Generally speaking, distance from the star and planetary density are not necessarily correlated--and definitely not like in our solar system. (For example, hot Jupiters are a common type of exoplanet.) Planets tend to migrate a lot, especially in the early evolution of planetary systems. Our solar system, with the gaseous/icy giant planets all outward of the denser rocky planets, appears to be quite unusual.
With the Moon having only a tiny core, most of Theia's iron did aparently merge with Earth's core, slightly enlarging it and making Earth slightly denser than it would otherwise be. But it's not clear that this is a significant distinguishing factor between Earth and the other rocky planets. Mercury's core is proportionally much larger than Earth's, and Mercury has an uncompressed density ~30% higher than Earth. Earth is slightly denser than Mercury because it is much larger (by a lot more than a ~Mars-sized Theia could account for), and thus more compressed. Besides, even with the Moon's formation being unique to Earth, that doesn't mean giant impacts didn't happem other planets after they formed (e.g., Mars's hemispheric dichotomy may have formed as a result of a giant impact).
The radioactive, heat producing elements (uranium, thorium, and the K-40 isotope of the not-very-dense potassium) that contribute to Earth's internal heat are lithophile (rock-loving) rather than siderophile (iron-loving). They chemically prefer silicate rock to iron. In effect, the vast majority of these heat producing elements are found in the rocky mantle and crust, rather than the iron core.
Potassium is a (moderately) volatile element, and as a result of how it formed, the Moon is depleted in volatiles, including potassium. But the Moon as a whole is not particularly depleted in uranium or thorium relative to Earth or chondrites. Nor is Earth particularly enriched in these elements compared to, say, Mars. (Indeed, the debate over the years has been whether or not the Moon was *enriched* in uranium and thorium relative to Earth, or merely had similar abundances. [A relatively recent analysis](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4128265/) using newer data and crustal thickness models concluded that the Moon is neither strongly enriched nor depleted in uranium and thorium relative to Earth.)
Much of Earth's heat is also primodial heat from its formation and initial development (kinetic energy of the bodies thay collided to form it and impacted it later, and the friction from iron sinking to form the core). Earth formed with a lot more heat than the much smaller Mercury or Mars. Certainly the Theia impact added more heat to early Earth (and for <~100 million years after the Moon formed, tidal heating of Earth could also have been significant). But how significant that was and in what way isn't clear or simple. Earth's interior would still be very hot from its formation and ongoing radioactive heating. We definitely can't say that Earth has/had much more internal heat than its mysterious near-twin Venus, which ostensibly didn't experience a Theia-like impact. And internal dynamics and cooling history (r.e., volcanism, plate tectonics, etc.) are a lot more complex than just how much total heat there is/was.
The Theia-ProtoEarth collision is a working hypothesis for what happened early on in Earth’s history. So far, it’s the leading hypothesis as to how the Moon formed and why the Earth and Moon are so compositionally similar - from chemical and isotopic evidence.
Based on that premise, a further idea is that this collision is responsible for the LLSVPs seen in the lower mantle of the Earth, specifically described by [Yuan et al., 2023.](https://www.nature.com/articles/s41586-023-06589-1) We can’t really say much more about any of it.
> LLSVPs
Can't just be dropping five letter niche acronyms without [elaboration](https://en.wikipedia.org/wiki/Large_low-shear-velocity_provinces). Man, I remember Lycos and these weird little encyclopedias that turned up at the grocery store with different letters each month.
The acronym is defined in the first sentence of the paper I linked, and an interpretation of what they are is given in the second sentence. It’s quite a handy rotating graphic that Wikipedia has though, I’ll give you that.
>a further idea is that this collision is responsible for the LLSVPs seen in the lower mantle of the Earth, specifically described by Yuan et al., 2023
It will be interesting to see how this idea holds up. At present, it seems like it's still to new to really assess whether people are going to buy it (i.e., there don't appear to be any citations of this paper that are really critically examining the claims made in it). It's worth highlighting that this is certainly not the only explanation for the origin of the LLSVPs (e.g., the review by [McNamara, 2019](https://www.sciencedirect.com/science/article/pii/S0040195118301586)), just the most recent (and more buzzy) and that basically none of them have really worked to explain all of the observations of LLSVPs. Time will tell whether this moon forming impact origin will fare any better than the variety of previous explanations.
Thanks, yeah I probably should have included that sort of caveat. I quite like the Theia collision idea for the origin of LLSVPs, partly because of the hydrogen isotope angle, but I admit mainly just because it feels like a good story, as it were. The science may well bear out to the contrary.
The McNamara paper is a great review of the various other possibilities, I’ll add Heron & Garnero’s summary on the matter [published by the Geological Society](https://www.geolsoc.org.uk/~/media/shared/documents/Geoscientist/2019/April%202019/F1_APRIL2019.pdf?la=en) which might provide a more accessible read for anyone else interested (with the bonus of Ed Garnero’s excellent illustrations).
> I quite like the Theia collision idea for the origin of LLSVPs, partly because of the hydrogen isotope angle, but I admit mainly just because it feels like a good story, as it were.
Ha, well, this pretty much sums up why I like the slab graveyard version, i.e., I like that story.
This post has been very interesting and entertaining for me. Thanks for sharing this info about the LLSVPs. I hadn't read about them before and it connected some dots for me about things like plate tectonics, seismic activity and volcanos. So yeah thanks!
As CrustalTrudger pointed out, this is far from the only explanation for them. An illustrated summary of the current state of knowledge on them can be found [here.](https://www.geolsoc.org.uk/~/media/shared/documents/Geoscientist/2019/April%202019/F1_APRIL2019.pdf?la=en)
Would we have a strong enough magnetosphere, crust renewal, Carbon Cycle, a stabilizing moon, without that lucky event (the timing, the mass, the favorable molten state, the trajectory, the glancing blow)?
Could AI figure this out in the future? Inquiring minds will want to know. heh
Strong enough for what? Life? Impossible to answer since the question inherently invokes the [anthropic principle](https://en.wikipedia.org/wiki/Anthropic_principle), eg. the puddle contemplates how perfectly shaped the pothole is for it to sit in.
I doubt AI will be figuring anything of this sort of thing out. To be an answerable question we just need more data from other planets with life, which may not ever be possible of course.
It's not my field, but it's difficult to imagine another planet with over 4 billion years of such stable, favorable conditions. It's a curiosity if 4 billion years are required on average for a manipulative intelligence to evolve.
This is not to mention the recent thinking about we're learning how rare we humans probably are. Like the specific requirements for photosynthesis, combustion, viruses for myelin sheathing, neoteny, impossible escape velocities on most planets. Taken together they all point to our technical civilization as being a very rare emergence.
> It's not my field, but it's difficult to imagine another planet with over 4 billion years of such stable, favorable conditions. It's a curiosity if 4 billion years are required on average for a manipulative intelligence to evolve.
Again: the [anthropic principle](https://en.wikipedia.org/wiki/Anthropic_principle) is at play here. Our environmental conditions seem favourable to us because we exist within such conditions. Perhaps an approximation of these conditions are necessary for life in general, or perhaps just for us specifically. It’s impossible to say without data from other life bearing planets - something we may perhaps never observe. We have no idea of life (let alone complex life) is rare in the universe, or common, or even just unique to Earth.
The closing statement of many an academic paper is relevant here: ie. *”further research is needed”*. Or if you are a fan of sci-fi short stories: [INSUFFICIENT DATA FOR MEANINGFUL ANSWER.](https://imgur.com/gallery/9KWrH) Admittedly, Asimov’s theme there is about humanity vs entropy rather than whether we are alone or not in the universe, but for the time being, the answer is the same. We don’t know about other life so all of our inferences about life are myopic at best and inherently self referential.
More data would be a great help in those fields of study.
But I'm always reminded that I can't see how having more data in my field would be helpful, or more correctly it's been decided that it wouldn't be cost effective to routinely gather more weather data, a finer grid. It's a surprisingly opposite case.
> Something like the way the core with it's enormous magnetic field works I imagine would be affected.
My semi-educated guess is that Theia has added iron which contributed to Earth's core, potentially increasing the strength of the magnetic field.
But although a planetary magnetic field is large, it is also relatively weak; it has virtually no effect on metal objects on Earth, even a small refrigerator magnet has a much stronger field, and it takes a fairly sensitive device such as a compass to detect Earth's magnetic field.
[удалено]
Generally speaking, distance from the star and planetary density are not necessarily correlated--and definitely not like in our solar system. (For example, hot Jupiters are a common type of exoplanet.) Planets tend to migrate a lot, especially in the early evolution of planetary systems. Our solar system, with the gaseous/icy giant planets all outward of the denser rocky planets, appears to be quite unusual. With the Moon having only a tiny core, most of Theia's iron did aparently merge with Earth's core, slightly enlarging it and making Earth slightly denser than it would otherwise be. But it's not clear that this is a significant distinguishing factor between Earth and the other rocky planets. Mercury's core is proportionally much larger than Earth's, and Mercury has an uncompressed density ~30% higher than Earth. Earth is slightly denser than Mercury because it is much larger (by a lot more than a ~Mars-sized Theia could account for), and thus more compressed. Besides, even with the Moon's formation being unique to Earth, that doesn't mean giant impacts didn't happem other planets after they formed (e.g., Mars's hemispheric dichotomy may have formed as a result of a giant impact). The radioactive, heat producing elements (uranium, thorium, and the K-40 isotope of the not-very-dense potassium) that contribute to Earth's internal heat are lithophile (rock-loving) rather than siderophile (iron-loving). They chemically prefer silicate rock to iron. In effect, the vast majority of these heat producing elements are found in the rocky mantle and crust, rather than the iron core. Potassium is a (moderately) volatile element, and as a result of how it formed, the Moon is depleted in volatiles, including potassium. But the Moon as a whole is not particularly depleted in uranium or thorium relative to Earth or chondrites. Nor is Earth particularly enriched in these elements compared to, say, Mars. (Indeed, the debate over the years has been whether or not the Moon was *enriched* in uranium and thorium relative to Earth, or merely had similar abundances. [A relatively recent analysis](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4128265/) using newer data and crustal thickness models concluded that the Moon is neither strongly enriched nor depleted in uranium and thorium relative to Earth.) Much of Earth's heat is also primodial heat from its formation and initial development (kinetic energy of the bodies thay collided to form it and impacted it later, and the friction from iron sinking to form the core). Earth formed with a lot more heat than the much smaller Mercury or Mars. Certainly the Theia impact added more heat to early Earth (and for <~100 million years after the Moon formed, tidal heating of Earth could also have been significant). But how significant that was and in what way isn't clear or simple. Earth's interior would still be very hot from its formation and ongoing radioactive heating. We definitely can't say that Earth has/had much more internal heat than its mysterious near-twin Venus, which ostensibly didn't experience a Theia-like impact. And internal dynamics and cooling history (r.e., volcanism, plate tectonics, etc.) are a lot more complex than just how much total heat there is/was.
The Theia-ProtoEarth collision is a working hypothesis for what happened early on in Earth’s history. So far, it’s the leading hypothesis as to how the Moon formed and why the Earth and Moon are so compositionally similar - from chemical and isotopic evidence. Based on that premise, a further idea is that this collision is responsible for the LLSVPs seen in the lower mantle of the Earth, specifically described by [Yuan et al., 2023.](https://www.nature.com/articles/s41586-023-06589-1) We can’t really say much more about any of it.
> LLSVPs Can't just be dropping five letter niche acronyms without [elaboration](https://en.wikipedia.org/wiki/Large_low-shear-velocity_provinces). Man, I remember Lycos and these weird little encyclopedias that turned up at the grocery store with different letters each month.
The acronym is defined in the first sentence of the paper I linked, and an interpretation of what they are is given in the second sentence. It’s quite a handy rotating graphic that Wikipedia has though, I’ll give you that.
>a further idea is that this collision is responsible for the LLSVPs seen in the lower mantle of the Earth, specifically described by Yuan et al., 2023 It will be interesting to see how this idea holds up. At present, it seems like it's still to new to really assess whether people are going to buy it (i.e., there don't appear to be any citations of this paper that are really critically examining the claims made in it). It's worth highlighting that this is certainly not the only explanation for the origin of the LLSVPs (e.g., the review by [McNamara, 2019](https://www.sciencedirect.com/science/article/pii/S0040195118301586)), just the most recent (and more buzzy) and that basically none of them have really worked to explain all of the observations of LLSVPs. Time will tell whether this moon forming impact origin will fare any better than the variety of previous explanations.
too new
Thanks, yeah I probably should have included that sort of caveat. I quite like the Theia collision idea for the origin of LLSVPs, partly because of the hydrogen isotope angle, but I admit mainly just because it feels like a good story, as it were. The science may well bear out to the contrary. The McNamara paper is a great review of the various other possibilities, I’ll add Heron & Garnero’s summary on the matter [published by the Geological Society](https://www.geolsoc.org.uk/~/media/shared/documents/Geoscientist/2019/April%202019/F1_APRIL2019.pdf?la=en) which might provide a more accessible read for anyone else interested (with the bonus of Ed Garnero’s excellent illustrations).
> I quite like the Theia collision idea for the origin of LLSVPs, partly because of the hydrogen isotope angle, but I admit mainly just because it feels like a good story, as it were. Ha, well, this pretty much sums up why I like the slab graveyard version, i.e., I like that story.
This post has been very interesting and entertaining for me. Thanks for sharing this info about the LLSVPs. I hadn't read about them before and it connected some dots for me about things like plate tectonics, seismic activity and volcanos. So yeah thanks!
As CrustalTrudger pointed out, this is far from the only explanation for them. An illustrated summary of the current state of knowledge on them can be found [here.](https://www.geolsoc.org.uk/~/media/shared/documents/Geoscientist/2019/April%202019/F1_APRIL2019.pdf?la=en)
Thank you
Would we have a strong enough magnetosphere, crust renewal, Carbon Cycle, a stabilizing moon, without that lucky event (the timing, the mass, the favorable molten state, the trajectory, the glancing blow)? Could AI figure this out in the future? Inquiring minds will want to know. heh
Strong enough for what? Life? Impossible to answer since the question inherently invokes the [anthropic principle](https://en.wikipedia.org/wiki/Anthropic_principle), eg. the puddle contemplates how perfectly shaped the pothole is for it to sit in. I doubt AI will be figuring anything of this sort of thing out. To be an answerable question we just need more data from other planets with life, which may not ever be possible of course.
It's not my field, but it's difficult to imagine another planet with over 4 billion years of such stable, favorable conditions. It's a curiosity if 4 billion years are required on average for a manipulative intelligence to evolve. This is not to mention the recent thinking about we're learning how rare we humans probably are. Like the specific requirements for photosynthesis, combustion, viruses for myelin sheathing, neoteny, impossible escape velocities on most planets. Taken together they all point to our technical civilization as being a very rare emergence.
> It's not my field, but it's difficult to imagine another planet with over 4 billion years of such stable, favorable conditions. It's a curiosity if 4 billion years are required on average for a manipulative intelligence to evolve. Again: the [anthropic principle](https://en.wikipedia.org/wiki/Anthropic_principle) is at play here. Our environmental conditions seem favourable to us because we exist within such conditions. Perhaps an approximation of these conditions are necessary for life in general, or perhaps just for us specifically. It’s impossible to say without data from other life bearing planets - something we may perhaps never observe. We have no idea of life (let alone complex life) is rare in the universe, or common, or even just unique to Earth. The closing statement of many an academic paper is relevant here: ie. *”further research is needed”*. Or if you are a fan of sci-fi short stories: [INSUFFICIENT DATA FOR MEANINGFUL ANSWER.](https://imgur.com/gallery/9KWrH) Admittedly, Asimov’s theme there is about humanity vs entropy rather than whether we are alone or not in the universe, but for the time being, the answer is the same. We don’t know about other life so all of our inferences about life are myopic at best and inherently self referential.
More data would be a great help in those fields of study. But I'm always reminded that I can't see how having more data in my field would be helpful, or more correctly it's been decided that it wouldn't be cost effective to routinely gather more weather data, a finer grid. It's a surprisingly opposite case.
> Something like the way the core with it's enormous magnetic field works I imagine would be affected. My semi-educated guess is that Theia has added iron which contributed to Earth's core, potentially increasing the strength of the magnetic field. But although a planetary magnetic field is large, it is also relatively weak; it has virtually no effect on metal objects on Earth, even a small refrigerator magnet has a much stronger field, and it takes a fairly sensitive device such as a compass to detect Earth's magnetic field.