<p>I think the answer is 'no', in the sense that 'seismology (i.e., the study of waves propagating within the Earth) tells us the details in a far superior way'. See this paper for an informative treatise: <a href="https://aapt.scitation.org/doi/citedby/10.1119/1.12026" rel="nofollow noreferrer">Brush, S. G. (1980). Discovery of the Earth’s core. <em>American Journal of Physics, 48</em>, 705-724</a>, and these lecture notes <a href="http://www.geo.uu.nl/~berg/geodynamics/lecturenotes.pdf" rel="nofollow noreferrer">http://www.geo.uu.nl/~berg/geodynamics/lecturenotes.pdf</a> on Geodynamics.</p>

<p>Interesting additional tools that you'll find in these works are:</p>

<ol>
<li><p>Figuring out the <strong>mass of the Earth</strong> (using Newton's laws). People found that the average density of the Earth had to be <span class="math-container">$5500$</span> kg/m<span class="math-container">$^3$</span>, while rocks at the surface only had a density of about <span class="math-container">$2700$</span> kg/m<span class="math-container">$^3$</span>, so the interior of the Earth had to be of higher density. Under the assumption that pressure alone cannot be responsible for the increase in density, the high densities had to come from chemical changes such as the presence of metals, particularly because of the Earth's magnetic field. Under the assumption that the pressure <em>was</em> responsible for the high density, the Earth's interior could be gaseous, for example, plain air is more compressible than just rocks, so the Earth's interior could be air (as proposed by Benjamin Franklin in the US!).</p></li>
<li><p>A second clue that the Earth had to have a radially varying density came from the <strong>Earth's moment of inertia</strong> (which was a known quantity, based on astronomical measurements such as the <strong>Earth's axial precession</strong>), which makes it possible to create models that relate density and radius. Of course, with neither quantity well-known, you couldn't do too much with this. But assuming an iron core (with known density, and responsible for the Earth's magnetic field) overlaying a mantle (with density close to that of the Earth's surface), the first radial profiles could be made.</p></li>
<li><p>Models could be made that concerned themselves with the rigidity/deformation of the Earth under forces, such as the response to <strong>ocean tides</strong>, <strong>terrestrial tides</strong> and the <strong>Chandler wobble</strong>. These could be used to even construct some radial profiles of some approximate elastic properties. Only in the 1960s, after seismology was a firmly established technique, people additionally found additional non-seismic evidence of the <strong>Earth's eigenvibrations/free oscillations</strong> where the Earth (as a whole) rings like a bell, which was a very useful independent tool to verify layered profiles of the Earth's elastic properties, and which were important in the discovery of, e.g., the solid inner core.</p></li>
<li><p>The rigidity (from the previous point, and mentioned in the first point) can be linked to densities using (thermodynamical) <strong>equations of state</strong>. Hence, figuring out the appropriate relations between density/pressure/rigidity was of large importance.</p></li>
<li><p>Similarly, with the assumption that the Earth was made with the rest of the solar system, it was possible from the <strong>spectral lines of the sun</strong> and the <strong>chemical makeup of meteorites</strong> to figure out the likely bulk chemical composition of the Earth (<a href="https://en.wikipedia.org/wiki/Chondritic_uniform_reservoir" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Chondritic_uniform_reservoir</a>). If you additionally know the pressure, density and rigidity information, you can make relatively informed guesses about <em>candidate materials</em> that must be present. That is, similar to the answer by a_donda, one must still test how materials really behave in these strange pressure and temperature regimes, which is mostly laboratory work using, e.g., a <strong>Diamond Anvil Cell</strong>.</p></li>
<li><p>Similarly, these lab experiments can tell us that for a given pressure on a given material, what the expected temperatures can be.</p></li>
</ol>

<p>But if you want very solid answers about the 'nature' of the Earth's core, all the most direct answers come straight from seismology. That is the best method to actually constrain the <em>location</em> of the (elastic) properties within the Earth, at a much higher accuracy than any of the other methods can. As secondary consequences, we can use these measurements to make chemical hypotheses about the makeup of the core etc., but those are entirely based on the assumption that the seismic data is correct....so they're not an 'independent' kind of measurement/model!</p>

CC BY-SA 4.0
2020-04-05T14:50:46.207Z
@a_donda All the information comes from the two linked documents which review the material... I must refer you to those if you care about the complete story, these are merely some hints about the full story. You're of course right about the "weight of the Earth"! :-)
Erik
CC BY-SA 4.0
2020-04-10T03:59:03.417Z
While my question turned out to be much more nuanced than I'd expected, this answer best addresses what I was hoping would be explored, so while I can't yet accept any answer as "the right" answer I'll definitely award the bounty. Now I'll go read up on these. Thanks!
uhoh
CC BY-SA 4.0
2020-09-20T22:09:25.210Z
The two references are mostly historical, giving thoughts prior to the space age, radio astronomy, and modern communications. The questions asks whether "there any other measurements that have contributed to current understanding of Earth's core besides these two?" The answer is definitely yes, and extending this to other planets, the answer is a resounding yes.
David Hammen
CC BY-SA 4.0
2020-09-21T07:34:47.680Z
That's fair. Note that I give a whole list of alternatives, before still concluding 'No'...the reason for this is probably that as a seismologist I mostly care about the seismological properties of the core, which are best obtained through seismology! :-) A chemist will care about the chemical make-up. Etc.!
Erik
CC BY-SA 4.0
2020-04-05T07:51:01.407Z
2020-04-05T14:51:02.743Z
2020-04-05T14:51:02.743Z
Erik
<p>The comments to the other question have already alluded to some physical answers that also come out of the lab: One might think that the heaviest elements in primordial Earth should have all sunk into the core by now. But that's not actually the case: For example, uranium with a density 2.5 times that of iron (19.1 vs 7.9 g/cm<sup>3</sup>) has an abundance of about 4 ppm in the mantle, whereas in the core its abundance <a href="https://earthscience.stackexchange.com/questions/4798/what-percent-of-the-earths-core-is-uranium">is believed to be essentially zero</a>. How do we know this? We can make experiments about how easily uranium dissolves in rocky materials vs in iron melts -- and it turns out that if it has a choice, uranium very much prefers to associate itself with rocks and not with iron.</p>

CC BY-SA 4.0
2020-04-03T00:28:41.517Z
2020-04-03T04:03:20.273Z
2020-04-03T04:03:20.273Z
Wolfgang Bangerth
<blockquote>
<p>Are there any other measurements that have contributed to current understanding of Earth's core besides these two?</p>
</blockquote>
<p>The answer is of course &quot;yes&quot;. Other answers have already alluded to laboratory experiments that attempt to re-create conditions similar to those well inside the Earth.</p>
<p>I'll provide two others; there are many more.</p>
<p>One is radio astronomy. Determining the apparent locations of quasars has drastically increased the accuracy of the Earth's orientation. Doing this in conjunction with modern communication techniques results in Very Long Baseline Interferometry. The combination of the two has reduced the uncertainties in the Earth's orientation to well under a milliarcsecond. This gives deep insight (pun intended) into the nature of the Earth's core. The Earth's Chandler wobble does not behave quite like that of a rigid body. How this varies over time gives insights into the nature of the Earth's core. The Earth's <a href="https://www.aanda.org/articles/aa/pdf/2013/07/aa21585-13.pdf" rel="nofollow noreferrer">free core nutation</a> is also observable from the precise Earth orientation parameters.</p>
<p>Another is precise gravity models of the Earth. These too give insights into the Earth's core, including the Earth's moment of inertia, the Chandler wobble, and the free core nutation. Going beyond the Earth, gravity models provide one of the key observational techniques for studying the interior of the Moon, Mars, and Jupiter. Scientists know that the <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103516300720" rel="nofollow noreferrer">Moon</a> and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0032063309000178" rel="nofollow noreferrer">Mars</a> have partially molten cores thanks to gravity models developed from precise orbit determination based on the many satellites that have orbited the Moon and Mars. Scientists know that <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL073160" rel="nofollow noreferrer">Jupiter has a diffuse core</a> thanks to precise orbit determination of the Juno spacecraft's orbit about the planet.</p>

CC BY-SA 4.0
2020-09-21T00:05:13.330Z
This is exactly the dual outcome I was hoping for; 1) to be proven wrong, and 2) to learn something new. It seems I've hit a *jackpot!* I didn't know about any of this. I'll go off and read about these measurements today. *Thanks!*
uhoh
CC BY-SA 4.0
2020-09-20T22:38:47.410Z
2020-09-20T23:23:07.020Z
2020-09-20T23:23:07.020Z
David Hammen
<p>There is much known about Earth's core from painstaking analysis of seismic data, and from detailed magnetic field maps and trends over time.</p>

<p>Are there any other measurements that have contributed to current understanding of Earth's core besides these two?</p>

CC BY-SA 4.0
2020-03-28T13:31:05.773Z
This is a list question, something that's a bit frowned upon across the StackExchange network. I can immediately think of six answers; I'm sure there are more. Those six are very-long-baseline interferometry, satellite radar ranging, inter-satellite ranging, gravity gradient measurements, relative GPS measurements, and precise orbit determination.
David Hammen
CC BY-SA 4.0
2020-03-28T13:34:29.287Z
@DavidHammen the correct answer will be a Boolean + one example if True, not a list. I'm certainly interested to see how one of those gives meaningful information about the Earth's core that goes beyond seismic and magnetic field measurements. So maybe just pick one you like most?
uhoh
CC BY-SA 4.0
2020-03-28T13:49:58.307Z
I'm voting to close this question as off-topic because it is a list question that cannot have an objectively correct answer. Questions such as these are better suited to discussion sites as opposed to Q&A sites (e.g., this site).
David Hammen
CC BY-SA 4.0
2020-03-28T13:52:21.710Z
@DavidHammen The question can be answered with "Yes" or "No". *I wrote it that way intentionally!* You've already stated the answer is "Yes" and need only to support it with an example.
uhoh
CC BY-SA 4.0
2020-03-28T14:44:15.597Z
I'm not a fan of A2A questions; they generally strike me as arrogant / showoff. But I can suggest some better questions that are offshoots of this: (1) How does measuring the Earth's rotation give insights into the Earth's interior? (2) How does measuring a planetary object's static and time varying gravity fields give insight into the planet's interior? (3) What are Love numbers and what do they say about a planet's interior?
David Hammen
CC BY-SA 4.0
2020-03-28T14:49:43.383Z
@DavidHammen A question provides a space for answers. I wonder if the "arrogant / showoff" types you describe more generally post answers exclusively and wouldn't dare to be seen asking questions? Instead of asking for someone to ask the question you'd liked asked so that you can answer it, why not just post the question and the answer together like you did for the [quaternions in Space](https://space.stackexchange.com/q/19369/12102)? That's perfectly fine in SE and much better than just idly complaining that other people didn't ask the question you wanted them to ask.
uhoh
CC BY-SA 4.0
2020-03-30T09:36:15.740Z
See also my answer here: https://earthscience.stackexchange.com/a/18613/18081
Jean-Marie Prival
CC BY-SA 4.0
2020-03-30T11:22:05.440Z
@Jean-MariePrival I see, thanks for the link!
uhoh
CC BY-SA 4.0
2020-04-04T02:33:43.583Z
I've just asked [How do we know the speed of S-waves (shear waves) in the Earth's inner core? Has this been measured?](https://earthscience.stackexchange.com/q/19550/6031)
uhoh
CC BY-SA 4.0
2020-04-05T12:50:14.353Z
@a_donda more on how SE Questions, Answers and Bounties work in [meta.stackexchange.com](https://meta.stackexchange.com/). As for the "outcome", the person who asks the question is always the sole decider what answer (if any) they choose to accept at any time, and there isn't any outcome other than that. Anyone can put a bounty on any question for any of the six following reasons: 1) Authoritative reference needed, 2) Canonical answer required, 3) Current answers are outdated, 4) Draw attention, 5) Improve details, 6)  Reward existing answer, and they can award them the way they like.
uhoh
CC BY-SA 4.0
2020-04-05T12:51:57.200Z
@a_donda this is just how SE is set up. When we post answers, we're done. If the OP decides to accept it, challenge it, up vote it, down vote it, or later un-accept it, that's just what happens and we move on to write further answers. We can of course revise our answers or leave a comment of our own, but we don't tell the OP what to do or not to do.
uhoh
CC BY-SA 4.0
2020-04-05T16:21:58.810Z
@a_donda I don't know what "biasing a question" means. Each SE site has a companion meta site which is used to discuss how the site is used. For Earth Science SE we have [earthscience.meta.stackexchange.com](https://earthscience.meta.stackexchange.com/) If you think there's an issue to be discussed further you could ask a question there, just as one example "Could this bounty tend to bias this question?" This provides an opportunity and space for a discussion much better than a string of comments. Usually one would leave a short comment here letting readers know there's a discussion in meta.
uhoh
<seismology><planetary-science><geomagnetism><core>
Do we know anything about the nature of Earth's core that hasn't come from magnetic or seismic measurements?
uhoh
# Do we know anything about the nature of Earth's core that hasn't come from magnetic or seismic measurements?

(Asked by: username_0 on 2020-03-28)

There is much known about Earth's core from painstaking analysis of seismic data, and from detailed magnetic field maps and trends over time.

Are there any other measurements that have contributed to current understanding of Earth's core besides these two?

**Tags:** seismology, planetary-science, geomagnetism, core

> **Comments:**
> **username_1**: This is a list question, something that's a bit frowned upon across the StackExchange network. I can immediately think of six answers; I'm sure there are more. Those six are very-long-baseline interferometry, satellite radar ranging, inter-satellite ranging, gravity gradient measurements, relative GPS measurements, and precise orbit determination.  
> **username_0**: @username_1 the correct answer will be a Boolean + one example if True, not a list. I'm certainly interested to see how one of those gives meaningful information about the Earth's core that goes beyond seismic and magnetic field measurements. So maybe just pick one you like most?  
> **username_1**: I'm voting to close this question as off-topic because it is a list question that cannot have an objectively correct answer. Questions such as these are better suited to discussion sites as opposed to Q&A sites (e.g., this site).  
> **username_0**: @username_1 The question can be answered with "Yes" or "No". *I wrote it that way intentionally!* You've already stated the answer is "Yes" and need only to support it with an example.  
> **username_1**: I'm not a fan of A2A questions; they generally strike me as arrogant / showoff. But I can suggest some better questions that are offshoots of this: (1) How does measuring the Earth's rotation give insights into the Earth's interior? (2) How does measuring a planetary object's static and time varying gravity fields give insight into the planet's interior? (3) What are Love numbers and what do they say about a planet's interior?  
> **username_0**: @username_1 A question provides a space for answers. I wonder if the "arrogant / showoff" types you describe more generally post answers exclusively and wouldn't dare to be seen asking questions? Instead of asking for someone to ask the question you'd liked asked so that you can answer it, why not just post the question and the answer together like you did for the [quaternions in Space](https://space.stackexchange.com/q/19369/12102)? That's perfectly fine in SE and much better than just idly complaining that other people didn't ask the question you wanted them to ask.  
> **username_2**: See also my answer here: https://earthscience.stackexchange.com/a/18613/18081  
> **username_0**: @username_2 I see, thanks for the link!  
> **username_0**: I've just asked [How do we know the speed of S-waves (shear waves) in the Earth's inner core? Has this been measured?](https://earthscience.stackexchange.com/q/19550/6031)  
> **username_0**: @a_donda more on how SE Questions, Answers and Bounties work in [meta.stackexchange.com](https://meta.stackexchange.com/). As for the "outcome", the person who asks the question is always the sole decider what answer (if any) they choose to accept at any time, and there isn't any outcome other than that. Anyone can put a bounty on any question for any of the six following reasons: 1) Authoritative reference needed, 2) Canonical answer required, 3) Current answers are outdated, 4) Draw attention, 5) Improve details, 6)  Reward existing answer, and they can award them the way they like.  
> **username_0**: @a_donda this is just how SE is set up. When we post answers, we're done. If the OP decides to accept it, challenge it, up vote it, down vote it, or later un-accept it, that's just what happens and we move on to write further answers. We can of course revise our answers or leave a comment of our own, but we don't tell the OP what to do or not to do.  
> **username_0**: @a_donda I don't know what "biasing a question" means. Each SE site has a companion meta site which is used to discuss how the site is used. For Earth Science SE we have [earthscience.meta.stackexchange.com](https://earthscience.meta.stackexchange.com/) If you think there's an issue to be discussed further you could ask a question there, just as one example "Could this bounty tend to bias this question?" This provides an opportunity and space for a discussion much better than a string of comments. Usually one would leave a short comment here letting readers know there's a discussion in meta.  

---

## 3 answers

### Answer by username_1 on 2020-09-20. Score: 3 | Accepted answer

> Are there any other measurements that have contributed to current understanding of Earth's core besides these two?

The answer is of course "yes". Other answers have already alluded to laboratory experiments that attempt to re-create conditions similar to those well inside the Earth.

I'll provide two others; there are many more.

One is radio astronomy. Determining the apparent locations of quasars has drastically increased the accuracy of the Earth's orientation. Doing this in conjunction with modern communication techniques results in Very Long Baseline Interferometry. The combination of the two has reduced the uncertainties in the Earth's orientation to well under a milliarcsecond. This gives deep insight (pun intended) into the nature of the Earth's core. The Earth's Chandler wobble does not behave quite like that of a rigid body. How this varies over time gives insights into the nature of the Earth's core. The Earth's [free core nutation](https://www.aanda.org/articles/aa/pdf/2013/07/aa21585-13.pdf) is also observable from the precise Earth orientation parameters.

Another is precise gravity models of the Earth. These too give insights into the Earth's core, including the Earth's moment of inertia, the Chandler wobble, and the free core nutation. Going beyond the Earth, gravity models provide one of the key observational techniques for studying the interior of the Moon, Mars, and Jupiter. Scientists know that the [Moon](https://www.sciencedirect.com/science/article/abs/pii/S0019103516300720) and [Mars](https://www.sciencedirect.com/science/article/abs/pii/S0032063309000178) have partially molten cores thanks to gravity models developed from precise orbit determination based on the many satellites that have orbited the Moon and Mars. Scientists know that [Jupiter has a diffuse core](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL073160) thanks to precise orbit determination of the Juno spacecraft's orbit about the planet.

> **Comments:**
> **username_0**: This is exactly the dual outcome I was hoping for; 1) to be proven wrong, and 2) to learn something new. It seems I've hit a *jackpot!* I didn't know about any of this. I'll go off and read about these measurements today. *Thanks!*  

---

### Answer by username_3 on 2020-04-05. Score: 3

I think the answer is 'no', in the sense that 'seismology (i.e., the study of waves propagating within the Earth) tells us the details in a far superior way'. See this paper for an informative treatise: [Brush, S. G. (1980). Discovery of the Earth’s core. *American Journal of Physics, 48*, 705-724](https://aapt.scitation.org/doi/citedby/10.1119/1.12026), and these lecture notes <http://www.geo.uu.nl/~berg/geodynamics/lecturenotes.pdf> on Geodynamics.

Interesting additional tools that you'll find in these works are:

1. Figuring out the **mass of the Earth** (using Newton's laws). People found that the average density of the Earth had to be $5500$ kg/m$^3$, while rocks at the surface only had a density of about $2700$ kg/m$^3$, so the interior of the Earth had to be of higher density. Under the assumption that pressure alone cannot be responsible for the increase in density, the high densities had to come from chemical changes such as the presence of metals, particularly because of the Earth's magnetic field. Under the assumption that the pressure *was* responsible for the high density, the Earth's interior could be gaseous, for example, plain air is more compressible than just rocks, so the Earth's interior could be air (as proposed by Benjamin Franklin in the US!).
2. A second clue that the Earth had to have a radially varying density came from the **Earth's moment of inertia** (which was a known quantity, based on astronomical measurements such as the **Earth's axial precession**), which makes it possible to create models that relate density and radius. Of course, with neither quantity well-known, you couldn't do too much with this. But assuming an iron core (with known density, and responsible for the Earth's magnetic field) overlaying a mantle (with density close to that of the Earth's surface), the first radial profiles could be made.
3. Models could be made that concerned themselves with the rigidity/deformation of the Earth under forces, such as the response to **ocean tides**, **terrestrial tides** and the **Chandler wobble**. These could be used to even construct some radial profiles of some approximate elastic properties. Only in the 1960s, after seismology was a firmly established technique, people additionally found additional non-seismic evidence of the **Earth's eigenvibrations/free oscillations** where the Earth (as a whole) rings like a bell, which was a very useful independent tool to verify layered profiles of the Earth's elastic properties, and which were important in the discovery of, e.g., the solid inner core.
4. The rigidity (from the previous point, and mentioned in the first point) can be linked to densities using (thermodynamical) **equations of state**. Hence, figuring out the appropriate relations between density/pressure/rigidity was of large importance.
5. Similarly, with the assumption that the Earth was made with the rest of the solar system, it was possible from the **spectral lines of the sun** and the **chemical makeup of meteorites** to figure out the likely bulk chemical composition of the Earth (<https://en.wikipedia.org/wiki/Chondritic_uniform_reservoir>). If you additionally know the pressure, density and rigidity information, you can make relatively informed guesses about *candidate materials* that must be present. That is, similar to the answer by a\_donda, one must still test how materials really behave in these strange pressure and temperature regimes, which is mostly laboratory work using, e.g., a **Diamond Anvil Cell**.
6. Similarly, these lab experiments can tell us that for a given pressure on a given material, what the expected temperatures can be.

But if you want very solid answers about the 'nature' of the Earth's core, all the most direct answers come straight from seismology. That is the best method to actually constrain the *location* of the (elastic) properties within the Earth, at a much higher accuracy than any of the other methods can. As secondary consequences, we can use these measurements to make chemical hypotheses about the makeup of the core etc., but those are entirely based on the assumption that the seismic data is correct....so they're not an 'independent' kind of measurement/model!

> **Comments:**
> **username_3**: @a_donda All the information comes from the two linked documents which review the material... I must refer you to those if you care about the complete story, these are merely some hints about the full story. You're of course right about the "weight of the Earth"! :-)  
> **username_0**: While my question turned out to be much more nuanced than I'd expected, this answer best addresses what I was hoping would be explored, so while I can't yet accept any answer as "the right" answer I'll definitely award the bounty. Now I'll go read up on these. Thanks!  
> **username_1**: The two references are mostly historical, giving thoughts prior to the space age, radio astronomy, and modern communications. The questions asks whether "there any other measurements that have contributed to current understanding of Earth's core besides these two?" The answer is definitely yes, and extending this to other planets, the answer is a resounding yes.  
> **username_3**: That's fair. Note that I give a whole list of alternatives, before still concluding 'No'...the reason for this is probably that as a seismologist I mostly care about the seismological properties of the core, which are best obtained through seismology! :-) A chemist will care about the chemical make-up. Etc.!  

---

### Answer by username_4 on 2020-04-03. Score: 1

The comments to the other question have already alluded to some physical answers that also come out of the lab: One might think that the heaviest elements in primordial Earth should have all sunk into the core by now. But that's not actually the case: For example, uranium with a density 2.5 times that of iron (19.1 vs 7.9 g/cm3) has an abundance of about 4 ppm in the mantle, whereas in the core its abundance [is believed to be essentially zero](https://earthscience.stackexchange.com/questions/4798/what-percent-of-the-earths-core-is-uranium). How do we know this? We can make experiments about how easily uranium dissolves in rocky materials vs in iron melts -- and it turns out that if it has a choice, uranium very much prefers to associate itself with rocks and not with iron.


---

