The article kind of glosses over a key point about how all of this works and why "rotation" vs "shape changing" are difficult to distinguish. That's all because of anisotropy of seismic velocity in the inner core.
In other words, sound (seismic waves) travels much faster in one direction than the other through the inner core. That's true of most rocks to some degree, and it implies that the crystalline iron in the inner core is mostly aligned in a similar direction. But that is at the core (pun intended) of all of this.
So the "fast direction" has subtly changed over time based on the data we have. That's the "the Earth's inner core rotates differently than the rest" part. But we're mostly basing that on travel times in each direction (it's more complex than that - more in a bit). The differences "more fast stuff" and "less slower stuff" are hard to distinguish precisely, though they can be distinguished because of effects that occur at the boundary between different velocity + density bodies. It's also harder because the outer core is liquid and removes a key source of information coming from wave interactions at those boundaries (shear waves).
This is basically doing a lot of clever reprocessing of old data to carefully look data after corrections for the moderately-well-constrained rotation of the inner core. Rotation of the inner core can't explain all of the differences, so another thing that might cause it is changes in the shape of the boundary between the inner and outer core. It's also possible it's noise, though presumably the authors investigated that part carefully (haven't read the scientific article, but the primary author is a very well known person in the field, so the analysis is likely very sound).
There are always alternate explanations, though. Changes in shape on the order called for here do need an explanation via geological processes. Kilometer scale changes in a decade are difficult to immediately explain, though not impossible. I have no doubt the analysis is sound, but from a geologic perspective, this (and previous) work raises a lot of interesting questions.
Additionally, the magnetic shape and location of the poles are also shifting, which I think suggests the core is also shape changing.
jofer 17 hours ago [-]
In this case, it's not directly related. The inner core isn't what causes the Earth's magnetic field. It's convection within the liquid outer core that gives us a strong magnetic field. The inner core changing shape wouldn't necessarily cause changes in the Earth's magnetic field.
admissionsguy 1 days ago [-]
That's a great headline. Maybe not for a non-fiction article, but a great headline nonetheless.
xg15 1 days ago [-]
Yeah, gotta admit, had to think of Lovecraft for a second.
Would also fit the weird events in Italy's Campi Flegrei and Greece's Santorini island recently.
No, I'm not serious :)
knighthack 1 days ago [-]
The underground lizard people doing their thing, of course.
amelius 1 days ago [-]
If you like that headline, you will love this movie:
The headline only needs one minor twist also to give some political entities a reason to blame climate change on something other than the burning of fossil fuels.
A title like: we can detect forces inside the Earth that deform it, even though the Earth overall is smoother than a ball bearing, just wouldn't get enough clicks.
Interesting choice of words. De-formation implies that it was well-formed before. Not every change of form however is a de-formation. It includes judgment from “better“ to “worse“.
marky1991 1 days ago [-]
I don't think so, 'deformation' can also just mean any arbitrary change of shape, and in a physics/engineering context, that's usually all it means.
From websters:
1. alteration of form or shape
also : the product of such alteration
2: the action of deforming : the state of being deformed
3: change for the worse
so it's just sense 1.
PaulDavisThe1st 1 days ago [-]
In english, the word is almost always used to refer to "alteration of form or shape" away from the default form or shape.
kergonath 1 days ago [-]
Not really in mechanics (or geophysics). Most of the time there is no sensible default, and we talk about reference instead. But then that’s just muddying the waters. Here, "default" is utterly meaningless, for example.
The long and short is that deformation means just that the shape of something changes.
In other words, sound (seismic waves) travels much faster in one direction than the other through the inner core. That's true of most rocks to some degree, and it implies that the crystalline iron in the inner core is mostly aligned in a similar direction. But that is at the core (pun intended) of all of this.
So the "fast direction" has subtly changed over time based on the data we have. That's the "the Earth's inner core rotates differently than the rest" part. But we're mostly basing that on travel times in each direction (it's more complex than that - more in a bit). The differences "more fast stuff" and "less slower stuff" are hard to distinguish precisely, though they can be distinguished because of effects that occur at the boundary between different velocity + density bodies. It's also harder because the outer core is liquid and removes a key source of information coming from wave interactions at those boundaries (shear waves).
This is basically doing a lot of clever reprocessing of old data to carefully look data after corrections for the moderately-well-constrained rotation of the inner core. Rotation of the inner core can't explain all of the differences, so another thing that might cause it is changes in the shape of the boundary between the inner and outer core. It's also possible it's noise, though presumably the authors investigated that part carefully (haven't read the scientific article, but the primary author is a very well known person in the field, so the analysis is likely very sound).
There are always alternate explanations, though. Changes in shape on the order called for here do need an explanation via geological processes. Kilometer scale changes in a decade are difficult to immediately explain, though not impossible. I have no doubt the analysis is sound, but from a geologic perspective, this (and previous) work raises a lot of interesting questions.
Would also fit the weird events in Italy's Campi Flegrei and Greece's Santorini island recently.
No, I'm not serious :)
https://www.imdb.com/title/tt0298814/
https://xkcd.com/1387/
From websters:
so it's just sense 1.The long and short is that deformation means just that the shape of something changes.