I remember reading about the Chandrasekhar limit : as to how a star of a certain mass goes on to become a black hole or explodes in a supernova - depending on its starting mass.
Got me wondering - do we know how theinternal layersof the earth came about ? Is it correct to assume that Earth started out originally with homogeneous structure and over time developed the mantle, crust, etc ? If so - whats the timeline of the current structure ?
Bonus questions : Do all planets in our solar system have internal layers like the earth ? How about stars - do all stars have these layers?
I think all the major planets probably have layers, but not all like the Earth. Some of them are mostly gas. I believe all the solid planets went through a stage of being completely molten, and the layers you are talking about fractionated out in the liquid mix under the influence of gravity. Thus most of the heavy stuff (mostly iron) went to the core.
Of course, most of the layers, the strata, we see in crustal rocks are sediments, formed much later, when things were cool, and most of them under water. (Some are lava flows, and the like.)
Eh, pretty much. The earth (like other planets) formed when little bits of stuff smacked into other little bits of stuff and started clumping together due to gravity. As time went on, more and more bits clumped together, and the earth started getting bigger and bigger.
As the earth grew, heating from compression and from radioactive materials caused it to get hotter and hotter, eventually resulting in what is called the “iron catastrophe”. This is when it got hot enough to melt things like iron and nickel, and that’s when the earth started forming layers. Now that the materials were molten and could move, the heavier stuff like iron and nickel sank, while the lighter materials like silicon and carbon were forced up towards the surface. As the earth cooled, these lighter elements solidified and formed the crust.
Yes, all planets have layers, though as was already mentioned their composition isn’t necessarily at all like the earth’s. Jupiter’s core for example is a dense mass of several different elements surrounded by liquid hydrogen and helium.
Stars also have layers. Stars are great big fusion reactors, fusing hydrogen into helium, and also fusing helium into heavier elements. The heavier elements sink deeper into the core. Like planets, stars also vary in their layers, depending on how big and how old the star is. Older stars will have more heavier elements, as their fusion reactions have been burning for much longer. At the center of a star will be its core, where fusion occurs. Outside of this is a radiation layer, then a convection layer, which are both named for how the energy of the star flows through them. Outside of that you have the photosphere, where photons are generated, then the chromosphere, which is kinda like the star’s atmosphere, and then a super hot region called the corona.
“Homogeneous” isn’t quite the word I’d use for a conglomeration of protoplanets which may, themselves be differentiated, but I think I know what you mean, and yes, the structure developed over time. There was a whole lot of melting going on - radioactive-driven and impact-driven melting.
The Rain-out model suggests just a few dozen millennia after the Earth accumulated, you’d have a core-mantle differentiation. The crust would take longer to form - it requires igneous processes in the mantle that take time - to differentiate out lighter elements - say, 100 Ma.
That’s the theory. Even some planetoids do, like Vesta and Ceres
It’s not quite the same with stars - structure is driven less by compositional differences and more by zones of reaction/energy transfer types, I think. But I’m no expert.
Reading through the history of Geology has left me very skeptical of the claims that seem so obvious. I have a few questions on this and hopefully I can understand better if answered :
When you say grew, do you mean gained mass by other objects joining it - or grew as in expanded due to temperature rise ? Compression would result in shrinking not growing - right ?
Do we know which type of heat dominated ? Radioactive or Compressive ? Did we have enough radioactive material to sustain fusion reactions ? Was this like U-235 or Pu-239 - what elements were they ? Also how much heat is produced by compressive heating of the magnitude on earth - we did not approach a Plasma state or fusion temperatures / densities - did we ?
How do we know that a molten planet will start forming layers ? Is this due to gravity alone - or does the earth’s rotation play a part like a centrifuge ? Also - it would take a lot of conductivity to conduct the heat presumably from the earth’s center to the outside to melt the outer elements. Also, wouldn’t a molten core slow down the radioactive reactions / heat by attenuating neutrons/diluting radioactive pockets ?
Wouldn’t that mean that all the nickel and iron mined on earth/seafloor will roughly occur in the same proportions (since they were well mixed as liquids) in all ores ? We know that is not the case. What gives ?
It likely varied from time to time. And don’t forget impact energy.
Probably some (similar to Oklo) but that wasn’t the main driver. Radioactive elements are just plain hot -as in, physically give off heat - without actually fissioning.
No-one’s suggesting anything near that hot. Just hot enough to melt rocks - and that happens right under your feet, right now.
We know ours did, we know the Moon did, we know Mars did…and we have the physics of it down pat.
Gravity is enough. Density differences can do wonders, even when stuff isn’t molten.
Nickel-iron is plenty conductive. And the melting wasn’t initially only centre-outwards, quite a lot of it happened on the surface first.
Well, yes, notice how the planet* isn’t* a molten cueball these days? That’s because most of the radioactive elements are dissolved in the NiFe core.
No, why would they? Iron ores aren’t derived from the core, they’re derived mostly from dissolved iron that’s precipitated out, or iron oxides in igneous rocks. There’s whole cycles of redistribution and beneficiation at work before you arrive at iron ores. A lot of it geared towards making iron a lot more common than nickel as an ore mineral.
