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Nuclear Fission Confirmed as Source of More than Half of Earth’s Heat

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lavaNuclear fission powers the movement of Earth’s continents and crust, a consortium of physicists and other scientists is now reporting, confirming long-standing thinking on this topic. Using neutrino detectors in Japan and Italy—the Kamioka Liquid-Scintillator Antineutrino Detector (KamLAND) and the Borexino Detector—the scientists arrived at their conclusion by measuring the flow of the antithesis of these neutral particles as they emanate from our planet. Their results are detailed July 17 in Nature Geoscience. (Scientific American is part of the Nature Publishing Group.)

Neutrinos and antineutrinos, which travel through mass and space freely due to their lack of charge and other properties, are released by radioactive materials as they decay. And Earth is chock full of such radioactive elements—primarily uranium, thorium and potassium. Over the billions of years of Earth’s existence, the radioactive isotopes have been splitting, releasing energy as well as these antineutrinos—just like in a man-made nuclear reactor. That energy heats the surrounding rock and keeps the elemental forces of plate tectonics in motion. By measuring the antineutrino emissions, scientists can determine how much of Earth’s heat results from this radioactive decay.

How much heat? Roughly 20 terawatts of heat—or nearly twice as much energy as used by all of humanity at present—judging by the number of such antineutrino particles emanating from the planet, dubbed geoneutrinos by the scientists. Combined with the 4 terawatts from decaying potassium, it’s enough energy to move mountains, or at least cause the collisions that create them.

The precision of the new measurements made by the KamLAND team was made possible by an extended shutdown of the Kashiwazaki-Kariwa nuclear reactor in Japan, following an earthquake there back in 2007. Particles released by the nearby plant would otherwise mix with naturally released geoneutrinos and confuse measurements; the closure of the plant allowed the two to be distinguished. The detector hides from cosmic rays—broadly similar to the neutrinos and antineutrinos it is designed to register—under Mount Ikenoyama nearby. The detector itself is a 13-meter-diameter balloon of transparent film filled with a mix of special liquid hydrocarbons, itself suspended in a bath of mineral oil contained in a 18-meter-diameter stainless steel sphere, covered on the inside with detector tubes. All that to capture the telltale mark of some 90 geoneutrinos over the course of seven years of measurements.

The new measurements suggest radioactive decay provides more than half of Earth’s total heat, estimated at roughly 44 terawatts based on temperatures found at the bottom of deep boreholes into the planet’s crust. The rest is leftover from Earth’s formation or other causes yet unknown, according to the scientists involved. Some of that heat may have been trapped in Earth’s molten iron core since the planet’s formation, while the nuclear decay happens primarily in the crust and mantle. But with fission still pumping out so much heat, Earth is unlikely to cool—and thereby halt the collisions of continents—for hundreds of millions of years thanks to the long half-lives of some of these elements. And that means there’s a lot of geothermal energy—or natural nuclear energy—to be harvested.

Image: Courtesy of USGS





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  1. 1. CleverHans 6:54 pm 07/18/2011

    Nuclear decay is NOT generally considered "Nuclear Fission". The latter involves the splitting of a nucleus into 2 more or less equal parts (though additional less massive or massless particles may be emitted). The two parts are for the most part not exactly equal in mass, but tend to differ by several percent. But nuclear decay, which is warming the Earth, involves a slightly unstable nucleus emitting a much less massive particle, such as an electron or beta-plus particle (anti-electron or positron), an alpha-particle (helium nucleus) or, in rare cases a proton. Usually a gamma ray (photon) also is emitted, and the electron or positron is accompanied by a neutrino or anti-neutrino. Fission occurs on a timescale of a fraction of a microsecond, while alpha and beta decay can have timescales comparable to the age of the Earth, and thus still supply heat!

    Link to this
  2. 2. jtdwyer 7:24 pm 07/18/2011

    Exactly – radioactive decay is not nuclear fission, except in some cases that produce spontaneous fission in a very few rare, very heavy isotopes. Please see:
    http://en.wikipedia.org/wiki/Spontaneous_fission.

    The Science magazine News article reporting these research results makes no mention of fission. Please see:
    http://news.sciencemag.org/sciencenow/2011/07/earth-still-retains-much-of-its-.html

    Link to this
  3. 3. jtdwyer 7:30 pm 07/18/2011

    Also, please read "Lingering Lies: The Persistent Influence of Misinformation",
    http://www.scientificamerican.com/article.cfm?id=lingering-lies

    Link to this
  4. 4. Bryant H 11:24 pm 07/18/2011

    A shocking error in the title and story. Do you people actually read the articles you report on? Alpha decay is the major heat source not fission.

    Link to this
  5. 5. jtdwyer 11:30 pm 07/18/2011

    Does radioactive decay always produce a neutrino? The researchers seem to have used the number of neutrinos produced as a proxy for the heat produced by radioactive decay…

    Link to this
  6. 6. CleverHans 12:55 am 07/19/2011

    Alpha decay (emission of a helium nucleus) does not produce a neutrino. Beta decay does. Spontaneous fission (a rare process, as reported above by jtdwyer) generally does not but one of the fission products might then beta-decay.

    Link to this
  7. 7. calmasacow 11:09 am 07/19/2011

    Yes it very misleading but after the incident in Japan Nuclear fission gets peoples attention a lot more than Nuclear decay.

    Link to this
  8. 8. jtdwyer 12:48 pm 07/19/2011

    Thanks. I’m not knowledgeable enough to fully assess, but it seems that by focusing on neutrinos, these researchers’ accounting may have overlooked much of the heat being generated by radioactive decay that does not involve the emission of neutrinos.

    Link to this
  9. 9. doug123sa 2:09 pm 07/19/2011

    Well, to be kind the author obviously inadvertently conflated the terms decay and fission. The term fission appears twice in the body, in the same breath as decay. To the layperson (like me – ignorant but not stupid :) , it’s for the purposes of the article a subtle error. Nonetheless, they should fix it and someone ought to bring it more directly to their attention. I predict it is hard to change the headline, considering it’s already been published and indexed as part of the URL.

    The substance of the article is interesting. Unfortunately I can’t read the original w/o subscription, I hate that. The supplement briefly describes neutrino production.

    Link to this
  10. 10. smiler03 5:47 pm 07/19/2011

    If you click on the Nature Geoscience link in the first paragraph you will see where the theory emanated. There is absolutely no mention of fission in the originating article, it refers to "decay of radiogenic isotopes". I suggest the Author of this article desists from making things up in future.

    http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1205.html?WT.mc_id=TWT_NatureGeosci

    Link to this
  11. 11. CleverHans 11:16 pm 07/19/2011

    "Bryant H" has the best analysis. I finally remembered that the beta-decays are usually rather fast compared to the alpha-decays (emission of a Helium-4 nucleus). There’s a lot of interesting physics in why that is so slow- it is a matter of "barrier penetration." The alpha particle (containing 2 protons and 2 neutrons) has to pass through a classically impenetrable region or "barrier" around the surface of the decaying nucleus, where, if it were a classical (point or hard ball) particle it would be turned back, into the nucleus which is "trying" to decay. By "trying" I mean that in the end, net energy is liberated. The reason that the classical barrier is penetrated is that the alpha-particle’s wave function has a spread to it; in Quantum Mechanics particles are represented by waves and cannot be regarded as point-particles. They have a spread to them. The fact that the tail of the wave function tapers down rather fast means that many tries are needed before the alpha particle is emitted. It is all statistical; you can’t say "how many" tries or on which try the particle manages finally to exit. You can cook up a distribution of times for "trying" to exit and the mean of that distribution determines the decay rate, which can be a few per hundred million or even billion years. (U.S. billion = 10^9, not British billion which is 10^12). It is fascinating physics and I suspect it is even in George Gamow’s 1947 book: "One, Two, Three, Infinity"

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  12. 12. nfiertel 12:38 am 07/20/2011

    It would seem to me that thorium and uranium would sink to the iron core and be a part of the deepest and hottest part of the planet and not in the crust except in small amounts and thus the energy gained from its decay would be in depth whilst the potassium would be in the crust and the unstable isotopes of that would generate heat during its decay. more heat ought to be produced from the potassium decay than that of the heavier elements in the crust but I suggest that the heat generated by that which is deep within would remain longest in the earth and not dissipate by infrared emissions but would remain trapped and there would also be a lot more of it. The article is using an incorrect terminology. Unstable elements release particles and drop to lower proton numbered elements and this is NOT called fission which is a more energetic process and requires particular situations to occur naturally. There have been areas in the crust wherein fission have occurred resulting in strong evidence of this process but it is rare.

    Link to this
  13. 13. CleverHans 1:11 am 07/20/2011

    The separation of elements within the Earth over geologic time spans is not a simple diffusive settling due to differing atomic (or molecular) weights. There are two main classes of elements: "siderophile" or "iron-lovng" and "lithophile or "chalcophile" – broadly "rock-loving," though the two latter classes are a bit different. See: http://en.wikipedia.org/wiki/Goldschmidt_classification
    The elements most soluble in iron largely dissolve in iron and sink to the core when core formation happens. The chalcophile and lithophile elements bind into rocks in the mantle and crust.
    Diffusive settling would be far too slow – diffusion within rock or magma is at a tiny pace. The actual separation has to do with iron (or iron-nickel) globules forming and growing by coalescence, I believe. The larger globules can migrate through the molten or at least plastic rock and descend to the core. Much of the iron we mine may be not original iron, but may have been deposited in the bombardment of the Earth by meteorites (or even mini-asteroids) after core separation happened. See: http://news.nationalgeographic.com/news/2002/07/0725_020725_meteor.html
    for example. The bombardment time estimates tend to be about 3.7 billion years ago, while the core separation was perhaps 50 to 100 million years after the Earth’s origin 4.54 billion years ago. A lot of isotopic evidence goes into all this – in particular Hafnium vs Tungsten isotopes. Hafnium gets trapped in rocks, while Tungsten is siderophilic and thus easily trapped in iron, which will descend to the core unless it was late-arriving.

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  14. 14. dburjorjee 6:01 pm 07/20/2011

    Most disappointing article. Seems to confuse fission with decay, neutrinos with anti-neutrinos. The magazine deteriorates daily. Just compare with any artice published in the 1960s and 1970s. dont know why I don’t cancel my subscription.

    Link to this
  15. 15. JohnTalbutt 6:19 pm 07/20/2011

    Does anyone else find the use of the word "antithesis" to describe antineutrinos inappropriate?

    Link to this
  16. 16. sofistek 7:18 pm 07/20/2011

    "And that means there’s a lot of geothermal energy–or natural nuclear energy–to be harvested."

    Sigh. Even those who appear to be environmentally aware still fall into the trap of thinking us humans should harness whatever resource we can find. I don’t know if such harnessing would have detrimental impacts but I do know that, in nature, you can’t do just one thing. However, the point is also that this is a finite planet. We need to simplify our lives to give us a chance of not precipitating the extinction of our own species, just as we are bringing about the extinction of other species, at a rate that is two or three orders of magnitude more than the background rate.

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  17. 17. Keller 8:01 pm 07/20/2011

    When a heavy atom such as uranium splits, the fragments decay into other forms through various mechanisms and that generates heat. That decay process occurs over long time periods, as does and the dissipation of heat. In any case, the process starts with fission.

    Looks to me like fission is a naturally occuring process, just like "green" energy. Come to think of it, solar energy starts with nuclear energy.

    Link to this
  18. 18. CleverHans 12:37 am 07/21/2011

    In principle, fission of U-235 could happen but the decay is actually by emission of an alpha particle (Helium nucleus), resulting in Thorium 231.
    see

    http://www.ead.anl.gov/pub/doc/natural-decay-series.pdf

    To fission, the U-235 needs to absorb a neutron, but free neutrons within the Earth are essentially nonexistent. Very few decays or naturally present elements produce neutrons, and any produced are likely to be absorbed in some other more abundant element than Uranium. Boron-10, cadmium, phosphorus, silicon, and aluminum are much, much more abundant than Uranium and would soak up any free neutrons. See

    http://environmentalchemistry.com/yogi/periodic/crosssection.html

    As I said before, most of the long-term decays are due to alpha emission, although I forgot Potassium-40, which beta-decays with a long lifetime. It is a significant contributor to earth heating (but, once again, there is no fission involved).

    Link to this
  19. 19. Quinn the Eskimo 1:13 am 07/21/2011

    Half the world’s heat! From natural processes?

    Kinda kicks AGW in the ass, now don’t it? Or, is GM building nuclear powered cars now?

    There you have it! 50% of the heat — NATURAL.

    Link to this
  20. 20. jtdwyer 2:35 am 07/21/2011

    If I follow you well enough then, many if not most decay events produce heat but do not produce neutrinos – is this correct?

    If this is so, the researchers use of neutrino detections to apportion the Earth’s measured internal heating is seriously flawed – correct?

    Thanks for your very informative insights!

    Link to this
  21. 21. Jan Jitso 5:32 am 07/21/2011

    In 2003 there was presented a new theory on gravitation with as basic hypothesis that mass reduces the Heisenberg uncertainty. The author Vasily Yanchilin explains in his book The Quantum Theory of Gravitation (available for less than twenty euros with excellent mathematical work out following the principle of least action) that gravitation is a purely quantummechanical process. As I cannot reproduce his drawing illustration here I’ll say it thus: Imagine a mass at x=0 and a tiny particle at x=10. A next moment this particle may be at x=9 due to the Heisenberg uncertainty. Because at this point nearer to the external mass there is less uncertainty there will be less transitions back from x=9 tom x=10. The result is moving towards the mass, which in common language is called gravitational attraction. Note that quantummechanics is from later date than the general theory of relativity and Einstein himself took constancy of the speed of light a century ago, when first planes flew, only as a temporary hypothesis. He could not imagine that c was totally independent from everything else in the universe. Read the words electro-magnwetic waves, which indicate already some connection!
    So in the past the speed of light was bigger according Yanchilin and likwise bindings within the atoms. (See the book for argumentation). This means that inside Earth there was less radio-active decay in the past than at present. It also implies that the radius of our planet increases, which perhaps enables more radiation outwards also when varying materials get to the surface. So fine tuning according the new theory should follow.

    Link to this
  22. 22. CleverHans 10:31 am 07/21/2011

    Sorry – I had forgotten the Potassium 40, which does contribute to the heat and does produce neutrinos.

    The neutrino work is important because the alpha-particle decays are hrd to count up – the alpha particles (Helium nuclei) do not go far. But the daughter products may further decay with emission of electrons (beta-minus or even beta-plus [positrons]) and there’s always a neutrino emitted in beta-decay. For example, U-238 goes to Thorium-234, which beta-decays with a half-life of about 24 days. See:
    http://en.wikipedia.org/wiki/Uranium-238#Radioactivity_and_decay
    The decay of the Thorium to Protoactinium produces a beta-particle whose neutrino is too weak for Kamland or Borexino to detect, but almost at once most of the Protoactinium goes to another Uranium isotope with the emission of a more energetic beta-minus particle and a neutrino. See the same link as above. It is all very complicated but, basically, the scientists with the new information on Earth heat sources use the neutrinos, which travel very far, as signals of some of the decays that may have started their chains of decay with U-238, U-235, or Thorium alpha-decay, or even some neutrinos from Potassium-40.
    The researchers recently reported are very capable and use the emission of neutrinos in the well-known decay chains (one decay can lead to many, later, but usually not much later – seconds, minutes, or hours) to trace the original decays, most of which do not, as you say, produce neutrinos! It is complicated detective work, but well done.

    Link to this
  23. 23. Keller 11:03 am 07/21/2011

    The decay of fission fragments occurs over the space of thousands of years. That decay process generates heat. The dissipation of heat from the earth’s core takes a long time.

    Point of fact, the fission process is likely the source of the heat discussed in the article. Further, nuclear energy is the source of all green energy.

    Link to this
  24. 24. CleverHans 11:06 am 07/21/2011

    The production of internal heat from radioactive decay and the leakage of primordial heat by diffusion upwards in the Earth have been well-known long before the human-generated atmospheric (and oceanic) global warming was analyzed. Unfortunately, the best analyst of the latter, Steve Schneider, died about a year ago at age only 65, on a plane about to land in London. see:
    http://www.paloaltoonline.com/news/show_story.php?id=17609
    Most of the attacks on the concept or fact of global warming by atmospheric CO2 are done by politically motivated persons with financial interests in the burning of fossil fuel, or who are invested in or funded by such extraction and burning of fossil fuel. Our government is not supporting the reduction of CO2 emissions seriously enough (with tax credits or the like) . See: http://www.electricitypolicy.com/news/3343-aep-drops-carbon-capture-plant,-citing-uncertain-energy-policy
    This is a very sad turn. You can’t (I suppose) expect AEP to eat all the costs. So they are giving up. We in the U.S. will pay with heat-related illnesses, Yellow Fever and Malaria creeping north, and so on but the people in Bangladesh will die by the millions. Indonesia has some areas that will flood, but they are a sizable contributor to greenhouse gases, as well. See:
    http://www.american.edu/cas/economics/ejournal/upload/Global_Majority_e_Journal_1-1_Measey.pdf

    Dear dear – so many studies but so little progress. Unfortunately, if the changes go too far, ocean circulation may change for the worse. Maybe we can all go to Congress and sing songs about the "Titanic" – "It was Sad When the Great Ship Went Down." There is a version at:
    http://www.songlyrics.com/girl-scout-songs/titanic-song-lyrics/
    with some misspellings ("trough" for "through", "peir" for "pier" , "went the great ship went down", for "when the great ship went down".) Dear Dear, girls, practice spelling as well as singing. (Smiley-face omitted here)

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  25. 25. CleverHans 12:13 pm 07/21/2011

    nonsense (new relativity theories are a dime a dozen and not worth that – so far)
    See reviews by Clifford Will

    http://relativity.livingreviews.org/Articles/lrr-2006-3/
    and others such as Martin Bojowald

    http://relativity.livingreviews.org/Articles/lrr-2008-4/

    in
    http://relativity.livingreviews.org/

    These guys do not miss anything important and they do not mention Vasily Yanchilin. Tut Tut – keep up with the Living Reviews and you have access to the best minds.

    Link to this
  26. 26. CleverHans 12:16 pm 07/21/2011

    Item 28 was intended to be a reply to item 21 –
    Jan Jitso
    05:32 AM 7/21/11
    but evidently the click failed
    This is quite off-topic for Earth heating but I felt I had do do my best to quash patent nonsense.

    Link to this
  27. 27. robertwyattdavis 2:03 pm 07/21/2011

    I remember reading some time ago about a uranium deposit (in I think Russia the USSR at the time) that had depleted U235 and byproduct elements showing that a naturally occurring chain reaction had at one time taken place. When I saw the headline for this story I assumed that they had discovered more of this was happening deep in the earth’s mantle. Perhaps (I thought) they have discovered natural reactors are powering some of the geothermal hot spots like under the Hawaiian Islands. Sadly, no case was made for a natural chain reaction. I did note however that quantitatively only half of the energy source had been explained so maybe active natural reactors might still be discovered in places where the radioactive heavy elements are concentrated. A chain reaction would produce neutrinos and perhaps be detectable.

    Link to this
  28. 28. CleverHans 6:22 pm 07/21/2011

    You are right – there is evidence for a U-235 chain reaction "2000 million" (US 2 billion) years ago, in what is now Gabon (not USSR I guess) . see:
    http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor
    and, for the exact time-frame, see
    http://oklo.curtin.edu.au/when.cfm
    as well as the parent link. Since it’s an Australian link they are careful not to use "billion" which is a million million in most British Commonwealth countries, but is a thousand million here.
    Anyway it is an interesting story I did not know, so many thanks.
    I had said that there aren’t enough neutrons in the Earth to cause fission of U-235 but I had failed to point out (see the article) that you need slow neutrons, so you need a (water) "moderator".
    About "natural hot spots" powering heat under the Hawaiian Islands – I have no idea but the other articles say there is not enough U-235 left for fission such as happened at Gabon. Odd to see so much interest in fission, given that there has been relatively little attention to President Obama’s success with a treaty to reduce nuclear weapon stockpiles. The Republicans are trying to take away funding for the process of getting rid of the excess weapons. If they succeed they will ostensibly embarrass the President and at the same time cut off their noses to spite their faces, one might say.

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  29. 29. CleverHans 6:33 pm 07/21/2011

    In reply to myself (for all to see) I have a correction to

    http://oklo.curtin.edu.au/who.cfm

    It says: During the late 1950′s and early 1960′s, the 235U/235U ratio in hundreds of U ores from around the world were measured to detect any change in this ratio. Any reduction in this ratio would indicated that some 235U had fissioned some time in the past. Of the hundreds of ores investigated, none had a 235U/235U ratio outside the generally accepted value of 0.007202 +/- 0.00006
    Note that in the Web version the numbers 235 are superscripts. That’s actually the correct notation; nowadays the symbols U-235 or U-238 are wrong, but I can’t seem to enter superscripts here. Note also that the superscript precedes the element symbol (U).
    But there are clearly a couple of typos! The author means 235U/238U and not 235U/235U !! Glad he is not making bombs or medicines – you can kill people with typos. A couple of decades ago I saw that a nurse gave a patient Barium Sulfite to swallow before a stomach X-ray, instead of Barium Sulphate. The Sulfite (or Sulphite) is water soluble and poisonous. The patient died. The Sulphate is virtually insoluble and can be used as an X-ray contrast medium.

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  30. 30. Dr. Strangelove 9:24 pm 07/21/2011

    That nuclear energy is the source of earth’s internal heat has been known or speculated on since the discovery of radioactivity in 1896. Lord Kelvin calculated in the 19th century that a molten earth would cool in about 100 million yrs. But geologists at that time knew that earth was billions of yrs old. So they theorized that the heat must also be coming from radioactivity. 110 yrs later it is confirmed. If not for nuclear energy, there wouldn’t be geothermal energy today.

    Link to this
  31. 31. jeff.shaw 7:37 pm 07/23/2011

    I believe other potential sources of geothermal energy have been proposed. One that seems rational to me is friction due to tidal distortion of the earth. I know from personal experience that groundwater levels in wells located in the middle of the continent experience tidal fluctuations of a couple of centimeters or so. The water is mobile, thus it responds to tidal forces in the aquifer (as expressed in the well) like the ocean, but the response is attenuated by the energy required to overcome the aquifers’ resistance to flow.

    It seems to me that the rocks, like the fluid, also must distort twice per day on a microscale, at the level of small fractures, and intergranular or intercrystalline contacts. All these points of movement (and frictional heat) could add up to a significant total in the millions of cubic miles of rock in the crust and mantle. The mantle is plastic, so the heat generated by distorting it twice a day wouldn’t be through fractures but through friction between crystalline grains. Anyway, I first heard this hypothesis as an undergrad and it seemed intuitive and rational to me. Perhaps it accounts for at least part of the other half of geothermal heat.

    Link to this
  32. 32. Bengtj 1:57 pm 07/27/2011

    How can you compare a unit of power measured in TW (20 TW of heat) with energy "as used by all of humanity at present".
    Energy = Power x time

    Bengt Johansson

    Link to this

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