???)
> Location  : Stanford University, Dept. of Structural Biology, Fairchild D-105
> Keywords  : immunology, music, running, Green
Can we all keep our feet on the ground. 
Deep mining on Earth  for valuable resources is often economically
prohibited. 
Yet that is what is will be needed to find any more evidence on Mars
that is 
superior to the story that  ALH84001 has to tell. This is the most
informative 
object on Earth at the present time. 
	The analysis so far is good science, but this object needs to be
analyzed atom by atom, every electrical interaction, bonding forces,
gross structural integrity etc. needs to be recorded and explained.
So our first priority should be a complete upgrade to the JPL. Get some
of those toys Richard Zare has and spend the next 500 years analyzing
what impact events send our way.
The lets get real concept.
http://www.execulink.com/~louisew/chris.htm

Hello, I am a geology scientist. I am currenty working on water witching
techniques and radiestesy.. If you want to talk about this topic, please
write ...
Thanks a lot..
Ugur Ozgur 

In article <56bg1q$22g@cardinal1.Stanford.EDU> John Ladasky,
ladasky@leland.Stanford.EDU writes:
>I don't think that we would gain much from yet more tinkering at
>the margins with questionable results from a one-shot experimental appar-
>atus 100,000,000 kilometers away.  It's much better at this point to bring
>the scientists and the rocks together, so that rigorous and flexible ex-
>periments can be performed.
Agreed. But rather than send men there for a one-shot look-see, why not
send a robot rover to gather up a whole bunch of interesting samples from
the surface and ship them back. You could even design a robot which
crushes up or probes lots of possible rocks in search for carbon-bearing
types, and only ships back potentially interesting samples. Surely the
cost savings of not having to send people/food/air/water, and the fuel
needed to send them back and forth, would be immense. And we could
examine these bona fide Mars rocks at our leisure back here on Earth. 
Even the recent discoveries of potential martian fossils would never had
been made without the ability for protracted, thoughtful analysis of
meteorite samples found on earth, using bulky and expensive equipment
which was built for other purposes. The proposed fossils on Mars would
likely never have been found by an astronaut or two roving around on the
martian surface for a couple of days.
And all this assumes that a search for ancient life on Mars (the
atmosphere is not compatible with life today) is worth the billions it
would cost even for a low-budget sample retrieval mission, never mind the
astronomical cost of a manned mission. You seem to forget that we have
been unable to balance the federal budget since we decided to send a man
to the moon. Perhaps we should attempt such earthly goals before we start
sending men to other worlds to "see what's out there". Just a thought.
*******************************************************************
* S Krueger (skrueger@arco.com)          *                        *
* This message is personal and does not  *   This Sace For Rent   *
* reflect the opinions of my employer    *                        *
*******************************************************************

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steve eric cisna   wrote:
>> 
>> In article <32853A38.38E7@gte.net>, ashes@gte.net says...
>> >
>> >I read in a science book that there is a greater posibility of a
>> >printinng press exploding and forming webster's dictionary completly by
>> >accident; as opposed to the world being created from some dead matter.
>> 
>
>[...] I'm sure that the printing 
>press story does have about the same possibility as the earth exactly as 
>it is being formed.  But the way it is now is just one of many 
>possibilities.  It's just the one that happened.
  This is known as the anthropic principle.  Another way of looking at
it is to explode a printing press and see what comes out.  It won't 
be Webster's dictionary, but it will be something.  Take the result, 
hold it in your hand, and ask yourself "What is the probability of the 
exploding printing press giving exactly what I'm holding in my hand?".  
The answer is, of course, negligibly close to zero.  So, by this science
book's argument, what you're holding in your hand cannot therefore exist.
  The anthropic principle is a powerful argument, but it is easy to
abuse it.  Physicists -- I am reading this from sci.physics -- are often
asking "Why is such-and-such the way it is?".  The anthropic principle
is one way to answer the question (i.e. "if such-and-such weren't, then
we wouldn't be around to ask the question"), but there is often some
deeper connection that is waiting to be discovered.
  BTW, I have no feel for the absolute probability of an exploding
printing press producing Webster's dictionary, or for the creation of
the earth, so I can't judge the so-called science book's claim.  However, 
the book is implicitly asking the wrong question.  The question is not
what is the total probability of the earth being created from some dead
matter.  The correct question is, given the earth exists, what is the
conditional probability that it was created from some dead matter (just
what is "dead matter", anyway?).  The answer to the first question is
very small, whereas the answer to the second is very large.
    - Gordon
--
#include 
Gordon Long                      |  email: Gordon.Long@cern.ch
CERN/PPE                         |    
CH-1211 Geneva 23 (Switzerland)  |

Visiting Assistant Professor in Tectonics/University of Michigan. 
The Department of Geological Sciences invites applications for a
one-year
replacement position in Tectonics, starting September 1, 1997.  We
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a
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	Applicants must have completed a Ph.D. and preferably have one to two
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	Inquiries and applications, including a resume, a bibliography, a
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University of Michigan, 2534 C.C. Little Building
Ann Arbor, MI 48109-1063
email: vdpluijm@umich.edu; fax: (313) 763-4690
	Applications will be considered until the position is filled.
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------------------------------
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vdpluijm@umich.edu  -  http://www-personal.umich.edu/~vdpluijm

In article <328A9CFA.7118@worldnet.att.net>,
Melanie Roberti   wrote:
[...]
>> Personal views only.Wait! If the entire earths mass were concentrated as a shell, and you 
>>were to climb thru a hole and emerge on the inside, you would not have 
>>to wait until you reached the earths center before you were weightless. 
> You would be weightless as soon as you emerged thru the hole! There 
>would be no gravitational force experienced anywhere inside the inner 
>radius of the sphere.
To take this one step further, there is a zero field inside a spherical
shell of any type involving an inverse square field law. For instance,
the electrical field inside a charged spherical shell is zero.
This is a fairly elementary calculus problem.
The gravitaional field inside the earth is linear with respect to
radius, with a zero field at the center and reaching g at the surface.
-- 
    ********** DAVE HATUNEN (hatunen@netcom.com) **********
    *               Daly City California                  *
    *   Between San Francisco and South San Francisco     *
    *******************************************************

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Judson McClendon  wrote:
>> Judson McClendon wrote:
>> >
[big snip]
>So the God who created this vast universe, and us, has put up with a
>rebellious bunch of humans for thousands of years, watching us kill,
>steal, lie, cheat and so on.  So He sends His own Son Jesus to take our
>sins upon Himself and die a horrible death on a Roman cross to pay the
>penalty for those sins.  Then He tells us that all we have to do is
>believe on Jesus and receive Him as Savior and Lord and God will
>completely forgive us all our sins and give us eternal life as a
>reward.  And you call that God a 'kill-joy'.
>-- 
Judson, god hasn't told *me* anything of the sort! If your post,
including the snip, were to have "God" replaced with ET, you would be
judged insane by many people. Myths hold no compulsion with me.
Slim
>Judson McClendon
>Sun Valley Systems    judsonmc@ix.netcom.com
Beowulf     How ceaselessly Grendel harassed.....

hatunen@netcom.com (DaveHatunen) writes:
>In article <328A9CFA.7118@worldnet.att.net>,
>Melanie Roberti   wrote:
>[...]
>To take this one step further, there is a zero field inside a spherical
>shell of any type involving an inverse square field law. For instance,
>the electrical field inside a charged spherical shell is zero.
>This is a fairly elementary calculus problem.
yeah, think Gauss' Law. Works for gravity, electricity..makes my life easier
for sure.
The reason the shell outside the radius you're standing on cancels is because
you have exactly that much opposite you (thru the earth's center) that cancels
out what's above you, so that the only difference is what is between you and
the center.
>The gravitaional field inside the earth is linear with respect to
>radius, with a zero field at the center and reaching g at the surface.
-- 
Katishna J. King  *  University of Oklahoma Geophysics  *  kate@ou.edu
I'm ECN's Student Unix Tech, not their spokesperson!
Cavendish weighed his balls, using Earth as a wedgie! -- B. Hutchings
Witches use brooms because nature abhors a vacuum. -- P. Michaelson

Manley Hubbell (Manley.Hubbell@hubert.rain.com) wrote:
: hmm?  well i notice the Question about the future of Geology
: and i think there`s some basic truth in the question
:    anyway on an inquiry to Lewis & Clark  here in the Portland (Or) 
: area i was surprised to find that they do NOT even teach Geology
: hmm?  and i suspect that enrolement in Geology classes have been
: declining in many universities   ... maybe its a given  T-REXX
:  was  and`s no more  ? 
Manley, might I suggest paying a bit more attention to your grammar - 
it makes things much easier to read.  As for Lewis&Clark;, isn't that 
one of those itty-bitty liberal arts colleges where anything 
scientific is kind of suspect?  When I was looking at graduate 
schools, I found a solid program at Portland State University...
Personally, I'm sure that there will always be a need for geologist 
types, but you can argue endlessly about the numbers needed.
Cheers,
Jim 

In Article <56du23$pag@news.Hawaii.Edu>, gerard@hawaii.edu (Gerard Fryer) wrote:
>
>In article , singtech@teleport.com
(Charles Cagle) writes:
>
>>Using a fixed planet size in calculating the location of paleopoles has
>>been one of the biggest mistake that researchers have made.  When this is
>>done, a number of paleopole overshoots appear; 25 deg. for the Permian, 20
>>deg. for the Triassic, 16 deg. for the Jurassic, 12 deg. for the
>>Cretaceous, 6 deg. for the Miocene, 3.5 deg. for the Pliocene and 1.5
>>degrees for the Pleistocene.   These anomalies are normally accounted for,
>>according to Carey, by Paleomagneticians making ad hoc departures from
>>their central dipole model of terrestrial magnetism.   There would likely
>>be no overshoots if one but realized that the angular distances on a
>>smaller earth get progessively larger as the planet grows.  It is
>>presumptive to assess the data from the viewpoint that the earth hasn't
>>expanded when it has and think to shove aside the anomalies which appear
>>by such sloppy processes.
>
>Naturally if you invoke another parameter, such as variable Earth
>radius, you can fit data better. If you keep adding adjustable
>parameters you'll fit the data better and better, but will you be
>learning anything? The reason so many people resist the expanding Earth
>idea is that they see no compelling reason to adopt it. Admittedly
>Occam's Razor is too often invoked in science, especially in geology
>(some nice words about this were in a recent Economist), but most
>scientists still think that in the absence of other information you
>should choose the most parsimonious parameterization you can.
>
>As for departures from a dipole field, paleomagneticians are forced
>into this only during polarity reversals (and only then when time
>sampling is dense enough to catch a reversal in action).
>
This is usually the sort of thread I stay away from, but there's problems in
both the original comment and reply that I have a little trouble with.
First, the reply.  The problem with overshoots was indeed real and of some
concern for some time.  Much of it came from a greater confidence in the
data than was warranted.  Paleomag is unusually heavy on statistics for a
geological enterprise; what these statistics will always miss, though, are
systematic biases.  Three such biases (that I remember) have wormed their
way into many paleopoles, particularly older poles obtained at the time
Carey was making these comments.  First, sedimentary rocks will frequently
have a flattening caused by sediment compaction; this tends to flatten the
magnetic inclination (a number of Miocene paleopoles in southern California
probably suffer from this).  Second, volcanic rocks sample the geomagnetic
field very quickly, thus including secular variation of the field.  If you
sample enough volcanics, and there are not serious problems with episodic
volcanism, this is not a problem, but if you do not, you are adding in some
non-dipole field.  On average, this will shallow inclinations (meaning you
get paleopole overshoot) simply because there is a smaller percentage of
directions that is steeper than is shallower (except near the equator, where
very little pmag comes from).  Third, viscous remagnetization is a real
problem.  A number of localities, particularly of older (Paleozoic) rocks,
were found in the early 80s to have been overprinted with a later
remagnetization.  Many other sites have a similar problem, although the
original field is not obliterated, it is obscured.  Again, these overprints
are frequently relatively random (depends on the exact circumstance) and
will tend, statistically, to shallow inclinations and thus produce an
overshoot.  Because viscous remagnetization increases with time, older
samples are more likely to be contaminated and thus overshoot a greater
problem farther into the past.
More recent paleomag has been scrutenized more carefully, and classic
localities have been resampled.  Arguments continue over the validity of
individual sites and how to compile data, but by and large these problems
are difficulties in measuring ancient magnetizations and not problems with
earth diameter.
Which brings me back to the original suggestion that overshoot reflects
Earth expansion.  I think this is quite wrong--let me outline my logic and
see if I have a mental blunder.  Imagine a continent at the equator through
a long period.  Paleomag from sites on the equator will show the pole being
90 degrees away all along, whether the Earth expands or not.  Thus nothing
there to measure the Earth's diameter.  Sites on the same continent at, say,
30 degrees north today would have been at higher latitudes in the past on an
expanding Earth, no?  So their paleoinclinations would have been *greater*
than today--not shallower, and the paleopoles would be on the near side,
*not* the far side of the modern pole.  This is the *opposite* of the
problem that was discussed above; thus if anything the bias in the paleomag
would argue for a contracting Earth!
The problem, I believe, was some misunderstanding somewhere that paleomag
was measuring a linear distance, when in fact it is an angular distance. 
Perhaps overshoot was misunderstood somewhere.  If I've made a blunder, let
me know, but I'm pretty sure this is right.
Craig Jones                                    cjones@mantle.colorado.edu
      Research Associate, CIRES, University of Colorado, Boulder
WWW: http://cires.colorado.edu/people/jones.craig/CHJ_home.html

Terry Pundiak  wrote:
>Sorry, if this posting is totally ridiculous... I am a science advocate 
>but geology is not my forte.
>Somewhere recently I saw someone write that there was less gravity as 
>one got closer to the center of the earth than on the surface, because 
>there was less matter ahead as much was already behind, and at the 
>center matter is all around you.   I always think in terms of center of 
>mass, but in this case that may be wrong.
>Is this true?  If it is then all sorts of crazy things could be 
>happening.   The outer hard shell could be locked in place like a stone 
>arch.   There is no pressure under a stone arch. So like a large 
>spherical stone arch there could be less gravitational pressure deeper 
>in the earth... then at the center would there be gravitational pressure 
>in all directions?  
> 
>I am sure this is a crazy thing but can someone steer me right, I may 
>sleep better.
>Terry Pundiak
Forgive me if I am passing along incorrect information but as far as I
know gravitational attraction can still be defined by  Newton's law: 
F=G(m1*m2)/r^2
where F is the gravitational force exerted on an object, G is the
gravitational constant, m1 is the mass of one body and m2 is the mass
of the other, with r being the distance between them.  Thus, as r (the
distance between them) becomes smaller (approaching the center of the
earth) the gravitational force becomes stronger.  I believe this is
the reasoning that is used to describe the generation of fusion
reactions in the sun.  That is that the attraction between the
particles of the sun become great enough at some depth below the
surface to produce the heat necessary to start the reaction.  
In regards to your stone arch analogy unless someone changed plate
tectonic theory the outer "hard" shell of the earth is actually
thought to be 'floating' on a semi-liquid layer called the
asthenosphere where there are no supports for your so called arch.  In
fact the theory suggests that at rift zones the plates are actually
pulling apart which would not allow an arch such as described to form.
I hope this doesn't cause more confusion. Kevin

In article ,
S Krueger   wrote:
>In article <56bg1q$22g@cardinal1.Stanford.EDU> John Ladasky,
>ladasky@leland.Stanford.EDU writes:
>>I don't think that we would gain much from yet more tinkering at
>>the margins with questionable results from a one-shot experimental appar-
>>atus 100,000,000 kilometers away.  It's much better at this point to bring
>>the scientists and the rocks together, so that rigorous and flexible ex-
>>periments can be performed.
>
>Agreed. But rather than send men there for a one-shot look-see, why not
>send a robot rover to gather up a whole bunch of interesting samples from
>the surface and ship them back.
	Notice that I said "bring the scientists and the rocks together."  
I did not specify whether Mohammed would go to the mountain or vice versa.
In an earlier post in this thread, I expressed support for a sample-retrieval
robot.
>You could even design a robot which
>crushes up or probes lots of possible rocks in search for carbon-bearing
>types, and only ships back potentially interesting samples. Surely the
>cost savings of not having to send people/food/air/water, and the fuel
>needed to send them back and forth, would be immense. And we could
>examine these bona fide Mars rocks at our leisure back here on Earth. 
	I'm waiting with interest for the results from the Russian "golf
tee" probes that are expected to penetrate into the Martian soil.
>Even the recent discoveries of potential martian fossils would never had
>been made without the ability for protracted, thoughtful analysis of
>meteorite samples found on earth, using bulky and expensive equipment
>which was built for other purposes. The proposed fossils on Mars would
>likely never have been found by an astronaut or two roving around on the
>martian surface for a couple of days.
	But if we bother to send humans to Mars, a trip which would take
several months each way, we surely wouldn't spend a mere few days on the
surface.  A month, at least?  If we send some equipment that allows for
preliminary analyses, we would probably get a better feel for where to 
look for more evidence.
>And all this assumes that a search for ancient life on Mars (the
>atmosphere is not compatible with life today) is worth the billions it
>would cost even for a low-budget sample retrieval mission, never mind the
>astronomical cost of a manned mission. You seem to forget that we have
>been unable to balance the federal budget since we decided to send a man
>to the moon. Perhaps we should attempt such earthly goals before we start
>sending men to other worlds to "see what's out there". Just a thought.
	Err, no, I haven't forgotten about the federal budget.  (Aside -
is scientific research a primary, or even secondary, cause of the budget
crisis?  *Hardly.*)  But I can think of a lot of places to get, say, $50
billion over the next ten years that would not bust the budget.  This is
only a fraction of the present NASA budget.  And with the international
cooperation that everyone says will be required to fund a Mars mission,
we should be able to double this, at least.
-- 
Unique ID : Ladasky, John Joseph Jr.
Title     : BA Biochemistry, U.C. Berkeley, 1989  (Ph.D. perhaps 1998???)
Location  : Stanford University, Dept. of Structural Biology, Fairchild D-105
Keywords  : immunology, music, running, Green

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hatunen@netcom.com (DaveHatunen) wrote:
>To take this one step further, there is a zero field inside a spherical
>shell of any type involving an inverse square field law. For instance,
>the electrical field inside a charged spherical shell is zero.
>
>This is a fairly elementary calculus problem.
>
>The gravitational field inside the earth is linear with respect to
>radius, with a zero field at the center and reaching g at the surface.
>
The latter statement would be true for a homogeneous earth or any
sphere with a homogenous density. However, the earth's nickel/iron
core has a higher density than the average density of the earth so
gravity would not vary in a perfectly linear fashion in the real
earth.
Richard B. Winston
Dept. of Geology and Geophysics		rwinsto@lsuvm.sncc.lsu.edu
Louisiana State University	http://aapg.geol.lsu.edu/rbwinsto.htm
Baton Rouge, La 70803		ftp://aapg.geol.lsu.edu/pub/winston
U.S.A.
504-388-2337
Fax 504-388-2302

In article <328A9CFA.7118@worldnet.att.net>, Melanie Roberti
, in response to my bunch of codswallop,
wrote:
>
>Wait! If the entire earths mass were concentrated as a shell, and you 
>were to climb thru a hole and emerge on the inside, you would not have 
>to wait until you reached the earths center before you were weightless. 
> You would be weightless as soon as you emerged thru the hole! There 
>would be no gravitational force experienced anywhere inside the inner 
>radius of the sphere.
Duh! You are absolutely right, of course. The crazy thing is that this
isn't the first time I have made this mistake. I got it wrong in my comprehensives too. So that's why I was having feelings of deja vu...
-- 
Gerard Fryer      
gerard@hawaii.edu        http://www.soest.hawaii.edu/~gerard/
Personal views only.

In a previous article, kate@mailhost.ecn.uoknor.edu (Katishna King) says:
>hatunen@netcom.com (DaveHatunen) writes:
>>The gravitaional field inside the earth is linear with respect to
>>radius, with a zero field at the center and reaching g at the surface.
ah, that's just what I was looking for;
the assumption is the same as for water!
-- 
You *don't* have to be a rocket scientist.  (College Career Counselor
					     to me, again )
There is no dimension without time.  --RBF (Synergetics, 527.01)

IG (Slim) Simpson wrote:
> 
> Judson McClendon  wrote:
> 
> >> Judson McClendon wrote:
> [big snip]
> >So the God who created this vast universe, and us, has put up with a
> >rebellious bunch of humans for thousands of years, watching us kill,
> >steal, lie, cheat and so on.  So He sends His own Son Jesus to take our
> >sins upon Himself and die a horrible death on a Roman cross to pay the
> >penalty for those sins.  Then He tells us that all we have to do is
> >believe on Jesus and receive Him as Savior and Lord and God will
> >completely forgive us all our sins and give us eternal life as a
> >reward.  And you call that God a 'kill-joy'.
> 
> Judson, god hasn't told *me* anything of the sort! If your post,
> including the snip, were to have "God" replaced with ET, you would be
> judged insane by many people. Myths hold no compulsion with me.
Romans 1:18-32:
18 For the wrath of God is revealed from heaven against all
ungodliness and unrighteousness of men, who suppress the truth in
unrighteousness,
19 because what may be known of God is manifest in them, for God has
shown it to them.
20 For since the creation of the world His invisible attributes are
clearly seen, being understood by the things that are made, even His
eternal power and Godhead, so that they are without excuse,
21 because, although they knew God, they did not glorify Him as God,
nor were thankful, but became futile in their thoughts, and their
foolish hearts were darkened.
22 Professing to be wise, they became fools,
23 and changed the glory of the incorruptible God into an image made
like corruptible man-- and birds and four-footed animals and creeping
things.
24 Therefore God also gave them up to uncleanness, in the lusts of
their hearts, to dishonor their bodies among themselves,
25 who exchanged the truth of God for the lie, and worshiped and
served the creature rather than the Creator, who is blessed forever.
Amen.
26 For this reason God gave them up to vile passions. For even their
women exchanged the natural use for what is against nature.
27 Likewise also the men, leaving the natural use of the woman, burned
in their lust for one another, men with men committing what is
shameful, and receiving in themselves the penalty of their error which
was due.
28 And even as they did not like to retain God in their knowledge, God
gave them over to a debased mind, to do those things which are not
fitting;
29 being filled with all unrighteousness, sexual immorality,
wickedness, covetousness, maliciousness; full of envy, murder, strife,
deceit, evil-mindedness; they are whisperers,
30 backbiters, haters of God, violent, proud, boasters, inventors of
evil things, disobedient to parents,
31 undiscerning, untrustworthy, unloving, unforgiving, unmerciful;
32 who, knowing the righteous judgment of God, that those who practice
such things are worthy of death, not only do the same but also approve
of those who practice them.
-- 
Judson McClendon
Sun Valley Systems    judsonmc@ix.netcom.com

>> Well, here comes: is pegmatite (in Spanish: pegmatita) a plutonic
>> (in Spanish: plutonica) or a metamorphic (in Spanish: metamorfica) rock?
According to the American Geological Institute dictionary:
Pegmatite:  Those igneous rocks of course grain found usually as dikes 
associated with a large mass of plutonic of finer grain size.

Kevin Wilson wrote:
> 
> Terry Pundiak  wrote:
> 
> >Sorry, if this posting is totally ridiculous... I am a science advocate
> >but geology is not my forte.
> 
> >Somewhere recently I saw someone write that there was less gravity as
> >one got closer to the center of the earth than on the surface, because
> >there was less matter ahead as much was already behind, and at the
> >center matter is all around you.   I always think in terms of center of
> >mass, but in this case that may be wrong.
> 
> >Is this true?  If it is then all sorts of crazy things could be
> >happening.   The outer hard shell could be locked in place like a stone
> >arch.   There is no pressure under a stone arch. So like a large
> >spherical stone arch there could be less gravitational pressure deeper
> >in the earth... then at the center would there be gravitational pressure
> >in all directions?
> >
> >I am sure this is a crazy thing but can someone steer me right, I may
> >sleep better.
> >Terry Pundiak
> Forgive me if I am passing along incorrect information but as far as I
> know gravitational attraction can still be defined by  Newton's law:
> F=G(m1*m2)/r^2
> where F is the gravitational force exerted on an object, G is the
> gravitational constant, m1 is the mass of one body and m2 is the mass
> of the other, with r being the distance between them.  Thus, as r (the
> distance between them) becomes smaller (approaching the center of the
> earth) the gravitational force becomes stronger.  I believe this is
> the reasoning that is used to describe the generation of fusion
> reactions in the sun.  That is that the attraction between the
> particles of the sun become great enough at some depth below the
> surface to produce the heat necessary to start the reaction.
> In regards to your stone arch analogy unless someone changed plate
> tectonic theory the outer "hard" shell of the earth is actually
> thought to be 'floating' on a semi-liquid layer called the
> asthenosphere where there are no supports for your so called arch.  In
> fact the theory suggests that at rift zones the plates are actually
> pulling apart which would not allow an arch such as described to form.
> I hope this doesn't cause more confusion. Kevin
Ah! Your analysis that the gravitational attraction becomes greater as 
the distance of seperation becomes smaller is only valid until you reach 
the surface of the earth. Note that according to F=G(m1*m2)/r^2 that m2, 
the mass of the earth which contributes to the gravitational attraction 
becomes smaller and smaller as you  approach the earths  
center.  This is because the mass of the 'shell' of earth lying above 
you can no longer be included in the calculation for m2.  Even though 
the gravitational attraction increases whith the square oyour distance 
from the center of the earth, the contribution of m2 (the earth mass 
remaining inside the smaller radious) decreases with the cube of the 
radius to the center (assuming a uniform density) of corse at the center 
of the earth the gravitational attraction is zip, nada, zero.  The part 
that everybody is finding objectionable here is that they no that there 
are enormous pressures at the earths center, it just seems right! Well 
the fact that the gravitational force decreases with depth in no way 
diminishes this fact.

In article <328c88ca.9701512@te6000.otc.lsu.edu>,
Richard B. Winston  wrote:
>hatunen@netcom.com (DaveHatunen) wrote:
>
>>To take this one step further, there is a zero field inside a spherical
>>shell of any type involving an inverse square field law. For instance,
>>the electrical field inside a charged spherical shell is zero.
>>
>>This is a fairly elementary calculus problem.
>>
>>The gravitational field inside the earth is linear with respect to
>>radius, with a zero field at the center and reaching g at the surface.
>>
>
>The latter statement would be true for a homogeneous earth or any
>sphere with a homogenous density. However, the earth's nickel/iron
>core has a higher density than the average density of the earth so
>gravity would not vary in a perfectly linear fashion in the real
>earth.
Ah, yes. Of course. I negelcted to add "for a sphere of uniform
density". But lest anyone take this to mean something it doesn't, as
long as you have density that is constant on any given spherical shell,
the field at the center is still zero.
-- 
    ********** DAVE HATUNEN (hatunen@netcom.com) **********
    *               Daly City California                  *
    *   Between San Francisco and South San Francisco     *
    *******************************************************

Melanie Roberti wrote:
> A particle within the earth at  some radial distance from the earths
> center would experience the gravitational force due only to the mass of
> earth which is inside that radius.  At the center, there is no remaining
... SNIP ...
> earths radius, the gravitational force would decrease in proportion
> whith the square of the distance from the earths center.  The earth is
> not of uniform density, but that doesn't change the conclusion that at
> the center of the earth there is no gravitational force.
Wouldn't it be technically more correct to say that the gravitational
force vectors exerted on a particle at the center of the earth are in
equilibrium and sum to a zero accelaration vector?  There is
gravitational force exerted on a particle there but in that reference
frame there is no acceleration vector due to it.
Steve Michnick
UNIX Shepherd
MEPTEC

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In article <328c88ca.9701512@te6000.otc.lsu.edu>, rwinsto@lsuvm.sncc.lsu.edu (Richard B. Winston) writes:
>hatunen@netcom.com (DaveHatunen) wrote:
>>The gravitational field inside the earth is linear with respect to
>>radius, with a zero field at the center and reaching g at the surface.
>>
>
>The latter statement would be true for a homogeneous earth or any
>sphere with a homogenous density. However, the earth's nickel/iron
>core has a higher density than the average density of the earth so
>gravity would not vary in a perfectly linear fashion in the real
>earth.
Ha! A chance to redeem myself for my earlier blunder.
In an Earth of constant density g would indeed be proportional to
radius r so you would get a linear decrease in g from the surface to
the center. But the Earth is not of constant density - density changes
because of self-compression (the weight of everything above squeezes
the rock). That alone would mean that there would be some depth in the
Earth at which g is a maximum. In fact mass is concentrated in the core
of the Earth, so the way g varies with depth is to stay pretty constant
with depth until you start to get near the bottom of the mantle, then g
rises to a maximum of about 11m/(s**2) at the core-mantle-boundary.
Below that g decreases almost linearly to zero at the Earth's center.
-- 
Gerard Fryer      
gerard@hawaii.edu        http://www.soest.hawaii.edu/~gerard/
Personal views only.