A science question

Don't get me wrong, I think it's awesome. In a horrible, horrible way. But if I can conceal my identity behind ancient cabinet art, who's to say but you what avitar to use? If the shirt was laced across the front, that impression would come through a little stronger. And probably not that hard to photoshop.

and back toward the topic, folk?

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I think that my science question was answered, Jar. The Universe is a fascinating place and to imagine that this dust speck of a planet that i am on is still so fascinating itself?! Still, my point of reference is not so much external as internal.Here is another question, however:
Have scientists ever dug deep enough to sample the mantle? In other words, can we ever probe beneath the crust? (of the Earth)

Not to date, but stay tuned.They tried with the Mohole, but that was a flop.I'm pretty sure that the deepest we've gone is 5.6 miles, in the KTB Borehole. In Germany, where that hole was drilled, the crust is about 25 miles thick (The Earth's Crust).

I replied: "Not to date, but stay tuned". I was just assuming that someday we'll do it. Well, someday seems to be coming. From A Sea Change in Ocean Drilling:

quote:

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IODP may even take another shot at penetrating the Mohorovicic discontinuity. With the lubricating drilling mud circulating through its riser, Chikyu should be able to reach 6 kilometers and into the upper mantle. Such a hole would help refine knowledge of the structure, composition, and physical properties of the oceanic crust.

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See also The Deep-Sea Drilling Vessel Chikyu report.

Yeah, I just went (ok 3 weeks ago) to the "Emerging Science Museum" in Tokyo (well... Odaiba), where they had an exhibit describing the plan. Really cool, brutal stuff.Ben
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Holmes,I think (I could be wrong) that all heat is IR, which is one form of EMR (light); therefore, heat is light and can be "lost to space" according to your criteria.A quick google seems to confirm my hazy notion about all heat being IR.AbE:
I'm not saying you're wrong about this...it's just that I've never heard that a vacuum is an insulator...where did you get that information from? Perhaps it is only an insulator of electricity?--TheLitThis message has been edited by TheLiteralist, 03-06-2005 05:57 AM

TheLit tries to remember how physics works...The problem would seem to work out like this:(Assumptions)

1. The earth, at some point in the past, was completely or nearly completely molten. (Something that I don't actually believe, btw).
2. The sun produces joules at a constant rate (on average)
3. The earth produces joules at a constant rate (on average)
4. The earth loses joules at a constant rate (on average)
5. Overall, the earth is losing heat energy faster than it gains it (I'm not too sure I believe this, but that would be the necessary assumption if you are starting with a molten earth and ending up with a solid earth, right?)

(Constants)S = Joules per second received from the sun
E = Joules per second generated by earth (whatever the process)
L = Joules per second lost to space from the earth
J_max = Maximum joules that could be contained by a completely molten earth
J_current = Joules contained by earth currently(Variables)t = time the earth has been cooling(The initial equation)J_max + (S t) + (E t) - (L t) = J_current
The initial energy of the molten earth plus the total energy ever recieved from the sun plus the total energy ever generated by the earth minus the total heat ever lost by the earth equals how much energy the earth has now.(Solve for t)J_max + t(S + E - L) = J_current
t (S + E - L) = (J_current - J_max)(The final equation)t = (J_current - J_max) / (S + E - L)
The time period required for the earth to go from a completely molten body to its present partially solid state equals the change in the earth's total energy from its molten to its current state divided by the overall rate by which energy is lost from (or gained by) the earth.S, E, L, and J_current can all be measured, can't they? I would think that J_max could be figured out to a close approximation. This would give the "worst-case scenario" or oldest age possible (starting from the time that the earth was molten)--given the assumptions are all true.It seems doable to me...though I certainly don't have the resources to get the numbers to replace the varibles. But I certainly could have made some stupid error...it's been a long time since I took level I physics.Just foolin' around...
--TheLitThis message has been edited by TheLiteralist, 03-06-2005 05:39 AMThis message has been edited by TheLiteralist, 03-06-2005 08:18 AM

There are two ways that heat can be transmitted:

1. Conductively. There must be a physical connection to conduct heat. Grab one end of a metal rod and hold the other end over a fire and in a little while the rod will be too hot to hold. Heat was conducted up the rod from the fire end to our end.
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   Since a vacuum is the absence of matter, heat conduction cannot take place through a vacuum, and therefore a vacuum is a perfect insulator.
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2. EMR (Electromagnetic Radiation - light and radio waves are examples). The most well known form that transmits heat is IR (Infrared Radiation), which is just a particular frequency of EMR. Matter is very responsive to IR - molecules of matter readily accept energy of EMR at this frequency and begin moving more energetically (heat is the rate of motion of molecules - in solids they merely vibrate in place). Matter is also a good transmitter of IR, as long as it isn't too cold. That's why infrared goggles work so well at night - the warmer an object (a person), the brighter it appears in infrared goggles.
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   Much of the electromagnetic spectrum passes right through matter with little effect. For example, AM radio waves weaken only slightly when passing through matter. Your house presents little obstacle to AM radio waves. Massive concrete structures like bridges are another matter, which is why AM radio stations fade out under bridges. FM radio, at a higher and more energetic frequency, is less susceptible to absorption by matter, but even FM fades out when you go through tunnels. Any electromagnetic radiation that is absorbed by matter becomes heat.
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   Microwave radiation represents a good compromise of energy, transmission and absorption that makes it very useful for cooking. Like IR it is absorbed by matter (not all matter - microwaves pass through plastic and paper with little effect, but not water and many types of glass which absorb them readily), but unlike IR it also passes through much of matter. The additional energy of microwaves enables a fair percentage of them to penetrate to the interior of food and heat it faster.
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   Naturally a vacuum presents no obstacle to EMR. Heat (actually, energy which only becomes heat when absorbed at the other end) can easily be transmitted across a vacuum using EMR.

Holme's Message 13 that you were responding to actually already has good answers in the two immediately following messages by Coragyps and JonF, Message 14 and Message 15. They pretty much said what I just said, only more briefly and clearly.So, the short answer to the issue of how the earth radiates heat into space is through EMR, probably mostly in the infrared.--Percy

It's been done, except it was done before the discovery of radioactivity. The equations were both more and less sophisticated than yours; yours don't include the rates at which energy is conducted/convected from the interior of the Earth to the surface, but the "E" term for the enregy generated in the Earth was left out. Both turn out to be very important in the calculation. The variation of thermal conductivity with depth is also important, and that's tough to measure. You might want to look back at Message 11 in this thread.It turns out that there's a scanned copy of the chapter from which I took message 11 on the Web, minus some tables: CHAPTER TWO, Age of the Earth by G. Brent Dalrymple. It includes a lot more than I did. The Inner Workings of the Earth may also be interesting.I doubt that anybody has the resoures to get the values needed for a highly accurate calculation.

<*cough*>convection<*cough*>

One should remember that not only did I mention that (in passing) within my post (unfortunately rather poorly), but in response to the replies I got which made this clearer I noted that there would be a question of the amount of loss IR would provide.That is it seemed to me we would have a net gain, rather than a net loss in our energy budget, which means the earth can't "cool" through this method even if it is a potential source for cooling in general.Though there was a citation mentioned it appeared more or less to back up my feeling. In any case it certainly did not show that we would have a net loss over time. I'd be interested in knowing if anyone has a good energy budget for the earth and its atmosphere.As a side note, on reading your description of ER it struck me as an interesting possibility if our increased use of radio transmissions would be adding anything to "global warming". Obviously not in the sense that CFCs can trap heat better, but that it actually adds energy to the atmosphere. Maybe not, but it was something that just ran through my mind while thinking of bridges absorbing the "heat" of FM radio transmissions.This message has been edited by holmes, 03-06-2005 11:16 AM

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

If you're really interested, G. Brent Dalrymple has an excellent account of the early attempts at establishing the age of the Earth and sun through thermodynamic analyses on pages 27-47 of his book The Age of the Earth. He concludes: In other words, it's sort of like predicting the weather. We understand the processes of weather very well, all the temperatures and air pressures and fronts and wind speeds and solar heating and so forth, but we can't measure everything and they interact in so complicated a fashion that we can only get a general idea of what's going to happen tomorrow. It's the same with the earth's thermodynamic behavior - we know all the factors involved, but there are so many factors and their interactions are so complicated and we can't measure everything, so while we know the earth is cooling, exact quantitative details aren't possible at this time.The early thermodynamic analyses relied upon making reasonable assumptions which nonetheless had such a wide range that one could get any answer for the age of the earth one wanted, from millions of years to billions of years (but not thousands of years). Lord Kelvin, the most prominent of those making age estimates based upon thermodynamics, argued for an age in the range of 20-100 million years, but this contradicted geological and evolutionary indications of a much greater age. The discovery of radioactivity as a source of heat showed that the greater ages predicted by geology and evolution were closer to the mark, and thermodynamic analysis became much less a viable possibility because of the addition of yet another not-well-understood (at that time) variable.You say that you don't believe the earth was ever completely molten, and that you don't believe the earth is losing heat faster than it gains it, but this is an inevitable conclusion from the data. The greater the depth the greater the temperature we measure. Naturally we can only dig so deep, but seismic analysis reveals much about deeper layers, and we know that below a certain depth the earth is molten right now. The temperature gradient of hot in the center to cool at the outside is what you get with a spherical body radiating heat into space. If we had a net acceptance of heat from space then the gradient would run in the opposite direction, with hot on the outside and cool in the center.--Percy

Oops! But physically moving a hot object to transmit heat seems so, well, primitive! --Percy

Note the link in Message 40.