GeoGeoGeoGeo t1_j5suvl3 wrote

There is a suggested different spin rate between the inner solid core and liquid outer core. The difference, however, is exceptionally small, and they both rotate at the same speed to within 0.001%.

The difference in speed is believed to be a result of two competing forces: The gravitational tug of the surrounding mantle, and the torque induced by the electromagnetic field from the outer core.

So when they report that its stopped spinning they mean relative to the mantle, same as when they say its reversed, and sped up.


GeoGeoGeoGeo OP t1_j2twr06 wrote

Glad to hear it! There are so many things I still find mind blowing or hard to grasp in geology, it's such a fantastic field of study. TPW is also thought to have occurred on Mars as well^1, ^2


GeoGeoGeoGeo OP t1_j2tjpsh wrote

That was actually my comment above explaining the differences between ATP and TPW and the theoretical speed limits to TPW (not that actual reported rate in the study, which was 40–50° over 10 million years or upwards of 55.5 cm/yr).

Interesting. As is the case with most conspiracy theories perhaps one or more of the individual components are correct on their own, but the details, mechanisms, and relationships between their interactions are woefully lacking in understanding.


GeoGeoGeoGeo OP t1_j2szzlb wrote

In fact it might just be, but not for your rock collection... for water.

>"The significance of finding opal on Mars will have advantages for future astronauts, and exploration efforts could take advantage of these widespread water resources. Opal itself is made up of predominantly two components: silica and water, with minor amounts of impurities such as iron. Since opal is not a mineral, the water is not bound as tightly within a crystal structure. This means that if you grind it down and apply heat, the opal releases its water. In a previous study, Gabriel and other Curiosity rover scientists demonstrated this exact process... a single-meter halo could house roughly one to 1.5 gallons of water in the top foot of the surface. Combined with growing evidence from satellite data that shows the presence of opal elsewhere on Mars, these resilient materials may be a great resource for future exploration activities elsewhere on Mars — that is, if opal elsewhere on Mars also retains water to the same degree as the opal in Gale Crater."


GeoGeoGeoGeo OP t1_j2qjl16 wrote

As to whether or not this would increase intraplate or marginal plate stress I really have no idea. If the plates don't move perfectly synchronously with one another there might be a bit of a jostling around per se. If there were, 677.1cm/yr (22 ft./yr) is potentially a lot of increased seismicity / strain within any infrastructure adjacent to or spanning major fault systems, along with subsequent increase in associated natural hazard risks. All that being said, TPW is effectively a decoupling of the fluid outer core to the silicate Earth (mantle and crust) so it really may be a bit of a stretch to think that there may be increased seismicity. Certainly interesting to ponder.


GeoGeoGeoGeo OP t1_j2q8pv6 wrote

Apparent Polar Wander vs True Polar Wander:

Apparent polar wander (APW) occurs as the magnetic pole drifts about the surface of the Earth, this is why your compass needs to account for declination. APW is associated with reversals of the geomagnetic field. True Polar Wander (TPW), on the other hand, is a re-orientation of the solid Earth as a whole relative to the spin axis. On Earth, TPW is achieved by wholesale rotation of the solid, silicate Earth (mantle and crust) around the liquid outer core. As Earth’s magnetic pole is tied primarily to rotationally induced excitations of the outer core, the magnetic poles remain aligned with the rotation axis through a TPW event. For example, 90° of TPW could result in Antarctica moving to the equatorial region, Africa moving to the pole, and all other geographic features moving accordingly. Theoretical constraints demonstrate that TPW can occur quite rapidly, limited to approximately 61° in 100 million years (Ma) and 8° in 10 Ma (Theoretical constraints on true polar wander). 1° latitude ≈ 111 km. 61° per Ma ≈ 6771 km per Ma or 677.1 cm per year and 8° in 10 Ma is ≈ 88 cm per year. Those rates are exceptionally fast when compared to tectonic speed limits (Tectonic speed limits from plate kinematic reconstructions) and modern rates of plate motion; The Cocos and Nazca plates (in the pacific ocean) are right now the quickest, moving at over 10 cm per year.

EDIT: An analogy for further clarity and distinction between APW and TPW: Think of a hot slice of cheese and pepperoni pizza with a laser pointing up from below. The pizza sauce is Earth's mantle, and the cheese and pepperoni toppings are the continents. If you were to shoot a laser upwards, from below the pizza slice, you could trace the movement of the laser by looking at the trail it left behind on the toppings. In this scenario, the magnetic pole (the laser) moved but the continents (the toppings) remained in their positions. TPW on the other hand would be like picking up a hot slice of pizza and the toppings all sliding off in one direction at the same time. The laser from below would still leave a trace on the toppings but this time it was the toppings that moved instead of the laser.


GeoGeoGeoGeo OP t1_j1g458e wrote

What I find interesting is the fault(s) depicted in the mantle. At those depths, beyond the brittle-ductile transition I would have expected the rocks to deform plastically as opposed to brittle deformation. Is it mylonitic? Can mylonites have seismicity?


As previously assumed, brittle deformation doesn't occur in the lithospheric mantle so I think it's assumed that seismic anisotropic reflectors (generated from crystallographic preferred orientations) in the lithospheric mantle arise from grain size reduction via dislocation and diffusion creep along grain boundaries. These seismic anisotropic reflectors are thus interpreted as fine grained mylonitic shear zones and thus downward extensions of brittle faults across the brittle-ductile transition from the crust into the mantle.

Now I'm curious as to how these mantle shear zones, a ductile feature in a ductile regime, remain long lived enough to act as pathways for magma ascent...


GeoGeoGeoGeo OP t1_j1blucb wrote

Saying it gets to the surface doesn't explain how it gets to the surface, and if I asked you to draw the plumbing system for its pathway to the surface I'd be willing to bet that you'd be pretty far from the truth. This study helps resolve that plumbing system which was pretty uncertain previously.


GeoGeoGeoGeo OP t1_iyo1hxi wrote

People have drilled directly into magma before (Hawaii in 2007? & Iceland 2009), and there has been no eruption for a couple of reasons:

(1) drill holes are too narrow to transmit the explosive force of a volcanic eruption. (It’s the equivalent of piercing a champagne cork with a pin rather than removing the entire cork at once.)

(2) Due to the small diameter of drill holes (typically <10 cm), the small amount of magma that could flow into the shaft would solidify long before reaching the surface

See Iceland Deep Drilling Project:The first well, IDDP-1, drilled into Magma for more information.


GeoGeoGeoGeo OP t1_iykh0uc wrote

> It's incredibly easy to see areas that have older ice breaks that have completely shifted due to later plate shifting.

That's not true at all as is evident from the article itself had you cared to read it:

"... to best reconstruct the motion of the surface, large areas suspected to be plates in previous studies had to be broken into smaller subplates along less obvious boundaries. This observation helps explain why some prior studies found that large plates did not reconstruct well or behaved in other unexpected ways..."

>Not sure why someone would write a paper on something that's already so well known and easily seen / understood.

Contrary to your claim, this subject is not well known, easily seen or understood and is why researchers continue to refine their models. The fact is that this is still a very new subject (plate tectonics via ice) with little data comparatively speaking. I'll further add that plate tectonics on Earth is still a subject that continues to be refined as new methods are developed, and more data presented.