back to article Core-blimey! Riddle of Earth's mysterious center finally 'solved' by smarty seismologists

The Earth’s core is solid, according to a pair of geophysicists who claim to have solved an 80-year-old conundrum concerning the planet's center. The suggestion that our home world has a liquid outer core containing a smaller solid inner core was put forward by Danish seismologist Inge Lehmann in the 1930s. Scientists have …

  1. Hollerithevo Silver badge

    So it's...

    Solid and yet not hard? Fudge, then?

    1. Steve Knox

      Re: So it's...

      Hot fudge.

      Very, very hot fudge.

      1. J. Cook Silver badge

        Re: So it's...

        "Churches! Churches! Lead! Lead!

        A DUCK! " *gasps*

    2. Mark 85 Silver badge

      Re: So it's...

      I was thinking boiled potatoes.... but fudge would work also.

      1. Adrian 4 Silver badge

        Re: So it's...

        Gravy. With a yorkshire pud in the middle.

    3. Tom Paine Silver badge

      Re: So it's...

      Fudge is partially crystaline... Perhaps it behaves as glass is often claimed? Hmmm, not sure a fudge drop experiment would be a good way to find out, though

    4. bombastic bob Silver badge

      Re: So it's...

      'Soft' solid - it might be metal in its 'plastic' state, that is, just at the melting point but not really liquid. Under pressure it would behave as if it were solid, and yet be a bit more like melted glass or slime... as opposed to a 'truly liquid' form like molten iron poured into molds and whatnot.

      As for the earth needing the core to sustain the magnetic field... I fear the potential of this being politicized some day. Just sayin'. Never underestimate etc..

      1. drewzilla79

        Re: So it's...

        "I fear the potential of this being politicized some day."

        I'm a hard core-er and love freedom, but that liberal idiot over there is a soft core-er.

        A slippery slope indeed...

    5. OssianScotland Silver badge

      Re: So it's...

      Hot fudge sundae, which will be on a Tuesday

      (GNU JP)

      1. Gobhicks

        Re: So it's...

        Lucifer's Hammer ahoy!

  2. Denarius Silver badge

    out of curiosity

    why only iron/nickel in inner core in theory? Surely some real heavy elements, Tu, Ur and so on must have dribbled down ? if so would the core be a liquid cooled iron moderated fission reactor in part ? Hence some of the heat powering circulating currents in outer core and lower mantle ? The rest coming from more routine radioactive decay. Also an alloy may match the observed lack of rigidity. Have I missed something[s]

    1. Saruman the White

      Re: out of curiosity

      Yes they would have, however the bulk of the core (maybe > 90%) is made up from Fe and Ni. You tend to ignore trace elements in that situation.

      1. Tom 7 Silver badge

        Re: out of curiosity

        Ignoring trace elements is not a good idea - carbon steel is a completely different beast to iron and only has 2% carbon in it. Could easily account for the fudge!

        1. cray74

          Re: out of curiosity

          carbon steel is a completely different beast to iron and only has 2% carbon in it

          Nitpick: the vast and varied family of alloys known as "carbon steel" covers steels with 0.05 to 2.1% carbon. With more carbon they're called "cast iron" and below that they're just iron...or steel. Some steels (especially some of the stainless family) hate carbon and try to exclude it.

          More on topic: While the many other elements in the core are worth considering, it is hard to do so. Even for a fixed alloy composition, mechanical properties, magnetic properties, and even chemical properties will vary by temperature, pressure, and time, hence the T-T-T (Time-Temperature-Transformation) diagrams used in metallurgy for plotting heat treatments. You can get substantially different properties for an alloy held at high temperatures because of different crystal structures, different amounts of segregation of alloying elements, and other microstructural changes.

          The problem with estimating the impact of other elements on the core's properties is that a) the exact composition is unknown and variations smaller than 0.1% can be significant; b) the core sits at a combination of temperature and pressure way off the usual metallurgy charts; c) it's hard to even simulate the core's conditions for more than a fraction of a second in diamond anvils or nuclear explosions, which makes normal metallurgical tests** challenging; and d) there are probably regional variations in composition just like the crust and mantle, and there are certainly temperature and pressure variations across the core's radius.

          So it'd be hard to fault geologists for approximating the core as a big lump of nickel-iron. They do, on occasion, allow for the presence of uranium and potassium-40 to help estimate the radioactive heat budget of the core.

          **My lab's Instron tensile test rig has a small environmental chamber fit for -100C to +600C at one bar of pressure (air or clean, dry nitrogen). There might be error if its results were extrapolated to the core's conditions.

    2. Ken Hagan Gold badge

      Re: out of curiosity

      I'm guessing (so hopefully someone who knows will chip in) but as I understand it, a solid core would be slowly (as in, a billion years or so) crystalising out of the melt (the outer core) and so it is to be expected that it will show some selectivity in what atoms it permits in the emerging crystal structure.

      Alternatively, perhaps it is a mixture but it is so predominantly iron and nickel that geologists don't sweat the details. Hmm ... now I'm curious, too. (Trundles off to

      "Based on the relative prevalence of various chemical elements in the Solar System, the theory of planetary formation, and constraints imposed or implied by the chemistry of the rest of the Earth's volume, the inner core is believed to consist primarily of a nickel-iron alloy. Pure iron was found to be denser than the core by approximately 3%, implying the presence of light elements in the core (e.g. silicon, oxygen, sulfur) in addition to the probable presence of nickel.[11]

      Further, if the primordial and mostly fluid (still forming) earth contained any significant mass(es) of elements denser than iron and nickel, namely the white (appearance) precious metals (and a few others) except silver, specifically the siderophile elements, then these would necessarily have differentiated to the very center of the core into concentric nested spheres by planetary differentiation, with the most dense (and stable, i.e. platinum, iridium, and osmium, (etc.) in order of density) of these forming the innermost spheroid(s).[12] While unstable elements of such trans-iron/nickel density would have mostly decayed to iron/nickel/lead by the time the earth formed a discrete core.

      See also: Densities of the elements (data page)

      It then necessarily follows that all, or almost all, of these denser elements we have mined (or are even able to) at the surface (or near surface, or even at all "above" the core) have been delivered later as part of impact objects/masses.[13] "

    3. Anonymous Coward
      Anonymous Coward

      Re: out of curiosity

      Everything wants to be iron.

      1. Michael Wojcik Silver badge

        Re: out of curiosity

        Everything wants to be iron.

        It doesn't so much want to be iron, as it just eventually gives up and settles for being iron.

        Iron is what matter becomes when it runs out of ambition.

    4. Anonymous Coward
      Anonymous Coward

      Re: out of curiosity

      Fissionables distributed thruout the body of the early Earth provided enough heat to encourage the Earth to differentiate by density. As the iron and nickel began falling to the core it released its potential energy as heat, completely melting the planet.

      Fissionables too, fell to the core, but the core is a big place, so probably the very rare fissionable atoms would not achieve the density needed for enhanced reactions. Not sure about that tho. If it did happen, it would have been while the planet was still molten, simply making it more so. And relatively quickly the fission reactions would have depleted fissionables to the point where fission ceases.

    5. bombastic bob Silver badge

      Re: out of curiosity

      "would the core be a liquid cooled iron moderated fission reactor in part"

      Evidence of former 'natural reactors' does exist. It may be why the core is STILL molten.

      And yeah, iron/nickel have stable atomic masses near 56, which is at the top of the binding energy per nucleon curve. In short, all fission and all fusion [that is exothermic] heads towards end products of iron 56-ish and nickel 58-ish. Cobalt too, but for some reason, not so much of it in the core.

      So yeah earth's core is basically dead-star-stuff, with the highest binding energy per nucleon, basically the lowest potential energy with respect to fusion/fission reactions. By contrast, hydrogen has the least binding energy per nucleon, and the highest potential energy for a fusion reaction - like in the sun.

      Sciency wikipedia article HERE.

      also relevant, fissionable material would've all fissioned away by now, more or less, if it had a tendency to sink deep into the core and form a critical mass. which it probably did.

      1. igmac

        Re: out of curiosity

        Well, the core is not STILL molten as the article points out (if it ever was)

    6. igmac

      Re: out of curiosity

      More likely the result of accumulated frictional heating caused by earth tides (

  3. John Smith 19 Gold badge

    Solid, yet not very hard?

    Mini baby bells.

    1. I ain't Spartacus Gold badge

      Re: Solid, yet not very hard?

      If so, I wouldn't bite into it. The roof of your mouth would not thank you...

    2. Anonymous Coward
      Anonymous Coward

      Re: Solid, yet not very hard?

      Luckily, there's a pill for that now.

  4. Archtech Silver badge


    One hopes these very tiny waves do not turn out to be like Schiaparelli's canals on Mars.

  5. SVV Silver badge

    Seismic J-waves from the centre of the Earth

    Caused by all the dinosaurs that live there stomping around.

  6. Rol Silver badge

    Let's not forget..

    At the time of Earths formation it was spinning like a top, and thus the centripetal forces combined with the maelstrom of a churning and boiling liquid would have had such an impact as to counter gravity's effect on the heavier elements.

    Later some heavy elements would still be liquid or even a gas while other less dense elements and compounds were solidifying, meaning we still couldn't rely on gravity to grade elements into layers based on their density in a solid state.

    Hence our expectation to find the heaviest elements at the core of out planet is unfounded.

    1. vtcodger Silver badge

      Re: Let's not forget..

      Don't overlook the role of water which is an excellent solvent. Our surface deposits of iron for example are largely (there are exceptions) iron compounds precipitated from aqueous solutions. We don't know a lot about the inside of the Earth. The Kola superdeep borehole was an ongoing series of surprises. It's hard to generalize about whether circulation in the liquid mantle and outer core redistributes dense materials upward from the core and/or light materials down toward/into the core.

  7. aks Bronze badge

    I've always imagined the Earth's crust and plate tectonics like a very slowly moving pot of porridge. The "soft" core might be imagined as a soggy lump.

    1. jumpyjoe


      It's a long long time since I did Geology 101 but I don't recollect anything about J-waves in Seismology. P, S and Surface waves,yes,

      Aren't J-waves something to do with cardiology?

      1. Def Silver badge

        Re: J-waves?

        J is merely the notation given to a S wave in the inner core of the Earth.

  8. JimmyPage

    Bold claim ....

    "...without that geomagnetic field there would be no life on the Earth's surface."

    No life ? At all ?

    I'm betting that quote came from someone who isn't a scientist and who doesn't play one on TV.

    I'd have felt more comfortable with the more accurate (and wordy) "...the earths geomagnetic field has been shown to play a significant part in the development of life on Earth."

    We have no idea what would have happened (or not happened) if it wasn't there. If science teaches us nothing else, it's that life seems to occur wherever you look for it.

    1. Brewster's Angle Grinder Silver badge

      Re: Bold claim ....

      You can't write anything these days without a Martian taking offence.

    2. Monty Cantsin

      Re: Bold claim ....

      "If science teaches us nothing else, it's that life seems to occur wherever you look for it."

      Not quite. Science has taught is that life seems to occur wherever you look for it *on Earth*. Where there's a magnetosphere to protect it from cosmic nasties. It hasn't shown up (yet) anywhere else we've looked.

  9. Admiral Grace Hopper Silver badge
  10. Sam Adams the Dog

    Gone fission....

    @denarius I think the belief is still prevalent that the reason that the earth has not cooled down more than it in fact has since the birth of the solar system is that heat has indeed been generated by fission reactions deep within.

    1. Another User

      Re: Gone fission....

      Kelvin had calculated the age of the earth to be between 20 million and 100 million years. Radioactivity and its effects were unknown when Kelvin performed his analysis. The current age of the earth is 4.5 billion years. This age can be explained by having a fission reactor in the core.

      I don‘t understand why and when the fission should have stopped. After this we are in the range of 100 millions of years range of Kelvin‘s calculation before the core gets too cold.

      1. Anonymous Coward
        Anonymous Coward

        Re: Gone fission....

        Take the KT extinction event. If it did not only wipe out the dinosaurs 66 million years ago. Accidentally it also disrupted the fission processes... This would make some interesting science fiction.

      2. Brewster's Angle Grinder Silver badge

        Re: Gone fission....

        There's tidal heating of the core by the moon. I imagine that dwarfs the energy from radioactive decay.

        (It's no coincidence that all the small rocky planets with an internal dynamo are having their cores massaged by a larger neighbour. )

  11. STOP_FORTH Silver badge

    Maintenance of the geomagnetic field

    Is this work performed by geomagnetic field maintenance engineers? Are their hi-vis jackets heat-proof?

  12. Monty Cantsin

    "The understanding of the Earth's inner core has direct consequences for the generation and maintenance of the geomagnetic field, and without that geomagnetic field there would be no life on the Earth's surface."

    This sentence seems to suggest that without an understanding of the inner core, the generation and maintenance of the geomagnetic field is at imminent risk, as is all life on earth. Quite an onerous responsibility for these geophysicists.

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