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New theory explains how Earth’s inner core remains solid despite extreme heat

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Re: New theory explains how Earth’s inner core remains solid despite extreme heat

#11

Post by beevai142 »

technologyvault wrote: post #8

This headline seems a bit overzealous, as if this new theory is the final answer. This new theory, noted as contradicting one from 2014 and 30 years of previous conventional scientific wisdom, came after researchers "looked into larger computational samples of iron than studied previously". What will be the headline and tone in several more years, when someone comes along and studies an even higher number of samples…

I expect the article itself is more carefully worded than the press release.

I don't think people in the scientific community in general really care much about the press releases. The publicity is more something that the funding organizations and universities have started to require in recent years --- you may even get some quantified "career points" of some sort from them depending on the grant. The press releases are at best an afterthought for the researchers. As they are also often edited by the PR staff of the university, there may be some standardized level of hype injected.

Re: New theory explains how Earth’s inner core remains solid despite extreme heat

#12

Post by pdonis »

nonbel wrote: post #2

Something I've been wondering. Does the earth's core have negative heat capacity?[1] I've read that it is usually modeled as a self-gravitating system[2], and that such systems can end up in states with negative heat capacity [3]. [1] > "If the system loses energy, for example by radiating energy away into space, the average kinetic energy actually increases." https://en.wikipedia.org/wiki/Heat_capacity#Negative_heat…

If you look at the Wikipedia article in more detail, you will see that the negative heat capacity of a self-gravitating, isolated system arises from the virial theorem. Heuristically, as a self-gravitating system radiates energy away into space, it becomes more tightly bound; that means it contracts. But as it contracts, the "orbital speeds" of its constituents increase (because decreasing orbital radius means increasing orbital speed), meaning its average kinetic energy increases, meaning it heats up.

Technically, the virial theorem argument only applies to systems whose constituents are in free-fall orbits. But I believe you can do a similar analysis for an isolated self-gravitating system that is in hydrostatic equilibrium--basically, as it radiates energy away into space, the hydrostatic equilibrium changes to one in which the radius is smaller and pressure and temperature are higher. Unfortunately I don't have a handy link to such an analysis right now, though.

As far as whether any of the above would apply to the Earth's core, I don't think it would since the Earth's core is not isolated; but it might apply to the Earth as a whole, to the extent that the Earth can be viewed as being in hydrostatic equilibrium (i.e., pressure balancing gravity everywhere). AFAIK it is common in astronomy to treat stars this way.

Re: New theory explains how Earth’s inner core remains solid despite extreme heat

#16

Post by egeozcan »

jcoffland wrote: post #14

> The ultimate goal of Earth Sciences is to understand the past, present and future... That is the ultimate goal of all science.

You are right, science is not bound to Earth and also even "the past, present and future" seem too narrow to me. Science is about understanding anything which we are curious about, and that may include alternative timelines which do not lay neither in the "the past, present nor the future" and also the time itself.

Re: New theory explains how Earth’s inner core remains solid despite extreme heat

#17

Post by nonbel »

pdonis wrote: post #12
nonbel wrote: post #2

Something I've been wondering. Does the earth's core have negative heat capacity?[1] I've read that it is usually modeled as a self-gravitating system[2], and that such systems can end up in states with negative heat capacity [3]. [1] > "If the system loses energy, for example by radiating energy away into space, the average kinetic energy actually increases." https://en.wikipedia.org/wiki/Heat_capacity#Negative_heat…

If you look at the Wikipedia article in more detail, you will see that the negative heat capacity of a self-gravitating, isolated system arises from the virial theorem. Heuristically, as a self-gravitating system radiates energy away into space, it becomes more tightly bound; that means it contracts. But as it contracts, the "orbital speeds" of its constituents increase (because decreasing orbital radius means increa…

Interesting, thanks. I still am not sure what the technical meaning of "isolated" is here. But wouldn't such an object continue heating up "infinitely" (maybe stopping at some phase-transition temperature) without constant input of energy?

Re: New theory explains how Earth’s inner core remains solid despite extreme heat

#18

Post by rcthompson »

nickjarboe wrote: post #13
lngnmn wrote: post #3

How do they know that it is solid?)

To the first order it is the fact that a liquid only propagates pressure waves while a solid can propagate shear and pressure waves (which propagate a different speeds).

That's true, but can shear waves be transmitted to the earth's solid core through the liquid iron surrounding it?

Re: New theory explains how Earth’s inner core remains solid despite extreme heat

#19

Post by Florin_Andrei »

rcthompson wrote: post #18
nickjarboe wrote: post #13

Earlier quoted context omitted.

To the first order it is the fact that a liquid only propagates pressure waves while a solid can propagate shear and pressure waves (which propagate a different speeds).

That's true, but can shear waves be transmitted to the earth's solid core through the liquid iron surrounding it?

Pressure waves go through the liquid part, hit the solid part, some of their energy is converted into shear waves which go through the solid core, convert back to pressure waves on the other side, and eventually hit the surface again. By measuring propagation time, direction, etc, the full picture is only compatible with the pressure / shear / pressure double conversion.

TLDR: It's complicated.

Re: New theory explains how Earth’s inner core remains solid despite extreme heat

#20

Post by humanrebar »

jcoffland wrote: post #14

> The ultimate goal of Earth Sciences is to understand the past, present and future... That is the ultimate goal of all science.

Well, it's to use evidence and inductive reasoning to objectively prove that you understand those things.

You can understand lots of things without being able to prove them or explain their underlying mechanisms.

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