Discovery of the Earth’s Inner, Inner Core

Article written: 10 Mar , 2008
Updated: 26 Dec , 2015

The traditional view of the Earth’s interior has the crust (where we live), the upper and inner mantle, the outer core, and the inner core; wrapped around each other like layers of an onion. But now textbooks will need to be revised. It turns out there’s an inner, inner core.

The core of Earth is known to have an inner core of solid iron about 2,400 km (1,500 miles). Wrapped around that is a fluid outer core that reaches 7,000 km across (4,300 miles). As the solid core rotates inside the fluid core, it generates the magnetic field that helps us navigate, and protects the planet from harmful radiation and the effects of the solar wind.

Geologists from the University of Illinois at Urbana-Chamaign have been probing the interior of the planet, trying to get a better sense of its structure. And that’s harder than it sounds. You can’t just look down through thousands of km of solid rock.

There were using the natural waves that pass through the Earth after earthquakes shake on the surface. The waves are bent and reflected as they pass through the various layers inside the planet.

The team was specifically studying how the waves were affected as they passed through the solid inner core and were surprised to see that it wasn’t a uniform sphere of iron.

Instead, the seismic waves clearly showed that there’s an additional layer at a diameter of 1,180 km (733 miles), which makes this less than half the diameter of the inner core.

This is the Earth’s inner, inner core.

So what is it? Here’s what the lead scientists, Xiaodong Song had to say:

“Our results suggest the outer inner core is composed of iron crystals of a single phase with different degrees of preferred alignment along Earth’s spin axis,” Sun said. “The inner inner core may be composed of a different phase of crystalline iron or have a different pattern of alignment.”

It’s still iron, just not in the same crystalline structure. Perhaps its time to give the layers new names, inner inner core doesn’t quite work for me.

Original Source: University of Illinois News Release

31 Responses

  1. Andrew says

    If there’s a different layer of iron, shouldn’t that be detectable in the Earth’s magnetic field?

  2. Andy C says

    > If there’s a different layer of iron, shouldn’t that be detectable in the Earth’s magnetic field?

    Andrew, although I’m far from being an expert on the subject, I think the answer to your question is ‘no’, because it is not the crystalline phase that determines iron’s magnetism, but the electronic spin of the atoms (they’re all aligned in magnetised iron).

  3. Improbus says

    Maybe they should call it “the Pit”. Like a peach pit.

  4. Paul Freedman says

    How about “inner core mantle” and “inner core centre”

  5. Phil Glover says

    Phil says;
    How about ” core blimey ”
    Iron core- inner or outer, Why is anything heavy at the centre, what’s the big attraction ?

  6. Graham says

    I’m not an expert on these things, but as the Earth’s core is well above the Curie temperature for iron, I think the magnetic field will be due to electric currents flowing through iron as a conductor rather than any feromagnetic properties.

  7. Simon says

    I reckon ‘sub inner core’ or ‘inner sub core’!

  8. alphonso richardson says

    I like the sound of ‘inner core centre’. How about sub-core, outer & central?

  9. SC says

    Hardcore / Softcore


  10. Ed says

    How about “innermost core” and “inner core layer”?

  11. Drlove says

    How about the chewy nuget center!

  12. Dan says

    Perhaps “crystalline core”?

  13. David Braun says

    I saw an article which suggested that the inner inner core consists of very heavy metals, including radioactive ones such as uranium which may contribute to the maintainence of the fluidity of the iron core.

  14. me says

    I’m for “innermost core”!

  15. astrojr1 says

    How about inner core, middle core, outer core. The inner core is not inner any more so why hang on to it. Pluto’s not a planet, Janet, etc.

  16. Jim (himself) says

    Could it be possible that the rotational speeds of these two separate cores be the genesis of our magnetosphere.? Is the boundry between core 1 and core 2 constant in relative rotational speeds? How do they relate in axial repositioning ? Do they alter when the polarity shifts.? Is there a difference in the radioactivity between core 1 and core 2?

  17. Bubba J. says

    Is it possible that we living on the surface a stellar remnant?

    I mean look at the major chemical constituents of the planet.

  18. Jim (himself) says

    Is it possible to create the material of core 1 or core 2 in a labority setting? Do they share the same polarity ? Can we assume that the two core construct is the basis for all planitary developement in our system? How much difference is there in the density between core 1 and core2?

  19. Josh M. says

    I suggest we call it “Where Taco Bell gets their taco meat from”

  20. Eugene Dusina, nuke physics says

    The inner core is “known to be iron”. How entertaining…

    Common sense says, IF the earth was EVER liquid, that at the center would be concentrated the heaviest elements.

    U238 with its few pct. of 235, and a few miles in diameter and at a pressure of about 10E16, would be expected to spontaneously fission, heat to tens of kilodegrees, sufficient to reduce density till fission became stable, and run for years. EARTH WOULD BE EXPECTED TO HAVE NATURAL NUCLEAR REACTOR AT ITS CENTER, as would all planets which went through a liquid phase in their creation.

    This would explain why the temp of the ground goes up ad infinitim as one drills deeper, would it not?

    Scientists have always been run by dogma, generated by the political ones at the top, and all facts which do not agree with that, are hidden away in dusty drawers never again to be looked at again lest one be drummed out of the professions.

  21. Eugene Dusina, nuke physics says

    Forgot to mention these un-explainable facts are called artifacts, such as a fine gold chain embedded in lump of coal, metallic balls of impossible ultra precision and hardness, in African mines, as well as walls of concrete block polished to mirror fine, and dozens of other artifacts, impossible to explain with earth scientific knowledge.

  22. Phil Glover says

    Phil says
    Ever seen a wobble ball flying through the air.
    That’s exactly like planets would behave if that heavy iron core was just a teeny little bit off centre, and guess what , not one of the members of the solar system behaves that way.

  23. Alfredo Amador says

    It’s nice to know, now we have something new within something old. However, until we have a real good physical way to see these layers, inner core and inner inner core will do just fine. To me, this variable is just a constant anyway!

  24. Raúl Caicedo Astudillo says

    What would happen if inner core were the coldest zone of the planet?

    1. It would be compound by solid oxygen (paramagnetic)
    2. Outer core would be liquid oxygen (paramagnetic)
    3. αo2 orthorhombic solid oxygen phase would be magnetic
    4. Inner core would be a huge bubble floating in the center of the outer core.
    5. Inner core would have an empty space >1326 km of diameter in its center.

    The Earth’s magnetic field is originated by a paramagnetic mass like the liquid oxygen and magnetic-paramagnetic like the solid oxygen. The αo2 orthorhombic solid oxygen phase located in the central zone is responsible of magnetizing the entirety nucleus. When the temperature is not as low as to reach in the αo2 solid oxygen phase the nucleus is magnetized only when it is under the influence of an external magnetic field, like the Sun’s magnetic field for example, because the whole mass is paramagnetic. Due to the Sun’s magnetic field have polarity reversals each eleven year, The Earth’s magnetic field also have polarity reversals in times of global heating.

    Due to the intensity of magnetism of a paramagnetic is inversely proportional to the absolute temperature and the intensity of the Earth magnetic field has decreased 10% in the last 100 year, means that the global heating is in process and a polarity reversal of the Earth magnetic field may occur soon.

    A summary of this new theory would be sent if required. E-mail: [email protected]

  25. morgan says

    why is the inner core solid iron when the outer core is melted iron?

  26. Smarty pants says


  27. Smarty pants says

    But it didn’t give me much info

  28. jhonny says

    i think you all are jugganot noobs

  29. jhonny says

    de de de de de you all stupi d hoe

  30. This inner core is solid because it is pure iron, while the outer core has other impurities that lower its melting point. Think of it like freezing a soda- the ice forms as pure ice, while the rest of the soda gets more syrupy. The main difference is that unlike ice, solid iron sinks instead of floating.

  31. Alex says

    I suspect that the pressures involved have something to do with this, as well as iron purity.

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