Examining the "physics" in geophysics

[gentleman-farmer]

I'm a new member - originally from Michigan and now in the land of hurricanes and alligators with my wife of many years, and our two horses. One's an Arab and the other is a dual registered Paint and Missouri Fox-trotter who thinks he's an Indian pony.

 

One might suggest that the title I've selected Examining the "physics" in geophysics belongs in another section - but it's the physics that I want to discuss - not the "geo."

 

An article appeared on CNN.com not long ago that discusses the issue, stating ::

"..U.S. students placed below average in both math and science.

 

http://cnnwire.blogs.cnn.com/2009/08/25/u-s-students-fall-behind-international-counterparts-in-math-science-analysis-says/

 

Here (in part is why) :: One of the major tenets advanced by geophysics is that flowing magma propels the plates and causes oceanic plate separation at the mid-ocean ridges. But magma (by definition - being molten, fully expanded - having gone through phase change) has no means, in itself, to move an inch. It is incapable of performing work (force through a distance), except in the formation stage when it is expanding and going through phase change.

 

Magma, by all definition, is a dead by-product of the heat that formed it.

 

Our young are entering the stages of advanced education with the notion of magma propelling plates firmly set in their minds. One might ask further -how it is that the physical interlocks that exist at plate boundaries (and the friction from movement) - never enter the equation?

 

Comments are welcome

 

gf

/

[swansont]

One might suggest that the title I've selected Examining the "physics" in geophysics belongs in another section - but it's the physics that I want to discuss - not the "geo."

 

An article appeared on CNN.com not long ago that discusses the issue, stating ::

 

http://cnnwire.blogs.cnn.com/2009/08/25/u-s-students-fall-behind-international-counterparts-in-math-science-analysis-says/

 

I'm guessing that the scenario of the students knowing the right answer but the test writer's answer being wrong isn't the cause of this.

 

 

Here (in part is why) :: One of the major tenets advanced by geophysics is that flowing magma propels the plates and causes oceanic plate separation at the mid-ocean ridges. But magma (by definition - being molten, fully expanded - having gone through phase change) has no means, in itself, to move an inch. It is incapable of performing work (force through a distance), except in the formation stage when it is expanding and going through phase change.

 

Magma, by all definition, is a dead by-product of the heat that formed it.

 

 

At the place where the phase change occurs, if there is expansion, how will it expand? By pushing on the surrounding materials, causing them to move. The magma near the surface doesn't have to be doing any work, by itself. Similar to turning on a hose — the source of the pressure causing the flow is at the spigot, not the nozzle.

[gentleman-farmer]

Let me restate the original premise. The geophysical claim is that magma propels the plates by what is said to be conveyor belts. I am stating (that is not possible) and violates the laws of physics as magma has exhausted all opportunity to perform work on initial formation. Any movement beyond the source must be the result of extrusion by newly formed material. Hence conveyor belts do not possess a motive force to maintain the system

 

Something else - way beyond conveyor belts is at work here

 

gf

/

[swansont]

I'm saying your premise doesn't violate the laws of physics. You push on one end of something (especially for a solid or an incompressible fluid), the other end moves. As long as you are continually melting rock, you have expansion to move the magma. The force is transmitted through the fluid. It does not need to be created by the fluid.

[gentleman-farmer]

swansont

I'm saying your premise doesn't violate the laws of physics. You push on one end of something (especially for a solid or an incompressible fluid), the other end moves. As long as you are continually melting rock, you have expansion to move the magma. The force is transmitted through the fluid. It does not need to be created by the fluid

 

gf) I disagree with your analysis. The surface of the earth is 196,940,400 square miles - (and the plates cover the entire surface) how far do you figure on pushing this cooling mass of magma? Better yet - you have to provide the proof that this magma never cools otherwise it would clog the system - and stop functioning as a conveyor belt. How too does it function for part of eternity - at least for billions of years?

 

Also the source(s) of this magma must itself be sufficient to provide hot cover for 196,940,400 square miles - and it has to let seismic waves pass through it - and it has to let the shock waves of earthquake pass through it.

 

gf

/

[D H]

I'm a new member ...

... and you're not off to a good start. Use of fallacies is strongly forbidden at this site. The title of the thread uses of scare quotes around physics, implying there is no physics in geophysics. So, fallacy #1, appeal to ridicule.

 

An article appeared on CNN.com not long ago that discusses the issue, stating ::

 

http://cnnwire.blogs.cnn.com/2009/08/25/u-s-students-fall-behind-international-counterparts-in-math-science-analysis-says/

 

Here (in part is why) :: One of the major tenets advanced by geophysics is that flowing magma propels the plates and causes oceanic plate separation at the mid-ocean ridges.

• Fallacy #2: Another appeal to ridicule, this one a lot more out in the open than the scare quotes in the title.
  
• Fallacy #3: Non sequitur. The cited article has nothing to do with geophysics.
  
• Fallacy #4: Red herring. This is a misrepresentation of plate tectonics.
  

 

 

But magma (by definition - being molten, fully expanded - having gone through phase change) has no means, in itself, to move an inch.

Fallacy #5: Composition fallacy. Magma is not partially molten and is not fully expanded.

 

Magma, by all definition, is a dead by-product of the heat that formed it.

Fallacy #6: Bare assertion. Just because you say something is so doesn't mean it is so.

 

 

I don't know what your hidden agenda is here. Don't keep it hidden: Why don't you just come out with it? How do you explain

1. The well-observed fact that there is a 60,000 mile long series of mid-oceanic ridges that girdle the globe.
   
2. The well-observed fact that plates are moving apart from one another along these mid-oceanic ridges.
   
3. The well-observed extrusion of magma at several sites along the mid-oceanic ridge.
   

[gentleman-farmer]

D H

I don't know what your hidden agenda is here. Don't keep it hidden: Why don't you just come out with it?

 

gf ) There is nothing hidden in my intent, or in the manner I phrased the subject line :: Examining the "physics" in geophysics. I intend to challenge the tenets

 

You may have made the task a bit easier :: by example you wrote

 

D H

How do you explain

1. The well-observed fact that there is a 60,000 mile long series of mid-oceanic ridges that girdle the globe.

2. The well-observed fact that plates are moving apart from one another along these mid-oceanic ridges.

3. The well-observed extrusion of magma at several sites along the mid-oceanic ridge.

 

gf) That is exactly the point :: "well-observed," "well-observed," "well-observed!"

 

Science is not about "well-observed!" It is about physical principles and the mathematical formulations that define and support those principles

 

Still I'll answer (in part) your three questions. But it can only be done (in part) because we have to set magma intrusions (as the driving force) aside and introduce a force that can be quantified. I intend to do that - but it's premature at this point

 

1.) My answer is that magma intrusions are incapable of exerting a lateral force.

 

2.) Magma has already gone through the only stage during which a force exists. That is the formation stage.

 

3.) When the ridge is open nothing prevents the intruding magma from just spilling harmlessly out on the ocean floor

 

4.) It is recognized by Cornell University (see noted 1) that magma does not open the ridge - the ridge must be open first - in order for magma to intrude (see quote below - the underlining is mine)

 

Although plate tectonics provides a general framework for understanding the distribution of volcanism over the earth's surface, many important aspects are poorly understood. Probably the best understood volcanism occurs at mid-ocean ridges. As the surface plates spread or diverge, hot mantle rock ascends to fill the gap."

/

/

Noted 1. SOURCE :: D. L. Turcotte, "MAGMA MIGRATION," Department of Geological Services, Cornell University, Ithaca, New York, 14853.

http://arjournals.annualreviews.org/doi/abs/10.1146%Fannurev.ea.10.050182.002145

[Sisyphus]

I was under the impression that magma moved through convection, not because it's melting.

[gentleman-farmer]

Sisyphus

I was under the impression that magma moved through convection, not because it's melting.

 

gf) Convection is the flow of heat - and cannot be related to the flow of magma. When there is a vast amount of heat - materials will boil (go to the gaseous stage) but that is very local - and in volcanoes would by pyroclastic

 

 

gf

/

[Mr Skeptic]

What keeps the magma molten is the heat generated by nuclear decay at the core of the earth. This heats the surrounding magma, which expands (almost everything expands when heated). Buoyancy then forces the hot magma to rise (this is how convection currents work). Since the magma is hotter than the surface of the earth, some amount of heat flow must exist from the magma to the surface (and then out to space). All this means that the magma, and convection currents in general, have the ability to do work. Feel free to experiment with this by heating a fluid on your stove and watching for movement.

[Sisyphus]

Convection is the flow of heat - and cannot be related to the flow of magma.

 

Convection is a flow of heat by means of a flow of matter.

[swansont]

D H

 

1.) My answer is that magma intrusions are incapable of exerting a lateral force.

 

2.) Magma has already gone through the only stage during which a force exists. That is the formation stage.

 

Is it under pressure?

[gentleman-farmer]

Mr Skeptic

What keeps the magma molten is the heat generated by nuclear decay at the core of the earth.

 

gf) That is precisely what's wrong with the physics in geophysics - the core is principly iron and couldn't support nuclear decay if it wanted to

 

Beyond that - there is no evidence of radioactive decay from any volcano, any lava flow, hot springs, or any other manifestation.

 

It is all say-so and exceeds even the realm of speculation

 

gf

[Mr Skeptic]

You do know that you are radioactive, right?

[swansont]

Beyond that - there is no evidence of radioactive decay from any volcano, any lava flow, hot springs, or any other manifestation.

 

Wow.

 

Bald assertion doesn't go over too well, and it's especially loathsome when it's blatantly wrong. We like evidence.

 

One of the ways you can find the age of a lava deposit is by radioactive dating (K-Ar), which wouldn't work so well if there were no radioactive materials in the lava.

[D H]

There is nothing hidden in my intent

I call bull. Or rather, I call crackpot. Everything you have posted here is screaming "crackpot". If you don't want to give that perception perhaps you should change your style.

 

Emphasis mine:

You may have made the task a bit easier :: by example you wrote

(See list at end of post #6)

 

That is exactly the point :: "well-observed," "well-observed," "well-observed!"

 

Science is not about "well-observed!"

Thanks for reminding me that science is not about observation.

 

A clue for you: Science is all about observation. It was observations, for example, that led to the development of the theory of evolution and quantum mechanics -- and of modern geology.

 

The observation of the mid-oceanic ridges, coupled with the observation of the increased age of the oceanic crustal rock with increased distance from the mid-ocean ridge, was the driving factor that led to the development of plate tectonics. Modern geology has explained those phenomena to a remarkable extent given that modern geology is only about 50 years old. The discovery of the mid-oceanic ridge marks the birth of modern geology.

 

 

Still I'll answer (in part) your three questions. But it can only be done (in part) because we have to set magma intrusions (as the driving force) aside and introduce a force that can be quantified. I intend to do that - but it's premature at this point

 

1.) My answer is that magma intrusions are incapable of exerting a lateral force.

Just because you say so doesn't mean that it is true. Prove it.

 

2.) Magma has already gone through the only stage during which a force exists. That is the formation stage.

Wrong. You are implicitly assuming that the magma melts completely and abruptly. That simply is not the case. The fraction of material in magma that is melted increases as the magma rises. Even erupting lava is not fully melted. You are also ignoring pressure and buoyancy here.

 

3.) When the ridge is open nothing prevents the intruding magma from just spilling harmlessly out on the ocean floor

Once again, just because you say so doesn't mean that it is true.

 

You haven't answered a thing. All you have offered are ill-formed opinions about the existing explanations. You have offered no explanations of your own. I'll challenge you once again: how do you explain:

• The well-observed fact that there is a 60,000 mile long series of mid-oceanic ridges that girdle the globe.
  
• The well-observed fact that plates are moving apart from one another along these mid-oceanic ridges.
  
• The well-observed extrusion of magma at several sites along the mid-oceanic ridge.
  
• The well-observed magnetic striping of the sea floor, with the stripes parallel to the the mid-oceanic ridges.

Do keep in mind that science is first and foremost about explaining observed phenomena.

 

4.) It is recognized by Cornell University (see noted 1) that magma does not open the ridge - the ridge must be open first - in order for magma to intrude (see quote below - the underlining is mine)

Although plate tectonics provides a general framework for understanding the distribution of volcanism over the earth's surface, many important aspects are poorly understood. Probably the best understood volcanism occurs at mid-ocean ridges.

As the surface plates spread or diverge, hot mantle rock ascends to fill the gap.

"

 

/

/

Noted 1. SOURCE :: D. L. Turcotte, "MAGMA MIGRATION," Department of Geological Services, Cornell University, Ithaca, New York, 14853.

http://arjournals.annualreviews.org/doi/abs/10.1146%Fannurev.ea.10.050182.002145

First off, your link doesn't work. Please check that your links work in the future. Secondly, if you had gotten the link correct it would have linked to a pay site. That's not nice.

 

Here is a link to the full article:

http://adsabs.harvard.edu/full/1982AREPS..10..397T

 

This article is 30 years old. Whether ridge-push and slab-pull is the dominant process at the mid-oceanic ridges was not known back then and remains an open question. Note well: Just because there are open questions in some science does not mean that the science is questionable. It just means that the science does not have all the answers -- yet. That's a good thing, not a bad thing. It means that work remains to be done, papers remain to be published. A science that has all the answers would be rather boring.

[gentleman-farmer]

Swansont

Wow. Bald assertion doesn't go over too well, and it's especially loathsome when it's blatantly wrong. We like evidence.

 

One of the ways you can find the age of a lava deposit is by radioactive dating (K-Ar), which wouldn't work so well if there were no radioactive materials in the lava.

 

gf) The Bald assertion was advanced by Mr Skeptic who stated that the heat within the earth originated at the core (which is primally iron) - if you are willing to support that assertion - I'd be glad to see it

 

That there are some small quantities of active material in lava - does not relate to Mr Skeptic's assertion

 

For your convenience I've copied a short description

Potassium–argon dating or K–Ar dating is a radiometric dating method used in geochronology and archeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites. In these materials, the decay product is able to escape the liquid (molten) rock, but starts to accumulate when the rock solidifies (recrystallises). Time since recrystallization is calculated by measuring the ratio of the amount of 40Ar accumulated to the amount of 40K remaining.

 

As you can see the process does not relate to active processes within the earth as proposed by Mr Skeptic

http://en.wikipedia.org/wiki/K%E2%80%93Ar_dating

 

gf

Edited July 8, 2010 by gentleman-farmer
adding detail

[Mr Skeptic]

Because heat loss relates to surface area, and heat generated by radioactivity relates to volume, and surface area increases as r^2 while volume increases as r^3, any amount of radioactivity (if sustained) will be enough to raise the temperature to any arbitrary temperature, simply by making the planet bigger. If you multiply the weight of the earth by even a tiny amount of radioactivity per mass you get a huge amount of radioactivity overall.

 

http://www.physorg.com/news62952904.html

Radioactivity is present not only in the mantle, but in the rocks of Earth's crust. For example, Marone explains, a 1-kilogram block of granite on the surface emanates a tiny but measurable amount of heat (about as much as a .000000001 watt light bulb) through radioactive decay.

 

That may not seem like much. But considering the vastness of the mantle, it adds up, Marone says.

 

There's also other things that can heat the Earth, such as tidal forces.

[swansont]

That there are some small quantities of active material in lava - does not relate to Mr Skeptic's assertion

 

 

a) it wasn't meant to address Mr Skeptic's "assertion," it was meant to address yours ("there is no evidence of radioactive decay from any volcano, any lava flow, hot springs, or any other manifestation.") None ≠ small amount

 

b) radioactivity in the earth's interior isn't an assertion. It's a well-established fact. In recent years they've even been able to detect neutrinos from the beta decays, which have been dubbed geoneutrinos (which I feel is unfortunate, but that's neither here nor there)

[gentleman-farmer]

Swansont

it wasn't meant to address Mr Skeptic's "assertion," it was meant to address yours ("there is no evidence of radioactive decay from any volcano, any lava flow, hot springs, or any other manifestation.")

 

gf) You formulated that quote out of context - when it is quoted in good order it reads quite differently ::

 

This is the proper order

 

Mr Skeptic

What keeps the magma molten is the heat generated by nuclear decay at the core of the earth.

 

gf

That is precisely what's wrong with the physics in geophysics - the core is principly iron and couldn't support nuclear decay if it wanted to

 

Beyond that - there is no evidence of radioactive decay from any volcano, any lava flow, hot springs, or any other manifestation.

 

It is all say-so and exceeds even the realm of speculation

 

gf) As you can see the reference to radioactive decay from volcanos and lava flows clearly relates to Mr Skeptic's heat generated by nuclear decay at the core of the earth.

 

If you want to support Mr Skeptic's assertions - I sure would like to see it

 

gf

/

[swansont]

Well, no, the context really doesn't matter here; since magma isn't formed in the core, there's no reason to expect it to contain materials formed in the core. It will, however, contain materials found in the interior, and does contain radioactive materials.

 

I'll leave it to Mr Skeptic to address whether "core" was being used in the technical sense or the colloquial sense of "interior" (though his subsequent post makes it pretty clear it was the latter)

[Moontanman]

Gentleman-farmer, you main problem here would appear to be your belief that there are absolutes, the core of the earth is mainly iron but not absolutely iron, there is reason to believe the core of the earth is not quite pure iron. It has impurities, many of them are heavier than iron and radioactive. Here are a few examples of some possibilities that do indeed account for the heat of the earth.

 

Some are less likely than others but the gist of the idea is that the core of the earth is indeed radioactive and emits enormous amounts of heat that cause mantle materials to rise and spread and this action drives plate tectonics with is a good thing for us because if not the earth would be quite dead both geologically and much less hospitable to life as we know it...

 

http://geology.about.com/od/wildgeotheories/a/nuclearcore.htm

 

http://www.spacedaily.com/news/earth-03k.html

 

http://en.wikipedia.org/wiki/Structure_of_the_Earth

 

http://berkeley.edu/news/media/releases/2003/12/10_heat.shtml

 

http://www.scientificamerican.com/article.cfm?id=why-is-the-earths-core-so

 

http://www.physorg.com/news62952904.html

 

The amount of knowledge that can be gleaned but searching google is amazing!

[gentleman-farmer]

According to the folk on this science forum - the core is a nuclear heat generator (or call it what you will) this heat (in turn) causes the magmas near the surface to maintain a semi-liquid state (or low viscus state) and this magma propels the surface tectonic plates (by a means uncertain)

 

Magmas (depending on composition, and according to Tulane University) range between 650 C (1202 F) & 1200 C (2192 F)

 

According to this science forum - the temperature gradient measures from the core to the near surface magmas. It follows (therefrom) that earthquake cannot be the result of brittle fracture and sliding faults as the temperature gradient (core to surface) forbids that scenario

 

Tulane University, on the other-hand says this about that ::

 

In order for magmas to form, some part of the Earth must get hot enough to melt the rocks present. Under normal conditions, the geothermal gradient, which is how the temperature in the Earth changes with depth or pressure, is not high enough to melt rocks, and thus with the exception of the outer core, most of the Earth is solid. Thus, magmas form only under special circumstances, and thus, volcanoes are only found on the Earth's surface in areas above where these special circumstances occur.

 

http://www.tulane.edu/~sanelson/geol204/volcan&magma.htm

 

gf

[pioneer]

One variable I don't hear being talked about is water. Water under the pressures and temperatures within the crust, is called hydrothermal and can dissolve most minerals found in the crust. Also, water will condense at higher temperatures, when subject to extreme pressure, and will expand up to 10% when it liquifies. It has the right stuff to lift and sink plates.

 

Here is the scenario, liquid water covers the majority of the surface of the earth and can be found flowing and/or pooling on and under the surface of the land. In some places, the water is nearly as thick (deep ocean water) as the thinnest crust.

 

As water is squeezed by gravity through cracks in the crust, toward the mantle, hydrothermal water forms and will follow the thermal gradient toward high temperature and will dissolve downward. This can be demonstrated in the lab and is the main way one creates hydrothermal crystals using gravity and passive convection. Water eats downward (hot allows more to dissolve) and precipitates upward (cool dumps the minerals) renewing the capacity of the hotter water to keep eating downward toward the higher temperature.

 

On the surface of the earth, the sun is evaporating water which enters the atmosphere to form clouds. This cools the surface water and increases the thermal gradient. Lightning reflects another form of gradient that increases due to the solar evaporation. The sun plays a role.

 

We also have thermal convection inside the earth due to various factors such as radioactive decay. This convection upward, causes the water to physically reverse the bulk hydrothermal path toward higher temperature. This forced convection cools the hydrothermal solutions, precipitates out molten material, with the water, condensing at high pressure, expanding by 10%. Much of the water will still follow the thermal gradient back to higher temperature leaving magna to lower energy by moving to the surface.

[swansont]

According to this science forum - the temperature gradient measures from the core to the near surface magmas. It follows (therefrom) that earthquake cannot be the result of brittle fracture and sliding faults as the temperature gradient (core to surface) forbids that scenario

 

By what twisted logic does that follow?