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Author Topic:   The great breadths of time.
gigahound
Inactive Member


Message 31 of 62 (314470)
05-22-2006 8:31 PM


Sorta moving on...
Ok, the math works...got it.
Now, how about rock that is actually in the ground? Such as the plutons that were mentioned earlier. From what I've read, most are poking out of the ground, but also lie deep in the earth. It makes sense to me (though I couldn't seem to find anything to substantiate my thought process) rock will cool more quickly above ground simply because of the elements: wind, rain, night-fall, winter...and they should cool more slowly in the earth because they are insulated, somewhat like a thermos.
Does Fink's law apply over the entirety of this formation? Or is there other math involved?
If the law does apply, how do the various levels of elemental cooling/deep insulation affect it (also, are there actual terms used for what I'm describing here?)

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gigahound
Inactive Member


Message 32 of 62 (314471)
05-22-2006 8:42 PM


Still on topic...mostly
Here is a link I found about some temperature readings taken from a cooling lava lake in a volcano; http://volcano.und.edu/...t/gen_hawaii_volcs/question13.html
In the diagram, is shows the lava solidifying above and below a hot melt...is this accurate? I would think that the lava chute beneath the volcano would still be melted as well...
http://hvo.wr.usgs.gov/volcanowatch/2003/03_01_09.html
Here, we see that the above lake has finally cyrstalized, which to me simply means that it has cooled considerably. It has taken approx. 43 years to reach this point and although no tests have been done since 1988 (at the time of the article) there is still consederable heat within the volcano. My question here is: is the heat a result of similiar insulating as normal rock would experience deep in the Earth, or might the volcano still be getting some energy from furthur below?

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gigahound
Inactive Member


Message 33 of 62 (314472)
05-22-2006 8:44 PM
Reply to: Message 32 by gigahound
05-22-2006 8:42 PM


Re: Still on topic...mostly
Also, can Fink's Law be applied here?
http://hvo.wr.usgs.gov/volcanowatch/2003/03_01_09.html
Here, we see that the above lake has finally cyrstalized, which to me simply means that it has cooled considerably. It has taken approx. 43 years to reach this point and although no tests have been done since 1988 (at the time of the article) there is still consederable heat within the volcano.

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JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 34 of 62 (314476)
05-22-2006 9:42 PM
Reply to: Message 31 by gigahound
05-22-2006 8:31 PM


Re: Sorta moving on...
they should cool more slowly in the earth because they are insulated, somewhat like a thermos.
Yup. "Insulation" is a reasonable term, but it's not the perfect term. They cool more slowly in the Earth because the temperature gradient is smaller; the rocks around them are hotter than the atmosphere or surface. A thermos works because it's a lousy conductor of heat; for a thermos, "K" in Ficks law is a small number.
Does Fink's law apply over the entirety of this formation? Or is there other math involved?
Fick's law. A slightly more complex version applies; in the version presented before "K" is a constant. That's only strictly true as long as we are considering only one material in one state. If significantly different materials are involved, there's a different value of "K" for each, and if some of the stuff is molten and some is solid and some is gas there's a different value of "K" for each. But for approximate calculations the original versionis acceptable.
In the diagram, is shows the lava solidifying above and below a hot melt...is this accurate? I would think that the lava chute beneath the volcano would still be melted as well...
I bet it's accurate. I'm not a field geologist, but I'm guessing that the "pipes" through which the lava erupted are fairly small diameter compared to the extent of the "lake". That would lead to a high temperature gradient (large difference in temperature between the center of the pipe and the walls, and a small distance from the center of the pipe to the walls; divide the former by the latter and you get a much bigger number than for the lake with its large distance). That would lead to high heat transfer, cooling the magma in the pipe until it solidifies. Until the pressure of the magma below breaks it and we get another eruption.
might the volcano still be getting some energy from furthur below?
It is; it's hotter below than it is above, heat flows from hot to cold, therefore heat is flowing. But it's almost certainly negligible, becasue the distance is quite large, leading to a smallish temperature gradient.
Also, can Fink's Law be applied here?
Fick's law. Yes, or perhaps the more complex version, depending on where you draw the boundaries of the system you are considering.

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gigahound
Inactive Member


Message 35 of 62 (314722)
05-23-2006 7:12 PM
Reply to: Message 34 by JonF
05-22-2006 9:42 PM


Re: Sorta moving on...
Thanks for all the clarification about FICK'S law!!
Now, is it true that when an object is hot, it begins cooling rapidly, and then slows down as it cools further? Is there a term for this?
If true, can Fick's law be modified to show the trend?

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gigahound
Inactive Member


Message 36 of 62 (314724)
05-23-2006 7:18 PM
Reply to: Message 8 by NosyNed
05-20-2006 10:57 AM


Re: Chemistry
You talked about cooling. That only applies to igneous rock. That starts in a moten state (think lava in hawaii).
The "universal" idea about rocks and minerals is that it takes Time, Heat, and Pressure for them to form. Time being the order of events required to pile on the pressure which creates the heat.
How far off am I here? Much of what I "know" is left over from grade school and snippets from hobby books.

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JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 37 of 62 (314733)
05-23-2006 8:02 PM
Reply to: Message 36 by gigahound
05-23-2006 7:18 PM


Re: Chemistry
The "universal" idea about rocks and minerals is that it takes Time, Heat, and Pressure for them to form. Time being the order of events required to pile on the pressure which creates the heat.
Different types of rocks require different amounts of time to form. Igneous rocks like basalt form pretty quickly.
The pressure and heat are found inside the Earth, but neither is caused by the other. The pressure is created by the weight of the rock above; the heat is created by radioactivity and some leftovers from the formation of the Earth. Rocks are "subducted" into the ground by the processes of plate tectonics, and there they encounter the heaat and pressure that turns them into metamorphic rocls. Then more plate tectonics processes return them to the surface or near the surface.
The 3 Types of Rocks
Discover How Rocks Are Formed!
Geology : Plate Tectonics

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gigahound
Inactive Member


Message 38 of 62 (314741)
05-23-2006 8:27 PM
Reply to: Message 37 by JonF
05-23-2006 8:02 PM


Re: Chemistry
So then, what we have are actually two heating processes, correct?
Plutons, which in general are mountains (at least, that's what I got from the reading I did.), are formed directly from molten mass.
Mineral layers are actually formed from the heat produced by decaying atoms.
Fick's law is great for tracking the cooling of molten masses, but I assume it cant be used on layered minerals (except under controled conditions?) because they would be physically cool (radioactive decay wouldn't happen fast enough to actually heat the mass would it?).

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MangyTiger
Member (Idle past 6353 days)
Posts: 989
From: Leicester, UK
Joined: 07-30-2004


Message 39 of 62 (314745)
05-23-2006 8:35 PM
Reply to: Message 35 by gigahound
05-23-2006 7:12 PM


Re: Sorta moving on...
Now, is it true that when an object is hot, it begins cooling rapidly, and then slows down as it cools further? Is there a term for this?
In general terms I think that is just Newton's law of cooling (scroll down to the bottom half of the page).

Never put off until tomorrow what you can put off until the day after

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JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 40 of 62 (314755)
05-23-2006 8:58 PM
Reply to: Message 38 by gigahound
05-23-2006 8:27 PM


Re: Chemistry
Well, there's really only one heating process; sometimes it's enough to melt the rock and sometimes it's not. When underground rock melts, the result is magma which can later turn into plutons, lava eruptions, or intrusions (which might be thought of as small plutons). When underground rock is heated and compressed significantly but not enough to melt it the result is metamorphic rock.
Plutons, which in general are mountains (at least, that's what I got from the reading I did.), are formed directly from molten mass.
They could be thought of as mountains, but they form and solidify completely underground, and are seldom called mountains. They sometimes become exposed by erosion of the surrounding material.
Mineral layers are actually formed from the heat produced by decaying atoms.
A "mineral" is a grain made up of one particular chemical composition and crystal structure. All rocks are made up of at least one mineral and are usually made up of many minerals. I think you mean "rock layers".
Magma (which is molten rock underground) is indeed melted by the heat due to radioactive decay of unstable atoms, although some of the heat is left over from the formation of the Earth. Metamorphic rock (underground rock which is heated and compressed enough to be changed significantly but is not heated enough to melt) is produced by the same heat plus the pressure of the rock above.
Fick's law is great for tracking the cooling of molten masses, but I assume it cant be used on layered minerals (except under controled conditions?) because they would be physically cool (radioactive decay wouldn't happen fast enough to actually heat the mass would it?).
Fick's law can be used for any situation in which something is diffusing between an area of high concentration and an area of low concentration. This includes heat transfer under any conditions. The math can get pretty complex when the shape of the thing you are interested in is complex and/or its composition varies significantly from place to place and/or what's going on at the boundary is complicated. But computers can do complex calculations very well.
Most of the heating of rocks is not from radioactive decay inside them; it's from heat transferred from the surrounding rocks, much of which heat originates ultimately in the deeper interior of the Earth. Earlier in the thread we saw that it takes a kilometer-sized pluton millions of years to cool ... well, it takes a long time for the originally-molten Earth to cool, plus heat is still being generated inside.
Geez, where are all the real geologists in this thread? This isn't my strongest suit, and this not a great medium for teaching basic geology ('cause doing diagrams is a PITA).
I suggest you look at my most-recently-posted links.

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 Message 38 by gigahound, posted 05-23-2006 8:27 PM gigahound has replied

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JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 41 of 62 (314756)
05-23-2006 9:00 PM
Reply to: Message 39 by MangyTiger
05-23-2006 8:35 PM


Re: Sorta moving on...
In general terms I think that is just Newton's law of cooling
Pretty general ... but Fick's law is more general, and Netwon's law of cooling is a special case of Ficks' law.

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gigahound
Inactive Member


Message 42 of 62 (314936)
05-24-2006 5:13 PM
Reply to: Message 40 by JonF
05-23-2006 8:58 PM


somewhat off-topic just to clarify
This site shows several images of what appears to be mountains, but are really batholiths, which if I understood correctly, are just really big plutons.
Plutons, which in general are mountains (at least, that's what I got from the reading I did.), are formed directly from molten mass.
They could be thought of as mountains, but they form and solidify completely underground, and are seldom called mountains. They sometimes become exposed by erosion of the surrounding material.
Edited by gigahound, : No reason given.

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gigahound
Inactive Member


Message 43 of 62 (314940)
05-24-2006 5:45 PM
Reply to: Message 40 by JonF
05-23-2006 8:58 PM


Re: Chemistry
You're right, I'm mixed up here about something, but that's ok, we're not really discussing minerals anyway.
However, I would like to have something clarified; Is the heat from just radioactive decay, or is it also from the deep? If so, then don't we have two heating processes?
Mineral layers are actually formed from the heat produced by decaying atoms.
A "mineral" is a grain made up of one particular chemical composition and crystal structure. All rocks are made up of at least one mineral and are usually made up of many minerals. I think you mean "rock layers".
Magma (which is molten rock underground) is indeed melted by the heat due to radioactive decay of unstable atoms, although some of the heat is left over from the formation of the Earth. Metamorphic rock (underground rock which is heated and compressed enough to be changed significantly but is not heated enough to melt) is produced by the same heat plus the pressure of the rock above.

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 44 of 62 (314942)
05-24-2006 6:02 PM
Reply to: Message 43 by gigahound
05-24-2006 5:45 PM


Heat sources
Is the heat from just radioactive decay, or is it also from the deep? If so, then don't we have two heating processes?
This is embarassing since I'm not sure I'm right but:
There is no heat "from the deep". If the earth had no radioactivity and had sufficient time to cool after the initial formation it would be the same temperature top to bottom.
Initially there was a great deal of non-radioactive heat from the kinetic energy of the masses that conglomerated into the earth in the fist place. Once there is nothing new (of significance) coming in that source stops. Though there may be a bit left after even all this time -- I dunno.
I'm guessing that most of the heat is now from radioactive decay.

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gigahound
Inactive Member


Message 45 of 62 (314943)
05-24-2006 6:04 PM


The story so far.
Creationists claim rock cools quickly.
Scientist say "NO!"
I asked "Why not?"
One solid proof for scientists is Fick's law which describes the rate of cooling of a mass. With some tweaking, this equation can determine the cooling rate for rock of varying size, varying rates of cooling, various depths...etc.
While this really isn't an answer to "Why not?", it does illustrate that cooling is not fast.
This might be enough to satisfy some people, but I guess I'm a bit more stubborn. For instance, it appears to me that while Fick's law shows the cooling process to be slow, isn't the process also hampered by the additional heat generated by continuing pressure, ongoing radioactive decay, and the rising of heat from the depths below?

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