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Thread: Roughly 50% of Earth's Internal Heat Generated by Radioactive Decay

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    Roughly 50% of Earth's Internal Heat Generated by Radioactive Decay

    Radioactive decay in the planet’s core produces no more than 24 TW of the total 44 TW heat generated in earth’s core. 20TW is being generated by another mechanism(s).

    http://newscenter.lbl.gov/news-relea...-geoneutrinos/

    http://www.nature.com/ngeo/journal/v.../ngeo1205.html
    Partial radiogenic heat model for Earth revealed by geoneutrino measurements

    The Earth has cooled since its formation, yet the decay of radiogenic isotopes, and in particular uranium, thorium and potassium, in the planet’s interior provides a continuing heat source. The current total heat flux from the Earth to space is 44.2±1.0 TW, but the relative contributions from residual primordial heat and radiogenic decay remain uncertain. However, radiogenic decay can be estimated from the flux of geoneutrinos, electrically neutral particles that are emitted during radioactive decay and can pass through the Earth virtually unaffected. Here we combine precise measurements of the geoneutrino flux from the Kamioka Liquid-Scintillator Antineutrino Detector, Japan, with existing measurements from the Borexino detector, Italy. We find that decay of uranium-238 and thorium-232 together contribute  TW to Earth’s heat flux. The neutrinos emitted from the decay of potassium-40 are below the limits of detection in our experiments, but are known to contribute 4 TW. Taken together, our observations indicate that heat from radioactive decay contributes about half of Earth’s total heat flux. We therefore conclude that Earth’s primordial heat supply has not yet been exhausted.

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    I'm having a hard time determining what the big news here is.
    I can see a refinement of modelling the Earth's heat budget, and I can see some advances in neutrino detection. Either way, I think it's a commendable accomplishment.

    But; I'm having trouble with the way the article is worded and all that comes to my mind is "didn't they find this out in the early 1900's which overturned Lord Kelvin's estimate of the age of the Earth?"

    In other words, what's different?

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    Quote Originally Posted by William View Post
    Radioactive decay in the planet’s core produces no more than 24 TW of the total 44 TW heat generated in earth’s core. 20TW is being generated by another mechanism(s).

    http://newscenter.lbl.gov/news-relea...-geoneutrinos/

    http://www.nature.com/ngeo/journal/v.../ngeo1205.html
    There's tidal energy, from both moon and sun also contributing to the heat.

    There is also crystallization advancing from the centre of the planet, giving out latent heat.

    But I think the authors conclusion is not new. It was decided some time back that a lot of the heat is primordial, and takes a lot longer to radiate to space than Kelvin originally calculated.

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    How much heat is generated by the enormous pressures?

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    Quote Originally Posted by ExplorerAtHeart View Post
    How much heat is generated by the enormous pressures?
    Well, zero, pressure itself does not liberate energy, changing pressure can.

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    Quote Originally Posted by William View Post
    Radioactive decay in the planet’s core produces no more than 24 TW of the total 44 TW heat generated in earth’s core.
    I haven't read the article but the quote says
    The current total heat flux from the Earth to space is 44.2±1.0 TW
    That extra 24TW is not just being generated in the earth's core--I seem to recall that most of it comes from the mantle, especially the crust.

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    Thanks, so would the pressure contribute to the containment of that energy? ie make it harder for it to come out.

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    Quote Originally Posted by ExplorerAtHeart View Post
    Thanks, so would the pressure contribute to the containment of that energy? ie make it harder for it to come out.
    Well, yes, because the pressure goes to density, and the density causes a long random walk for any EM radiation to escape. The same thing happens in the Sun wherein it takes thousands of years for the EM to make it to the surface but only about eight minutes to reach us.

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    Quote Originally Posted by jlhredshift View Post
    Well, yes, because the pressure goes to density, and the density causes a long random walk for any EM radiation to escape. The same thing happens in the Sun wherein it takes thousands of years for the EM to make it to the surface but only about eight minutes to reach us.
    The density of the sun's core is ten times the density of the earth's core, and it's a hundred times bigger. According to this webpage I just dredged up. Even if it made a difference of thousands of years, that's not very long, over the thermodynamic age of the earth, is it?

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    Quote Originally Posted by grapes View Post
    The density of the sun's core is ten times the density of the earth's core, and it's a hundred times bigger. According to this webpage I just dredged up. Even if it made a difference of thousands of years, that's not very long, over the thermodynamic age of the earth, is it?
    True, do we have an educated guess how long the average time is for the Earth?

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    I think most of it is just by convection. And conduction.

    One of the problems (Kelvin's problem) with the heat loss at the surface is that a great deal of it is coming from radioactivity close to the surface.

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    Quote Originally Posted by grapes View Post
    I think most of it is just by convection. And conduction.

    One of the problems (Kelvin's problem) with the heat loss at the surface is that a great deal of it is coming from radioactivity close to the surface.
    Isn't it very interesting, and for me, amazing, that the system is not at equilibrium, and because of that, it has facilitated our evolution and facilitates our existence. (IMHO)

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    Alot of that energy gets transferred into the crust and causes the plates to fracture and move.

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


    The earth is losing 44 TW of energy as heat (core is cooling.) The paper quoted above notes 50% of the energy lost is being produced by radioactive decay.

    Some other energy source is providing 22 TW of energy.

    Heat flow
    Heat flows constantly from its sources within the Earth to the surface. Total heat loss from the earth is 44.2 TW (4.42 × 1013 watts).[12] Mean heat flow is 65 mW/m2 over continental crust and 101 mW/m2 over oceanic crust.[12] This is approximately 1/10 watt/square meter on average, (about 1/10,000 of solar irradiation,) but is much more concentrated in areas where thermal energy is transported toward the crust by convection such as along mid-ocean ridges and mantle plumes.[13] The Earth's crust effectively acts as a thick insulating blanket which must be pierced by fluid conduits (of magma, water or other) in order to release the heat underneath. More of the heat in the Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is by conduction through the lithosphere, the majority of which occurs in the oceans due to the crust there being much thinner and younger than under the continents.[12][14]
    The energy generated by tidal forces is not significant.

    Energy released due to the latent heat of crystallization is a possible source however that requires a change in physics to explain the magnitude of the difference. Note the Wikipedia article linked to will need to be revised as it stated that 90% of the internal energy was due to radioactive decay which is not correct.

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    This paper is a review paper that discussions some of the issues. Plate tectonics requires a heat source to drive the engine.

    http://www.mantleplumes.org/WebDocum...eister2005.pdf

    There are multiple modeling paradoxes create if it is assumed the energy source is primordial.


    Models of Earth’s bulk composition based on CI chondritic meteorites provide an unrealistically low radioactive power of ~20 TW,
    whereas enstatite chondrites are sufficiently radioactive to supply the observed heat flux, contain enough iron metal to account
    for Earth’s huge core, and have the same oxygen isotopic ratios as the bulk Earth. We devise a method to obtain K/U/Th ratios
    for the Earth and other planetary bodies from their power, including secular delays, and use this to constrain Earth’s cooling rate.

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    Quote Originally Posted by William View Post
    The earth is losing 44 TW of energy as heat (core is cooling.) The paper quoted above notes 50% of the energy lost is being produced by radioactive decay.

    Some other energy source is providing 22 TW of energy.
    Your source says
    "We therefore conclude that Earth’s primordial heat supply has not yet been exhausted. "
    Isn't this just the gradual loss of the earth's initial endowment of thermal energy? The net cooling of the core, which you refer to? Why do we need to propose some mysterious unidentified mechanism?

    Tidal energy is easily calculated, I saw a formula for it the other day. I presume that, if significant, it had not been overlooked.

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    So presumably the Earth is losing mass as a result of this radioactive decay, but insignificant quantities. Can anybody quantify this for me? I'm getting my units muddled.

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    Quote Originally Posted by Ivan Viehoff View Post
    Why do we need to propose some mysterious unidentified mechanism?
    We do not.

    If I remember correctly it has been shown that even our Moon has not completely reached equilibrium. [Lunar geophysicist jump in here; or would it be selenologist.]

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    william, what exactly is it that you want to discuss here?
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    Quote Originally Posted by tusenfem View Post

    william, what exactly is it that you want to discuss here?
    Hi tusenfem.

    The discussion of the research is now complete.

    We await a new paper.

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    Grapes, you have mentioned several times the closeness to the surface of radioactivity. I think I understand why that may be, but is there a difference of level of radioactivity between the ultramafic seafloor magma and subduction generated melts?

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    The following is a succinct summary of what was found.

    http://newscenter.lbl.gov/news-relea...-geoneutrinos/

    What spreads the sea floors and moves the continents? What melts iron in the outer core and enables the Earth’s magnetic field? Heat. Geologists have used temperature measurements from more than 20,000 boreholes around the world to estimate that some 44 terawatts (44 trillion watts) of heat continually flow from Earth’s interior into space. Where does it come from?

    One thing that’s at least 97-percent certain is that radioactive decay supplies only about half the Earth’s heat. Other sources – primordial heat left over from the planet’s formation, and possibly others as well – must account for the rest.

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    I have been following the earth's heat flux discussions and research for sometime. The expensive and time consuming neutrino investigation was done as there is a puzzling fundamental question as to what is providing the source of the energy.

    The results of the neutrino investigation is:

    One thing that’s at least 97-percent certain is that radioactive decay supplies only about half the Earth’s heat. Other sources – primordial heat left over from the planet’s formation, and possibly others as well – must account for the rest.
    As noted in the below linked paper basic calculations indicate primordial heat is not the source. Other calculations rule out crystallization as the source.

    The paper linked to below tried to explain the additional heat source by increasing the amount of radioactive elements in the earth. The neutrino investigation provides direct observational evidence that constrains the amount of radioactive material in the planet.

    http://www.mantleplumes.org/WebDocum...eister2005.pdf

    Subsequent assessments of Earth’s surface heat flux require more heat than compositions based on the CI class can produce. The latest value for Qtot of 44 TW (Pollack et al., 1993) is 2.3 times QR provided by various CI models (compiled by Lodders and Fegley, 1998). To explain this difference, additional heat sources and processes have been proposed. Consensus does not exist, and the hypotheses fall into several classes: (i) delayed secular cooling, wherein the surface flux includes stored internal emissions from an earlier age that exceed the current amount generated (see discussions in Van den Berg and Yuen, 2002; Van den Berg et al., 2002), or (ii) high K content in the core (e.g. Breuer and Spohn, 1993), or (iii) remnants of primordal heat (QP) (e.g. Anderson, 1988a,b) delivered early in Earth’s history from impacts of accretion or decay of short-lived isotopes. Other possible heat releasing processes, such as crystallization of the inner core, contribute insignificantly (e.g. Stacey, 1969).

    Geological observations, inferred mantle overturn rates, estimated mantle cooling rates, and recent geodynamic models independently suggest that neither delayed secular cooling nor primordal heat are currently significant sources, necessitating that current heat production predominately originates in radioactive decay and is quasi-steady-state. Models of Earth’s bulk composition based on CI chondritic meteorites provide an unrealistically low radioactive power of ~20 TW, whereas enstatite chondrites are sufficiently radioactive to supply the observed heat flux, contain enough iron metal to account for Earth’s huge core, and have the same oxygen isotopic ratios as the bulk Earth. We devise a method to obtain K/U/Th ratios for the Earth and other planetary bodies from their power, including secular delays, and use this to constrain Earth’s cooling rate.

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    Is this leading to something?
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    Quote Originally Posted by captain swoop View Post
    Is this leading to something?
    Geological observations, inferred mantle overturn rates, estimated mantle cooling rates, and recent geodynamic models independently suggest that neither delayed secular cooling nor primordal heat are currently significant sources, necessitating that current heat production predominately originates in radioactive decay (my comment: Neutrino results indicates the heat source is only 50% due to radioactive decay) and is quasi-steady-state.

    We are awaiting the next paper on this subject. Perhaps there will be some new development that will resolve this puzzle.

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    Quote Originally Posted by William View Post
    We are awaiting the next paper on this subject. Perhaps there will be some new development that will resolve this puzzle.
    I'm not sure what angle the mods are coming from, but my angle was stated in my first post.

    We knew a portion of the heat is due to radiation, so what is new with this thread?

    As far as the other 50%... The paper doesn't address it, so there's nothing we can discuss about that as it relates to the paper.

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    Quote Originally Posted by William View Post
    We are awaiting the next paper on this subject. Perhaps there will be some new development that will resolve this puzzle.
    Then maybe next time when you start a thread, you might explain yourself a bit better and actually come up with the fact that you think there is a puzzle here?
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    Quote of a quote. Why do we need to propose some mysterious unidentified mechanism?
    We do not. Quote
    I suppose it is not good science to propose mysterious, unidentified mechanisms, but my guess is we cannot rule out mysterious unidentified mechanisms. Was William wrong in inferring that we should subtract the energy consumed by the plate tectonics from the energy radiated from Earth's surface? Do we know numbers for pressure changes, so we can subtract energy losses from energy gains? It seems erroneous to subtract 24 from 44 and conclude the whole 20 is from primordial heat. Worse all the numbers are subject to unreasonable doubt, if not reasonable doubt for some of them? Do we have a number for tide effect of the Moon and sun, or only that it is small compared to 44 terawatts?
    Apparently, we use equations to determine the percentage of thorium, uranium, potassium at each depth all the way to 4000 miles, yet we have possibly contaminated samples from a few thousand possibly atypical sites at depths of more than 2 miles. Worse we have likely tested rigorously less than half of the samples we do have from depths of more than two miles. Are we not being over confident when we suggest our numbers are + or - one terawatt? Neil

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    Quote Originally Posted by William View Post
    Quote Originally Posted by tusenfem View Post

    william, what exactly is it that you want to discuss here?
    Hi tusenfem.

    The discussion of the research is now complete.

    We await a new paper.
    Quote Originally Posted by William View Post
    We are awaiting the next paper on this subject. Perhaps there will be some new development that will resolve this puzzle.
    William,

    You were asked a question by a moderator, tusenfem, as to what you want to discuss, since your posts seem borderline for being non-mainstream. You give a somewhat cryptic answer that the discussion in now complete (which really doesn't answer the question), and then promptly proceed to post two more posts on a "complete" topic.

    When asked the question again, you give the same cryptic answer. Frankly, it seems like you are gaming the system and this behavior is borderline on trolling. This earns you an infraction.

    In future, do not play games. If you are just reporting some research, report it. If you are trying to make a point, then make that point clear.
    At night the stars put on a show for free (Carole King)

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    Interestingly, the wiki article on the earth heat references Turcotte and Schubert's 2002 edition of Geodynamics as saying the radiation component is 80%.
    Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%)
    Thanks to Jeffrey DreamKing at STatU for bringing this to my attention.

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