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This article shows the layers of the Earth as being perfectly spherical, like the oblate spheroid that is the top layer of Earth's crust. Little 8km high Everes

This article shows the layers of the Earth as being perfectly spherical, like the oblate spheroid that is the top layer of Earth's crust. Little 8km high Everest mountain ranges or 8km deep Mariana trenches are peach fuzz on the 12,750 km diameter billiard ball, and I suppose it seems reasonable to assume that the mantle and core beneath are similarly shaped by gravity to near-perfect spheroids. But I recently learned about the African and Central Pacific mantle plumes, which rise far above the circles in those Pac-man renderings: https://www.theatlantic.com/science/archive/2020/01/seismic-mystery-underneath-africa-and-pacific/604729/ https://www.theatlantic.com/science/archive/2020/01/seismic-... I expect that's old news to someone in the field, but I haven't thought critically about that diagram since high school.

itronitron 4y ago
I don't know why, but it took me a full minute to realize that graphic was spinning in a counter-clockwise fashion.
- dylan604 4y ago
  What would you expect for a planet where the sun rises in the east and sets in the west?
  - bregma 4y ago
    A plane, like the Earth, with the sun appearing and disappearing over the edge.
    - dylan604 4y ago
      see, the flat earthers have it all wrong, which is evident by this comment. clearly, it is the sun that is traveling around the earth. i mean, if it disappeared, it wouldn't be coming back. so at least my theory is much more logical. and mars just likes to screw with us by reversing course a couple of times just to see if we're paying attention
      - int_19h 4y ago
        It's a different sun every day, duh.
  - itronitron 4y ago
    I think because the continents fade out as they approach the point closest to the viewer it makes it look like they are actually fading into the background and behind the red blobby thingies.
  - jobigoud 4y ago
    I wonder if people in the southern hemisphere think of it as rotating clockwise?
    - dylan604 4y ago
      east is east and west is west, even if you're standing on your head
      - jobigoud 4y ago
        If you are in space and you look at the Earth from below it's rotating clockwise in space. It's only counter-clockwise when you look from above.
    - seanhunter 4y ago
      Tldr: No they don't. (Speaking as someone who grew up in the Southern hemisphere and now lives in the Northern). Long version: I mean, there might be some who do but that's true of any deliberately perverse opinion[1]. I expect that generally people think of the Earth's direction of rotation as being from East to West and if they were trying to get to clockwise/anticlockwise they would specify which pole they were standing at. [1] You can make a clock that rotates counterclockwise[2] but that doesn't prove that words have no meaning, just that you're a curmudgeon. Most people would concede they know what you mean when you ask whether the earth rotates clockwise or anticlockwise and that wouldn't vary between Southern and Northern hemisphere dwellers I think. [2] which is an interesting philosophical/linguistic conundrum because isn't the direction of rotation of a clock by definition "clockwise" whichever direction it rotates? It is a clock after all.
- alecbz 4y ago
  Same -- I think something about the graphic (maybe how it blends in with the background in place?) creates that kind of "spinning balerina" illusion.
- powersnail 4y ago
  I would guess it's the fact that the farther side looks brighter than the nearer side. Animated 3D rotation without any shading or shadow always throws me off for a second. If the inside of the globe is slightly opaque, dimming the farther side proportionally, it might make it easier.
jofer 4y ago
Mantle plumes don't significantly change the shape of the core or mantle, though. They're convection within the mantle. They rise from the core mantle boundary, but they're basically temperature features, not structural features. In other words, mantle plumes are parts of the mantle that are hotter than the other identically composed mantle around them. In contrast, the core and the crust are different compositions than the mantle. Just to clear up another common confusion, the mantle is very much solid, except for a tiny fraction of melt in a narrow and shallow zone called the athenosphere. The mantle flows over time despite being solid, though (think of a glacier). Just like a marble slab will bend over time (see benches in old graveyards that sag in the middle), the mantle slowly flows, but a hammer/etc would bounce right off of it. That's also true of large portions of the crust. As far as how smooth or not smooth the actually core boundaries are, we don't really know in detail. To a first order, they're smooth (i.e. we measure a broadly consistent radius from multiple directions), but that doesn't mean they're necessarily a "billard ball". There's likely fairly complex topography at the boundary that we can't easily measure.
- hcrisp 4y ago
  Does the athenosphere produce surface lava?
  - jofer 4y ago
    That's a surprisingly complex question. The best answer is probably "sometimes". The chemistry of volcanic rocks gives a lot of clues as to the origin of the melt. The athenosphere is actually a bit poorly defined in this sense (it's a mechanical classification, not a chemical classification). Regardless, it's easy to distinguish magmas with a pure mantle source from others. MORB (mid ocean ridge basalt) is a common acronym for volcanic rocks with a chemistry that indicates they're essentially pure mantle melt. In the most common type of volcanoes you see on land (arc volcanoes), magma forms due to the introduction of water and other volatiles that lower the melting point of the upper mantle. That's what happens at arc volcanoes like the Cascades or Mt Fuji in Japan. It's not exactly coming from the athenosphere in that case, and it's often the lithospheric mantle and lower crust that are being melted. It's not heat that causes it, but instead the introduction of water. Volcanoes can also form due to the introduction of extra heat, as happens above hotspot volcanoes (e.g. the Galapagos or Hawaii). In many of those cases, you're basically seeing the athenosphere supplying extra heat to the mantle lithosphere and crust and melting it. The magma usually isn't coming directly from the athenosphere in those cases (though some of it can and does). However, flood basalts are an extreme case of hotspots, and their chemical signatures suggest that it's more or less melt directly from the athenosphere. Finally, one of the most common types of volcano on the planet does come directly from the athenosphere: mid ocean ridge systems. (Where the term MORB comes from) Those are almost entirely deep in the oceans, so non-geologists don't think about them as much, but they make up the bulk of volcanic activity on Earth. In those cases, you're essentially bringing the athenosphere up and melting more and more of it as it rises. Those are the cases where magma is most directly sourced from the athenosphere.
deleted 4y ago
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anshumankmr 4y ago
This seems like a fantastic prompt for a sci fi novel.
simonh 4y ago
I don't think it's really fair to say that. The difference in diameter across the axes is about a third of a percent. Given the size of the image, that's about 2 pixels. I think you're being a bit optimistic expecting to be able to perceive that with the naked eye.
deleted 4y ago
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dmix 4y ago
https://archive.is/2020.01.11-165451/https://www.theatlantic.com/science/archive/2020/01/seismic-mystery-underneath-africa-and-pacific/604729/ https://archive.is/2020.01.11-165451/https://www.theatlantic...
_8j50 4y ago
Counter argument here is that being encased in hot liquid magma and rotating for a long time might force it to be a perfect spheroid?
jvm___ 4y ago
The thickness of the outer crust is easy to visualize. It ranges from a few minutes walk to an hour at city street speeds. Nothing close to 12,000kms. "Under the oceans (and Hawaiian Islands), it may be as little as 5 kilometers (3.1 miles) thick. Beneath the continents, the crust may be 30 to 70 kilometers (18.6 to 43.5 miles) thick."

itronitron 4y ago

I don't know why, but it took me a full minute to realize that graphic was spinning in a counter-clockwise fashion.

dylan604 4y ago
What would you expect for a planet where the sun rises in the east and sets in the west?
- bregma 4y ago
  A plane, like the Earth, with the sun appearing and disappearing over the edge.
  - dylan604 4y ago
    see, the flat earthers have it all wrong, which is evident by this comment. clearly, it is the sun that is traveling around the earth. i mean, if it disappeared, it wouldn't be coming back. so at least my theory is much more logical. and mars just likes to screw with us by reversing course a couple of times just to see if we're paying attention
    - int_19h 4y ago
      It's a different sun every day, duh.
- itronitron 4y ago
  I think because the continents fade out as they approach the point closest to the viewer it makes it look like they are actually fading into the background and behind the red blobby thingies.
- jobigoud 4y ago
  I wonder if people in the southern hemisphere think of it as rotating clockwise?
  - dylan604 4y ago
    east is east and west is west, even if you're standing on your head
    - jobigoud 4y ago
      If you are in space and you look at the Earth from below it's rotating clockwise in space. It's only counter-clockwise when you look from above.
  - seanhunter 4y ago
    Tldr: No they don't. (Speaking as someone who grew up in the Southern hemisphere and now lives in the Northern). Long version: I mean, there might be some who do but that's true of any deliberately perverse opinion[1]. I expect that generally people think of the Earth's direction of rotation as being from East to West and if they were trying to get to clockwise/anticlockwise they would specify which pole they were standing at. [1] You can make a clock that rotates counterclockwise[2] but that doesn't prove that words have no meaning, just that you're a curmudgeon. Most people would concede they know what you mean when you ask whether the earth rotates clockwise or anticlockwise and that wouldn't vary between Southern and Northern hemisphere dwellers I think. [2] which is an interesting philosophical/linguistic conundrum because isn't the direction of rotation of a clock by definition "clockwise" whichever direction it rotates? It is a clock after all.
alecbz 4y ago
Same -- I think something about the graphic (maybe how it blends in with the background in place?) creates that kind of "spinning balerina" illusion.
powersnail 4y ago
I would guess it's the fact that the farther side looks brighter than the nearer side. Animated 3D rotation without any shading or shadow always throws me off for a second. If the inside of the globe is slightly opaque, dimming the farther side proportionally, it might make it easier.

jofer 4y ago

Mantle plumes don't significantly change the shape of the core or mantle, though. They're convection within the mantle. They rise from the core mantle boundary, but they're basically temperature features, not structural features. In other words, mantle plumes are parts of the mantle that are hotter than the other identically composed mantle around them. In contrast, the core and the crust are different compositions than the mantle. Just to clear up another common confusion, the mantle is very much solid, except for a tiny fraction of melt in a narrow and shallow zone called the athenosphere. The mantle flows over time despite being solid, though (think of a glacier). Just like a marble slab will bend over time (see benches in old graveyards that sag in the middle), the mantle slowly flows, but a hammer/etc would bounce right off of it. That's also true of large portions of the crust. As far as how smooth or not smooth the actually core boundaries are, we don't really know in detail. To a first order, they're smooth (i.e. we measure a broadly consistent radius from multiple directions), but that doesn't mean they're necessarily a "billard ball". There's likely fairly complex topography at the boundary that we can't easily measure.

hcrisp 4y ago
Does the athenosphere produce surface lava?
- jofer 4y ago
  That's a surprisingly complex question. The best answer is probably "sometimes". The chemistry of volcanic rocks gives a lot of clues as to the origin of the melt. The athenosphere is actually a bit poorly defined in this sense (it's a mechanical classification, not a chemical classification). Regardless, it's easy to distinguish magmas with a pure mantle source from others. MORB (mid ocean ridge basalt) is a common acronym for volcanic rocks with a chemistry that indicates they're essentially pure mantle melt. In the most common type of volcanoes you see on land (arc volcanoes), magma forms due to the introduction of water and other volatiles that lower the melting point of the upper mantle. That's what happens at arc volcanoes like the Cascades or Mt Fuji in Japan. It's not exactly coming from the athenosphere in that case, and it's often the lithospheric mantle and lower crust that are being melted. It's not heat that causes it, but instead the introduction of water. Volcanoes can also form due to the introduction of extra heat, as happens above hotspot volcanoes (e.g. the Galapagos or Hawaii). In many of those cases, you're basically seeing the athenosphere supplying extra heat to the mantle lithosphere and crust and melting it. The magma usually isn't coming directly from the athenosphere in those cases (though some of it can and does). However, flood basalts are an extreme case of hotspots, and their chemical signatures suggest that it's more or less melt directly from the athenosphere. Finally, one of the most common types of volcano on the planet does come directly from the athenosphere: mid ocean ridge systems. (Where the term MORB comes from) Those are almost entirely deep in the oceans, so non-geologists don't think about them as much, but they make up the bulk of volcanic activity on Earth. In those cases, you're essentially bringing the athenosphere up and melting more and more of it as it rises. Those are the cases where magma is most directly sourced from the athenosphere.

deleted 4y ago

[deleted]

anshumankmr 4y ago

This seems like a fantastic prompt for a sci fi novel.

simonh 4y ago

I don't think it's really fair to say that. The difference in diameter across the axes is about a third of a percent. Given the size of the image, that's about 2 pixels. I think you're being a bit optimistic expecting to be able to perceive that with the naked eye.

deleted 4y ago

[deleted]

dmix 4y ago

https://archive.is/2020.01.11-165451/https://www.theatlantic.com/science/archive/2020/01/seismic-mystery-underneath-africa-and-pacific/604729/ https://archive.is/2020.01.11-165451/https://www.theatlantic...

_8j50 4y ago

Counter argument here is that being encased in hot liquid magma and rotating for a long time might force it to be a perfect spheroid?

jvm___ 4y ago

The thickness of the outer crust is easy to visualize. It ranges from a few minutes walk to an hour at city street speeds. Nothing close to 12,000kms. "Under the oceans (and Hawaiian Islands), it may be as little as 5 kilometers (3.1 miles) thick. Beneath the continents, the crust may be 30 to 70 kilometers (18.6 to 43.5 miles) thick."