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
#2Something 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_ca...
[2] > "The Earth’s outer core is a rotating ellipsoidal shell of compressible, stratified and self-gravitating fluid." https://www.uleth.ca/dspace/handle/10133/3672
[3] > "Negative heat capacities can only occur in isolated or nearly isolated systems. They are impossible in truly extensive systems in canonical ensembles or for that matter in grand canonical ensembles. However, far from being a strange phenomenon only found in the thermodynamics of black holes they occur widely on a macroscopic scale in astrophysics and with less precision on a microscopic scale throughout physics and chemistry. They are the origin of the large fluctuations that occur at phase transitions and we speculate that they cause those transitions." http://adsabs.harvard.edu/full/1977MNRAS.181..405L
Edit: Also, the link to the paper leads to a 404 page... Stabilization of body-centred cubic iron under inner core conditions, Nature Geosciences, nature.com/articles/doi:10.1038/ngeo2892
Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#3How do they know that it is solid?)
Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#4How do they know that it is solid?)
Seismic waves traveling through the earth refract for the same reason that light refracts when entering different substances (e.g. air, water). The inner core has a different density from the outer core, and this difference in density tells us that it is solid. Of course the density difference could be due to something we don't know yet, but this is out current best guess.
Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#5How do they know that it is solid?)
By measuring how quickly seismic waves travel between different points on the earth's surface. Seismic waves travel at different speeds depending on the density and type of material they pass through, which lets us determine the composition of the Earth.
Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#6How do they know that it is solid?)
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Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#7How do they know that it is solid?)
Measuring earthquake wave propagation?
Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#8This 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 and coming to an entirely different conclusion?
Doesn't it seem more appropriate and useful for the scientific community and publishers of these studies to be careful not to state their findings as conclusive and act as if their most recent study does much more than to estimate what might be happening?
Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#9How do they know that it is solid?)
Measuring earthquake wave propagation?
Yes. And to add a missing piece, seismic waves radiate out from the point of vibration. Some of these waves pass through the core of the earth and are received on measurement equipment on the other side. Some of these waves pass through the mantle or the crust. If we know the epicenter of the quake, then we can estimate how long these waves should take to reach our different measuring stations assuming different densities.
Given that we can know how long they actually do take, we can turn around and estimate the mean density along the straight-line path they took. When we determine that the mean density is significantly higher for paths through the center of the earth, that tells us that the material there is much denser, and so we suppose that it could be solid.
Re: New theory explains how Earth’s inner core remains solid despite extreme heat
#10This 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 think the headline is correct, in that the theory explains it. That is, the theory offers an explanation for the phenomenon. It may not, in the end, be the correct explanation, but it's an explanation.
And that's how science advances, with better and better explanations.