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:
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.
If you take a real well-played snooker ball, it has plenty of tiny but visible scratches, say, 0.25 mm deep.the ball's diameter is 52.5 mm, so the scratches depth is about 1/200 of its diameter. If we take Earth's diameter as 12750 km, scratches like that would be features about 63 km tall, nearly an order of magnitude larger than tallest mountains on Earth. If course the mantle is smaller diameter, but unless we cannot detect roughly 50 km-tall ridges (I don't know much about seismic wave registration), it's about as smooth as a billiard ball %)
> Just like a marble slab will bend over time (see benches in old graveyards that sag in the middle), the mantle slowly flows
I had to see more of this, and it took me a while because most results are about construction and marble products. It looks like thin slabs of marble bow because of microfractures and internal stress, not by flowing.
> In other words, mantle plumes are parts of the mantle that are hotter than the other identically composed mantle around them.
The parent's link suggests that alternate views exist, that the mantle plumes are indeed chemically distinct from the surrounding rock.
From the linked article:
This suggests that the edges of the blobs mark a transition between materials, not just temperature.
In this view, the blobs are so-called thermochemical piles, clumps of dense rock with a distinct chemical composition. Because of their prolonged contact with the core, they are hotter than the rest of the mantle, causing plumes to sprout.
Yes, there's a chemical component as well. I was simplifying. Regardless, though, they're not core material rising up. They're still basically olivine+pyroxenes+etc, same as what's around them. They're not the exact same, and indeed they bring deep mantle material up, but they're not nickle-iron rising up from the outer core, which is what I was trying to get across.
>They rise from the core mantle boundary, but they're basically temperature features, not structural features.
my understanding was that this was not actually a settled topic, and there was ongoing debate as to whether or not they were thermochemical structures, with the main evidence against them being "basically temperature features" the fact that they're not a classic plume shape
Yeah, it's far from settled in detail, and for a long time there was a camp that maintained that mantle plumes did not really exist in the normal sense.
However, further imaging work seems to show that 1) they actually do seem to be a classic plume shape in many cases (or, more precisely, have complex shapes compatible with convection), and 2) most do have temperature anomalies associated with them. Some things we thought were plume related may not be, but folks are much more in agreement that they look a lot more like convection-related features.
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.
I'm curious how water would lower the melting point of solid rock. I'm aware that adding ethanol to water lowers the boiling point of the resulting solution, but that's a combination of two liquids. I can't think of a physical mechanism where adding a liquid to hot solid rock results in hot liquid rock.
Where does the water come from? Is it liquid, or gaseous?
It's more or less the same way putting salt on ice causes it to melt. Diffusion still occurs with solids, just at a lower rate than with liquids.
As for whether it's liquid or gaseous, I probably shouldn't have called it "water", and should have said "hydrogen and oxygen in silicate minerals". Silicates always have oxygen, but some hydrogen too (hydroxyl groups - i.e. OH).
Basically, you have minerals that transform to other minerals at depth due to the pressures and temperatures involve. That transformation leads to the release of hydrogen and oxygen as they're in one crystal structure and not in the other. (Basically, minerals with hydroxyl groups transform into minerals that do not have hydrogen in their composition, releasing hydrogen and oxygen in the process.) That hydrogen and oxygen diffuses into adjacent mineral crystals and can cause them to melt.
With that said, any time you have magma (i.e. melt), it's going to have H2O, CO2, halogens, etc dissolved in it, just like water has oxygen and carbon dioxide dissolved in it. We talk about these in simple terms of "H2O" and "CO2" etc, but often the details of how things are bonded are a bit different, just like CO2 dissolved in water isn't exactly CO2, but is carbonic acid (H2CO3) instead.
Think of how adding water to hot sugar reduces the melting point of sugar. Sufficiently large amounts of water reduces the melting point to room temperature (also known as dissolving the sugar.)
That's a really interesting link, but I don't think it's really the same process, or answer my objection. I don't think "melting point" is the right concept for the phenomenom of combining water and sucrose crystals.
When sugar dissolves in water, it creates a solution, a chemical mixture characterized in this case by ionic bonds between water molecules and sucrose molecules. In general, the melting and boiling points of a solution will not be the same as the melting and boiling points of any of the individual substances that comprise the solution.
When I think about combining substances, I think about suspensions, solutions, colloids. (When I think about combining substances, I'm usually thinking about cooking). A suspension is small particles mixed into a liquid, but it isn't stable; after time or with a centrifuge, you can separate them back out. A solution is a chemical bond between individual particles of each substance, such that it is stable. A colloid is small particles mixed into a liquid or gas, but the small particles are so small that it is stable and cannot easily be separated out. Here's the link I used to refresh my memory enough to explain these concepts: https://lab-training.com/understanding-differences-solutions...
I'm sure you're aware of all that, but I wanted to write it out so I could be more explicit about my confusion. Adding water to solid rock will not result in a solution, colloid, or suspension. Adding finely ground rock and water can do so; that's kind of what mud or clay is. So I was confused how adding water to rock could result in any kind of mixture that changes the melting point of the rock.
Jofer's explanation makes sense to me: it's not actually adding H2O molecules to solid rock. Instead, it's that certain minerals under sufficient heat and pressure change mineral/crystal structure in a way that results in the precipitation/expulsion of various molecules and ions, including hydrogen and oxygen. Those precipitates diffuse through the solid until they react and combine with other minerals, causing transformations of those into new mineral/crystal structures with a lower melting point.
The link you provided talked about how solutions of sucrose and water in differing concentrations have different melting points, but I was confused about how rock and water could dissolve at all.
The bonds between water and sugar molecules are not ionic, they're hydrogen bonds. These are also the bonds between sugar molecules.
The general thing that is happening is this: water allows the sugar molecules to separate without paying as large an energy penalty. This means the higher entropy of disordered sugar molecules allows that energy penalty to be overcome at lower temperature (and/or higher concentration, which reduces the entropy increase.)
The same thing is happening with water and rock, if not by exactly the same mechanism. Water reduces the energy cost of breaking bonds in the rock (covalent Si-O bonds, not hydrogen bonds).
Adding water to rocks does result in a solution. Rock is very slightly soluble in water. It's just that at normal temperature and pressure the solution is extremely dilute. This is because the energy penalty is so high that a very large entropy increase is needed to overcome it, and the entropy is logarithmic in dilution. Raise the temperature a bit and the solution becomes more concentrated. This is how quartz is deposited to grow artificial crystals for electronics: it goes into solution in hot, pressurized water and is deposited on seed crystals. This also happens naturally with various minerals (including quartz.)
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."
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.
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.
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.
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
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.
This page is very rough and shouldn't be considered scientific. I didn't even find a link or the actual study name on the page. Not only that, Dr. Thanh-Son Pham is listed as a co-author but the page doesn't even mention the name of the second author, Hrvoje Tkalčić.
I was able to find the home page for Dr. Thanh-Son Pham [1] and his google scholar page with his list of publications. [2] He looks extremely accomplished and a prolific researcher, especially for someone who appears to be so young. I was very impressed and can only think that others would have also liked to have a link to this paper. I found the actual paper online. [3]
Abstract:
Probing the Earth’s center is critical for understanding planetary
formation and evolution. However, geophysical inferences have been
challenging due to the lack of seismological probes sensitive to the
Earth’s center. Here, by stacking waveforms recorded by a growing
number of global seismic stations, we observe up-to-fivefold
reverberating waves from selected earthquakes along the Earth’s
diameter. Differential travel times of these exotic arrival pairs,
hitherto unreported in seismological literature, complement and
improve currently available information. The inferred transversely
isotropic inner-core model contains a ~650-km thick innermost ball
with P-wave speeds ~4% slower at ~50° from the Earth’s rotation axis.
In contrast, the inner core’s outer shell displays much weaker
anisotropy with the slowest direction in the equatorial plane. Our
findings strengthen the evidence for an anisotropically-distinctive
innermost inner core and its transition to a weakly anisotropic outer
shell, which could be a fossilized record of a significant global
event from the past.
Yeah it looks like that website just stole the text from CNN and omitted a bunch of it. CNN didn't interview the other authors, but at least their figures are properly attributed (all tagged with Drew Whitehouse/Son Phạm/Hrvoje Tkalčic -- Whitehouse apparently works for National Computational Infrastructure and did the visualizations)and they directly link to the study.
My current fun internet science quest it reading papers about how much iron is in the sun, or perhaps better said as how big is the iron core in the sun.
this has been especially fun because the answers ranges from fractional percentages to most of it.
The most of it theory says that the sun is a stellar remnant, but I think fusion would suffer if that were the case.
The fractional percentage theory is based off of the observed spectra of the sun.
The sizable iron core theory is based off of the observed atomic composition of the inner solar system. there are also missing neutrino observations that support this theory, that is, there are not enough observed neutrinos that match a hydrogen core but do match an iron core.
Like I said a fun subject, I love it when an innocent question "How much iron is in the sun?" leads to such wildly different theories.
Wait.. what? Stellar remnant? I've never heard any talk at all that our sun is that far along in it's stellar evolution. Is that legitimate or some whacky stuff.
It is hard to tell until you read enough literature!
That is the tricky part about following science as a layperson; a bad sample can give you a distorted view, leaving you thinking a fringe view not supported by the data is plausible or correct.
It is a crank theory, untrue, but it goes. What happened to the core of whatever star exploded to form the gas cloud that formed the solar system, why would that core not be the gravitational locus of the new star.
Supernovae spread mass over hundreds of light years. And then things start drifting apart. Whatever exploded to leave behind the mass that created the Earth and the Sun could be thousands of light years away.
I don't know what you are reading but the sun is absolutely not a stellar remnant. It really should not have much iron in it as it is still happily fusing hydrogen. Stars don't create iron until they run out of hydrogen.
EDIT: After googling I found an article about this crank Dr. Oliver Manuel. I hope you aren't getting ideas from him.
Jupiter has an iron core, Mars has an iron core, Earth has an iron core, Venus has an iron core, Mercury has an iron core. and you are telling me that despite the solar system being formed out of the same gas cloud there is no iron core in the sun. I agree that it could not be too large or fusion would suffer, but at this point I am convinced there is one.
The stellar remnant theory, is a bit stupid, but fun science fiction, the solar system is a second generation star system, the presence of iron and heavy metals confirms that. The question then is what happened to the core of whatever star exploded to make the gas cloud that formed the solar system. why would it not form the gravitational center of a new star? This is unlikely because I think that fusion, if any, would be noticeably weird.
I did find some papers by Dr. Oliver Manuel, I agree, a crank, however there are some interesting questions raised.
Does seem pretty whacky. But I'm quite ignorant in this area - it is interesting that all the heavy elements in the earth we are told come from a super novae. What is the traditional theory for how the planets of our solar system, orbiting around a hypothesized second generation star came to be endowed with those elements? The idea that we are literally formed directly from the remnants of a supernovae is alluring even if I have no formal training in the field.
"it is interesting that all the heavy elements in the earth we are told come from a super novae"
The origin of heavy elements is actually more complex than that.
All of the hydrogen and most of the helium in the universe emerged 13.8 billion years ago from the Big Bang. The remainder of the chemical elements, except for a tiny amount of lithium, were forged in stellar interiors, supernova explosions, and neutron-star mergers. Elements up to and including iron are made in the hot cores of short-lived massive stars. There, nuclear fusion creates ever-heavier elements as it powers the star and causes it to shine. Elements heavier than iron—the majority of the periodic table—are primarily made in environments with free-neutron densities in excess of a million particles per cubic centimeter. The free neutrons, if captured onto a seed nucleus, result in a heavier, radioactive nucleus that subsequently decays into a stable heavy species. The so-called slow neutron-capture process, or s-process, mostly occurs during the late stages in the evolution of stars of 1–10 solar masses (M⊙). But the s-process accounts for the formation of only about half of the isotopes beyond iron. Creating the other half requires a rapid capture sequence, the r-process, and a density of greater than 1020 neutrons/cm3 that can bombard seed nuclei. The requisite neutron fluxes can be provided by supernova explosions (see the article by John Cowan and Friedrich-Karl Thielemann, Physics Today, October 2004, page 47) or by the mergers of binary neutron-star systems.
Ditto. I look at porn, but this is the first time I've seen a hentai ad attached to an innocuous article. The hentai ad is non-nude but says it's for adults.
Turned my ad blocker off to try it and, sadly no NSFW ads for me. Some ads for cool looking redwood gazebos and patio roofs, and boomer-themed t-shirts. I'm disappointed my profile is so boring.
As someone who "appreciates" hentai, I am disappointed after 10 page reloads that I didn't get anything remotely related to anime ads. I just installed a new chrome browser though, so I don't I haven't installed adblock yet. More importantly, the link article is pretty much an adspam, every corner there is an ad.
Earth’s diameter is around 13000km, if there is an inner core with a 600 km width, you will find this core around 6000km below your feet, which is more than 1600 km below your feet (as the article correctly stated…)
Yes, I also noticed it. It's too large a difference to be some miles to km conversion mistake. There is nothing 1600 km wide inside [1], not even the distance between the inner core and this new inner-inner core boundaries.
I do think conversion is involved in generating these odd figures somehow. May not be the sole part, but the figure in the title is definitely an conversion that's sprouted additional sigfigs.
Typo there: 400 miles. The actual paper's abstract [1] says "~650-km". In a skim through I didn't see anything that might correspond to the strange 1600km depth.
It's a weird article/website -- they just stole most of the text from CNN. Including a section where they say, "Geoscientists first suggested that Earth’s core might have an imperceptible extra layer about 20 years ago, according to a press release leaked to CNN News."
There's no hint of who runs it/operates it -- is it some sort of auto-plagiarizer?
Wait, I definitely remember reading about this in science magazines years ago: the earth's core is more like solid than liquid because it's under tremendous pressure from gravity, and it's spinning, and it's iron, which is why Earth has a magnetic field.
Is the new discovery that there is actually a fifth layer, which is solid, and that what we previously thought of as the "core" is actually liquid and not the innermost layer?
It's been known for decades that the Earth's core (which is mostly iron and nickel, as opposed to the mantle which is made of silicates) has a liquid outer layer and a solid inner layer. This is apparent because seismic shear waves can propagate through the inner layer but not the outer layer, which is diagnostic of the medium being liquid and not solid. (The shear or S-waves get to the inner core because when a seismic pressure wave, which can travel through liquid, hits the inner-core-outer-core boundary, some of the energy is converted into shear waves. Jofer please correct me if this is inaccurate.)
This article states that the inner core has two different concentric zones that have very different crystalline properties. In particular, the inner sanctum is anisotropic with respect to seismic wave propagation, and the outer sheath of the inner core is much more isotropic. This suggest that they have different geologic histories--the innermost core's crystallographic anisotropy may have resulted from an event early in Earth's history that deformed the crystals, much as mountain building events deform the crystals in Earth's crust and upper mantle. Then, the younger outer sheath of the inner core cooled and crystallized around the older inner bit later on, after the deforming event transpired.
Can you explain a bit more about the difference between the anisotropic and isotopic nature of these different zones?
Are both of these zones “solid” states of matter? Or does our intuition about states of matter not really work for materials at these exotic temperatures and pressures?
No, the Earth's magnetic field isn't because of iron being ferromagnetic, nor does it come from the solid inner core. The iron in the core is well above the Curie temperature at which ferromagnetism ceases.
Rather, the Earth's magnetic field is due to currents flowing in the liquid outer core. Convection in the core drives the conductive metal across these currents, increasing them by a dynamo effect. This process occurs on a rather small scale and is difficult to model, and is also somewhat chaotic, leading to very occasional collapses and flips of the Earth's magnetic field.
It happens on a geological timescale, and is used to help date rocks. The ocean floor is marked with stripes of normal and reversed magnetic polarity (the magnetic field is faintly recorded in magnetization of minerals like magnetite), and this was a strong initial clue that led to the theory of seafloor spreading and plate tectonics.
We are talking about thousands of years for the flip to happen, and hundreds of thousands of years between each flip. We have geological records that it happened, as for the damage, there was a theory that it was linked to mass extinction, but latest research find it unlikely.
It would still be bad for us, but not something worth worrying about right now.
Both meanings were used here. There are electrical currents, and there are flows of material through the magnetic field, producing voltages that sustain currents. The JxB forces also affect the flows. It's a highly nonlinear phenomenon (magnetohydronamics, or MHD).
This reminds me of a paradox in my understanding of gravity. I often read about the pressure inside the earth resulting from the mass above, but the gravitational force inside a spherical shell is zero [0], and the only force acting at a given radius from the center is the mass of the sphere inside that radius.
Think about sinking to the bottom of the Marianas Trench and then inflating a balloon just enough to make you neutrally buoyant. The net force on you will be zero, but you'd still be crushed by the pressure, which is the effect of many kilometers of seawater above you.
Another way to think of this is to imagine a small sphere (like the size of a basketball) around the very center of the Earth. The matter in that sphere feels no net gravitational force, but it has to push back against the entire mass of the rest of the Earth, which is trying to fall into it.
If all the shells above you were self supporting you'd be right, you shouldn't feel any more pressure as you go down, if anything you should feel less force because gravity decreases.
However a shell of liquid is not self supporting, and at the size of a planet pretty much all material behaves like a liquid more or less. This means something needs to be pushing back for the layers of material to stay where they are. That is the pressure you feel, and you can easily show it will increase as you go down (with each layer supporting all the layers above it).
If anything the shell theorem makes this worse because it means the top layer can't pull back on any of the layers below it, it can only be pushed back through sheer pressure.
Same effect is happening inside a black hole, thus each black hole must have a tiny hole inside, with it own event horizon, a bit similar to Arago Spot. :-/
I believe the apparent paradox is that the 'net force' is not the same thing as pressure; it's basically the vector sum of pressure. Pressure in the Earth is an isotropic distribution of stresses, so that in a north-east-up coordinate system, the upward-pushing stress is matched by the downward-pushing stress, the eastward-pushing stress is matched by the westward-pushing stress, etc. So while these sum to zero in some sense, their magnitude is the density of the rock between the point and the surface times the depth times gravity. This is like going deeper in the ocean-the forces are equal in all directions, meaning that they sum to zero in some sense and there is no directional flattening or translation, but they still increase with depth.
> I believe the apparent paradox is that the 'net force' is not the same thing as pressure
I don't think that's what OP means. He's saying that the gravitational force that acts on a given test particle that's located inside Earth at a radius r=R from the center is determined only by the amount of mass "below it", i.e. the mass inside the ball of radius R, not the matter making up the spherical shell R < r < R_E, where R_E is Earth's radius. Put differently, that (hollow) spherical shell does not cause any gravitational force on test particles inside it.
Meanwhile, you are talking about a different thing entirely: The pressure. The matter above (as well as below and next to) our test particle will obviously also experience gravity and get pulled down. So our test particle will experience an isotropic force from all sides, which is generally quantified as pressure (force per area). This pressure is obviously not zero (but no one ever claimed that) and does depend on the radius of the outer spherical shell above it, in the same way as the pressure under water depends on how deep you are.
The net force is 0 in the same way that if two people are pushing you from opposite sides, their net force on you is also zero. You're still being crushed from both sides.
This is a confusion between the gravitational force that the core feels from the layers above, and the pressure that the layers above push down onto the core.
That is, the core doesn't feel gravitational pull towards the outside, because it's balanced on that other side, but the outside is being pulling in towards the core, which pushes on the core.
It might be easier to simplify the mental image by picturing just a slice of the whole thing.
Indeed. The acceleration due to gravity actually increases slightly with depth, reaching a peak at the surface of the core. This is because they Earth's density is not uniform.
The article seems very poorly written. It reads like "We knew that Earth's inner core was a solid ball of iron… but now it's been discovered that the solid ball of iron actually has a solid ball of iron in its core!"
Yeah, I’m kind of scratching my head. This can’t just be a distinction without a difference, can it? Maybe the discovery is that the solid core has two layers of different densities with a gradual “margin” between the two?
Site archyde.com seems to be some kind of weird splog. Is there a better source? What exactly is the new discovery, just that the innermost part of the core has a slightly different composition than the surrounding part?
Is it me, or does 644 kilometers wide seem kind of small for the inner core of the Earth? Does it even stay in place then, or does it kind of drift around slightly within the outer core over time?
That seems like a point of reference thing to me, presumably the iron core is denser than the molten layer around it, gravity is pulling that towards it, but it's all spinning, and there are other gravitational influences from the moon, the rest of the solar system, etc. which could cause some slight sloshing around, I'd bet.
Dumb question but how come we have not yet drilled a hole to the center yet? I know it’s hot af even a few km down and the Russians tried to drill, but wouldn’t that be interesting and a good use of money? Who knows what resources we may actually find down there.
I think a 6000km vertically downward hole is very unstable and will collapse into itself. Any real feasible geometry would just require so much mass redistribution that it might significantly affect the planet's moment of inertia.
Just like with ourselves. For our planet, thoroughly studying the inside of it will probably yield much more interesting results than looking always outside of it.
Look forward to a lot more research about the inner workings of our planet.
Surely the earth's core is a magnet, hence gravitational forces and the ability to actually aggregate all this mass into a sphere and created it's only rotational force.
Yeah, it's a very poorly written article. The actual discovery seems to be that the solid inner core is divided into "outer" and "innermost" inner core, both of which solid iron-nickel but with somewhat different properties and a gradual transition between the layers.
Might there be yet another core (YAC) inside of this new one? Seems that if this was hard to detect the next one will be all the more difficult to find.
I’ve thought about this too, if dark matter is affected by gravity but not other forces, wouldn’t that mean if we were able to drill to the center of any substantial gravity well (say the moon rather than the earth), would we be able to detect a big clump of dark matter? Does that mean there’s a bunch of dark matter at the center of all the stars?
If we assume dark matter is a particle that only reacts via gravity, well, I'm not so sure you will.
The question here is how your particle that only reacts via gravity loses energy. First it will have whatever momentum it has from the galaxy relative to the speed of our solar system and planet. Then as it falls into our gravity well it picks up even more speed. When it reaches the center of our planet it's hauling ass with no brakes so no reason to stop, so it goes screeching out the other side. Even if you somehow had a dark matter particle at 0 relative motion to your gravity well before it fell in, how long is it going to take to bleed off its gravitational energy?
I find the description of dark matter confusing. I hear statements like "dark matter has negligible interaction with ordinary matter". So, how do scientists know that dark matter exists?
"The answer is that our galaxies spin too fast for the visible matter alone to hold them together. Dark matter, which makes up 27% of the universe, provides the additional gravitational force needed. In contrast, visible matter only makes up 5%."
However, I'm left wondering whether dark matter does or doesn't interact significantly with visible matter.
I've always wondered that. like wouldn't uranium, gold, and other heavier elements be more dominant the closer you get to the center of the core? but they are pretty confident on this iron thing
1. There's far less of such heavier elements in the Universe as a whole. Iron is the end-result of all stellar fusion. Heavier elements form only in massive astronomical events --- novas of huge stars, or in neutron-star collisions, black-hole formation, and the like. So most of the heavy stuff is iron or adjacent elements.
2. Most of the heavy stuff most likely is in the inner core, though what the fluid-dynamics of this during and following planet formation are ... is tenuously known at best. Most likely arrived at through modeling and some very limited remote sensing (seismic, neutrino flux), density estimates, and gravimetr (noting differences in Earth's gravitational field).
3. Most of the crustal prevalence of trans-iron elements in the Earth's crust is likely a result of late bombardment. The Giant Impact Hypothesis thought to have formed the Moon may variously account for greater prevalence (more material deposited to the crust from deeper within the Earth) or less (re-liqufication of the crust and mantle leading to more heavy material sinking to greater depths).
4. From an earlier HN thread, @perihelions states that evidence suggests that there's not a sufficient concentration of fissible elements to support sustained nuclear chain reactions within Earth's core, though radioactive decay does contribute about half the source of geothermal energy within the Earth (the other half being latent heat from gravitational energy of formation). See: <https://news.ycombinator.com/item?id=31281424>
Whichever way, generally, yes, heavier elements increase in prevalence with depth.
From Wikipedia:
The core is thus believed to largely be composed of iron (80%), along with nickel and one or more light elements, whereas other dense elements, such as lead and uranium, either are too rare to be significant or tend to bind to lighter elements and thus remain in the crust (see felsic materials).
If only there were a decent way to mine the earth's core directly. There's more usable material already on Earth than the entire asteroid belt. It's just all melted together, molten and buried under thousands of miles of dirt.
If we took the entire core to the surface (without collapsing the Earth which is impossible) we would cover the Earth with iron and nickel to a depth of hundreds of km.
Exactly! Plugging this into Wolfram Alpha reveals that Earth's core is worth $3.268×10^19 (US dollars)[1]. For comparison total global wealth is merely US$431T.
1. thirty-two quintillion six hundred eighty quadrillion dollars
Also, I finally got a workable link. Wolfram really fought me on this one and it shows the dimensionality incorrectly, but the number is correct. 32 trillion trillion dollars (3.2E25). So a hundred times more.
Of course no market would hold a price when flooded with supply, but I bet our appetite for usable energy is higher than iron. That's a harder crystal ball estimation to quantify though.
These calculations are always bogus. Once mining starts, the price of iron will plummet. The exact same reason some reserves are seldom explored, as the decline in price will render the effort pointless.
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-...
I expect that's old news to someone in the field, but I haven't thought critically about that diagram since high school.