Belief in Earth's Iron Core still puzzling

[modest]

Originally Posted by CharlieO

Unfortunately, Turtle apparently brags that he will expose and reject anything which indicate a Creationists was asking devious questions [trolling?] in his website. What a bigoted, biased bully. I note he is listed as a “Sponsor.” I also note that no other member has dared to openly criticize Turtle for his hurtful and false assumptions, personal insults and such, albeit you and a few others seem to have wisely counseled that some of my views might be worth considering.

I am a moderator of these forums and I did, in fact, tell Turtle that his questioning of your motives (in particular: assuming they have something to do with creationism) is inappropriate. I'm now also telling you that it is completely inappropriate to call another member a bigot. If you have a problem with a member you can report their post by clicking the red square above it, or you can private message me or any staff member and we will deal with the problem.

I now suggest that we all focus on the science of this topic and avoid any further conversation of an ad hominem nature. Discussing each other's motives and trading insults is just not a beneficial discussion. In that spirit, I'm going to selectively reply to the science portions of your message, Charlie.

Originally Posted by CharlieO

I was taught Earth formed from within a spinning cloud of elements, mainly hydrogen, and, as with any rotating fluid, gaseous or semi-solid mass, the heaviest elements will always be forced outward, leaving the lightest elements in the center.

I think this is the foundation of the problem. You are correct that more massive elements move to the outside of a spinning disc with more force than lighter elements. The force responsible is the centrifugal force which is:

As the mass (m) gets larger, so too does the force (). This means that something with more mass is exerting more outward force when spinning in a circle than something with less mass. An example of this is when you put blood in a centrifuge and it segregates according to density such that the heavier parts throughout the fluid make an aggregate toward the bottom of the test tube.

This cannot happen when the earth formed, and I assure you, Charlie, you will find no textbook saying it can.

In the case of a spinning disc or a centrifuge a mechanical force holds the material to the spinning device. In the case of a forming planet it is gravity which holds materials to the protoplanet. The force of gravity is:

This means the downward force () increases with mass (m). For any given element spinning in the forming protoplanet there are two major forces affecting it: gravity and centrifugal force, and they are both proportional to mass. If the centrifugal force is the greater of the two then the element will be flung away from the forming planet. In that case a planet won't form, so gravity must be the greater force. Since the force of gravity increases with mass, substances with greater density will sink toward the bottom while lighter elements float toward the top.

Gravity must be the major force and it will segregate a fluid by density such that heavier substances move toward the center and lighter elements are pushed toward the exterior.

Originally Posted by CharlieO

Thus, Earth originally having a hydrogen core is what I was taught in the 1950s and then again in the 1970s, albeit seldom clearly stated; usually mentioned as lighter elements.

I don't know much about the gravitational instability models of planet formation of the 50's and 70's. I've just read some of Kuiper's 1951 paper (yes, that Kuiper) advocating that kind of thing. All I can say is that the current favored model is not that of gravitational instability and collapse of hydrogen and helium and it was never really considered seriously for the terrestrial planets. Nonetheless: even where such a model makes some sense (as with Jupiter) it's not in any way unusual for the heavier rock and metal to sink to the core.

Originally Posted by CharlieO

I was also taught that an enormous swarm of iron-rich micro-planets later attacked a smaller proto-Earth in a concentrated bombardment, adding to its mass and making it totally molten. Then, even though early Earth was still spinning to the extent that many believe it was still largely disk shaped, only iron, with some nickel, somehow flowed inward against centrifugal force and displaced the original hydrogen core, vaporizing it and forcing it to vent to the surface where it was blown away by solar winds. Have I got this right?

This is not correct according to modern planet formation models (Solar Nebular Disc Model). Earth never had a hydrogen core. I'll also point out again that "somehow flowed inward against centrifugal force" shows a misunderstanding of physics. No freely self-gravitating collection of material can arrange itself in such a way that lighter elements are attracted with greater force than heavier elements. I think your belief otherwise is the source of many of your disagreements with earth's structure and formation.

Originally Posted by CharlieO

The point I'm making is that such a scenario is physically impossible, largely due to the presence of the Sun and Jupiter's much greater gravitational attraction and the total lack of any similar swarms being evident anywhere in the cosmos, as per recent astronomical observations.

In fact, the gravitational instability scenario where earth starts as a self-collapsing collection of gas is generally considered impossible—as you say. In order for this to happen the collapsing material would need to fight the tidal forces of the sun. The density of the material in the accretion disc would need to be greater than the "Roche density" given by:

where (a) is the distance to the sun. The density needed varies inversely with the cube of the distance to the sun. Given estimates for the mass of the protoplanetary disc, it seems very unlikely that planets as close as earth can form from direct gravitational collapse as you describe above. Even for a planet as far as Jupiter the protoplanetary disc would need to be .3 times the mass of the sun now which is very massive given astronomic observations. It seems unlikely that the gas giants were formed that way and it seems (as you say) physically impossible in the case of earth.

Originally Posted by CharlieO

Do you think the Grand Bombardment is a viable theory as to how Earth's original hydrogen core was replaced by an enormous excess of iron? I don't.

It does not seem possible (as I say above) that earth can ever have had a hydrogen core. There is therefore no need to replace one. Earth's early bombardment has nothing to do with replacing the core.

Originally Posted by CharlieO

Then, I learned later in life that the Grand Bombardment was wrong, albeit taught to hundreds of thousands of students as the primary mainstream geology theory at that time as to how Earth came to have an iron core.

A google search for "grand bombardment" and earth gives 111 results—so, I doubt there is such a thing. The only bombardment I know of is the "early bombardment" revealed by structures on the moon. It took place after earth's formation and has nothing much to do with the content of the core. Do you have a link or reference to a book or publication to that which you're referring?

Originally Posted by CharlieO

Now we are to believe a Mars sized planet, which was largely iron, somehow wandered into Earth's orbit and they collided. They supposedly melted together and the smaller planet's immense, proportionally, iron core was transferred into proto-Earth, again vaporizing Earth's original hydrogen core and forcing it to vent into space and be lost. At least this is how I read the latest reviews of this theory in Winkipedia.

This is not correct. In the theory to which you refer both bodies had iron cores. Essentally, they had equivalent compositions. You should read this:

The Origin of the Moon

Originally Posted by CharlieO

However, there is no mention of how the smaller planet obtained an iron core far greater in proportion to its size than the core which ended up as Earth's iron core in a combined mass.

The proposed impact has been extensively molded. When two objects like mars collide, a great deal of material from the upper layers of each body is left in orbit forming a large moon. Its composition has little iron because the cores of the two impacting bodies mostly does not obtain orbit.

Originally Posted by CharlieO

There is also no mention as to how it was able to wander freely through our solar system, unaffected by the Sun's or Jupiter's gravity. There is also no mention of how it was able to travel in an orbit different from Earth's, even though all the other planets in our solar system travel in the same direction. Thus, I, at least, believe the 'theory' to be good science fiction, albeit physically illogical to the point of being absurd.

Pluto's orbit crosses that of Neptune and there are many solar bodies with eccentric orbits.

Originally Posted by CharlieO

This is my personal opinion, based on the lack of information as to how any Mars sized planet, largely composed of iron, was formed and how it came to be on an opposing orbit to Earth's and how it was able to avoid the gravitational attraction of the Sun and Jupiter; both of which have obviously never experienced any similar event, if their lack of iron is to be considered valid evidence.

It is not suggested to have had an opposing orbit to earth nor to have a composition significantly different from the current combined Earth / moon system. The reason it is a favored theory is because it is the only model which has successfully explained the formation of Earth's moon. It's also very likely that the Sun and Jupiter have both had similar events. You are incorrect about the Sun and Jupiter not having the required iron content. The most current estimates for the total mass of elements in Jupiter other than hydrogen and helium is between 11 and 45 times the mass of Earth. That is certainly enough to account for a couple mars-sized impacts of terrestrial material. As for the sun, it is estimated to have 0.14% iron by mass which is kg. That's 467 times the mass of earth. There's simply no way of saying that planets with iron cores couldn't have plunged into the sun.

I realize you're not meaning to, but all your arguments so far have been against a strawman. I hope you are receptive to their critique.

Originally Posted by CharlieO

Do you think the Earth-Theia collusion scenario is a valid theory as to how Earth acquired its iron core?

I believe it is a valid hypothesis, but is not a theory for how Earth acquired its iron core. It would be more accurate to say "the hypothesis explains why earth's core is as large as it is".

Originally Posted by CharlieO

One forum member suggested Earth might have been “lucky enough” to have condensed from a primordial ring of iron-rich dust. Seems a better theory than both of the above to me, but highly unlikely since nothing like a ring of iron-rich dust has ever been observed. Again, not to say such can't exist.

The best current model of solar and planet formation is the Solar Nebular Disc Model. It explains that planetesimals about 1 kilometer in average size condensed after which the planets accreted from that material.

Originally Posted by CharlieO

It may in fact be a more plausible explanation of how Earth came to have at least some iron in its core. This qualification is made because it has been proven that iron-nickel becomes too dense at core pressures to be the only elements in Earth's core. Therefore, lighter elements are currently being considered for inclusion in Earth's core, which will complicate his explanation; most often mentioned is hydrogen.

No, the most-often mentioned is not hydrogen. It is oxygen and sulfur. Geophysical evidence would be consistent with 5.8 % oxygen and 1.9% sulfur which you can see from the paper I linked yesterday in my post to Moontanman. Notice from a landmark paper in 1952 written by Francis Birch:

The velocities in the core and inner core are also reviewed. The inner core is most simply interpreted as crystalline iron, the outer part as liquid iron, perhaps alloyed with a small fraction of lighter elements. The density and compressibility of iron at high pressures are estimated with the aid of the experimental compressions of the alkali metals...

Elasticity and constitution of the Earth's Interior

So, It has been known for almost 60 years that the outer core is slightly less dense than iron/nickel alone. By the way, there's a quote in that paper which I find funny and you'll like, so I'll quote:

Unwary readers should take warning that ordinary language undergoes modification to a high-pressure form when applied to the interior of the Earth. A few examples of equivalents follow

• Certain = Dubious
• Undoubtedly = Perhaps
• Positive proof = Vague suggestion
• Unanswerable argument = Trivial objection
• Pure iron = Uncertain mixture of all the elements

Originally Posted by CharlieO

In fact, it now appears that hydrogen, compressed at core pressured over time, may become sufficiently dense enough to be near the density required to be Earth's core.

This is false. As Pyrotex has shown, metallic hydrogen has a density of around 1 gram / cm at core pressure (the source of which I quoted in an earlier post). To satisfy earth's total volume and mass it would need to be between 10 and 13.

Originally Posted by CharlieO

IF this proves to be true and that Earth's mantle is heavier than originally calculated, the iron core theory may be in trouble. Heavier mantle equals lighter core, for which iron becomes too dense now.

This would be inconsistent with evidence and well-established physics for a couple reasons. If the core were composed of a lighter liquid than the mantle then the material of the mantle would sink into the core displacing it. The mantle would not be the heavier of the two for very long. Also, seismic data constrains the density of the mantle and core. As the density of the materials change so too does the speed of seismic waves traversing them. Here, for example, are the velocities of p waves:

-source

At about 2890 km the p waves encounter a large increase in density accompanied by a drastic slowing from about 14 to about 8 km/s.

There really is preponderant evidence which agrees with current theories and disagrees with your proposed alternatives.

Originally Posted by CharlieO

Modest: You wrote, “If you consider the leftover ingredients of planet formation which are floating around the solar system; they are stony and iron/nickle (sic) meteoroids.”

Some may consider this to be a fair assumption, but it is based only on the fragments of meteoroids which have survived during their passage through our atmosphere. While there are other types of meteorites, I suspect the original mass of stony meteorites which enters our atmosphere is many fold times greater than the mass which survives and lands on Earth. Whereas, I suspect the original mass of iron/nickel meteorites which survive entry through our atmosphere is not anywhere near as reduced by their passage. Therefore, it seems likely that the iron/nickel found on Earth's surface is only an insignificant portion of the total mass of the alleged “leftovers” floating around the solar system.

I'm not sure what you're trying to say here. My point is that Earth's composition and isotope ratios are remarkably close (near-indistinguishable) from chondritic meteorites. The current favored model of planet formation essentially says Earth is made from these things. They don't have large abundances of hydrogen and helium so it's only natural that Earth doesn't either.

Originally Posted by CharlieO

And, again, I believe the Sun and Jupiter would have attracted the vast majority of these leftovers long ago

Yes, I'm sure they have. The leftover asteroids and meteoroids from the inner solar system and the leftover comets from the outer solar system are often being thrown into the sun, out of the solar system, or bumping into planets. There's still a lot of it out there (NASA is tracking 6,000 asteroids with near earth orbits right now), but the vast majority (even when including the asteroid belt) is certainly gone.

Originally Posted by CharlieO

should they have existed in any useful quantity; yet the Sun and Jupiter show little evidence of acquiring anything near the mass of iron attributed to these alleged “leftovers.”

I already addressed the metalicity of the Sun and Jupiter. I'll add that we watched Shoemaker-Levy 9 hit Jupiter in 1994 and a few weeks ago NASA tracked an SUV-sized asteroid until it hit the earth and they went to Sudan and collected pieces of it and they're studying them now. It is really fascinating what we can learn from these things and it has a lot to do with planet formation.

Originally Posted by CharlieO

Modest: You wrote, “So, we know the composition of these small planetesimals and they are literally the pieces that the earth was made from. Earth and the rest of the inner planets never accreted (sic) hydrogen because it isn't massive enough.”

Accrete means "To grow together, combine; To adhere; to grow (to); to be added". It's a very common word used in astronomy. The planets, for example, formed from an accretion disc surrounding the sun from which they accreted mass.

Originally Posted by CharlieO

Well, I believe this is just an assumption as no one really knows if these small planetesimals are the pieces from which Earth was made. According to NASA observations, suns, planets and moons began as swirling masses in clouds of cosmic dust and gases, evolving into spinning disks and then into solid masses; during which time the heavier elements in every mass, prior to solidification, would be forced outward and lighter elements inward because of centrifugal force. Simple physics. My Cream Separator Theory.

I hope you see the value of bringing these ideas to a science website. In 2007 you presented this idea that the centrifugal force would move heavier elements toward the outside of a forming planet. This notion was immediately corrected by a very qualified physicist in this post. I'll quote him:

Originally Posted by Janus

Where is your evidence that that Earth was spinning so m/ch faster in its youth? (as in enough for the centrifugal effect to become the major factor.)

In order for the centrifugal effect to cause the separation of elements as you suggest (the cream separator effect), it would have to be stronger than the gravity holding the Earth together, in which case the Earth would have never formed in the first place.

The centrifugal effect acts outward from the axis of spin, not from a central point. The separation would happen like the rings of a tree rather than the layers of an onion. Thus you would see all the heavy elements at the equatorial regions of the crust and lighter elements as you approached the poles. We do not.

A few months later you persisted with the notion and I corrected it in this post. Please try to be receptive to the feedback you're getting. Your description of mass separation is not possible. If heavier elements have less inward force than lighter elements then the centrifugal force must be the dominant factor at which point the elements must exceed the escape velocity of the body.

If you are going to continue repeating this claim then you need to provide a scientific source by way of a link or a specific reference to some published media to back it up. This is a site rule at Hypography.

Originally Posted by CharlieO

In fact, NO such planetesimals have ever been observed. This is not to say they don't exist, just never been observed.

By the common definition, asteroids and comets greater than 1 km are planetesimals.

I know this post covers a lot of ground. It might be useful to just focus on just a couple topics. I'm most curious about your reception to heavy elements in Jupiter and your understanding of centrifugal force and gravity as far as floating and sinking materials. If you could explain in depth or find a source for why you think Jupiter can't have a couple earth masses worth or iron or by what physical forces lighter elements can float downward, I think that would be a beneficial area of discussion rather than a carpet response. But, I leave that, of course, up to you.

~modest

[Boerseun]

I think a big obstacle to your understanding is in trying to compare the centrifugal force created by a spinning disc on Earth to what would be experienced in the accretion disc surrounding the infant sun.

A spinning disc on your desk will create centrifugal force, because the reason objects on the disc might be spinning, is because they are physically connected to the disc and are rotating because of that.

An object being part of an accretion disc will not experience centrifugal force, because as far as that particular object is concerned, it will be traveling in a straight line. Every object in an orbit is in a "stable" orbit, i.e. it is following a line that is the resultant of all forces working in on the object.

Another big difference in the image of spinning discs you have in your head and an accretion disc, is that the spinning disc stays static (apart from the rotation) - all the objects on that disc will have the same positional relationship towards all other objects on the disc, regardless of rotational speed. In an accretion disc, following Kepler's laws, objects closer to the centre of the system's mass will orbit faster, and objects further away will orbit slower. Any accretion disc will start to form a spiral as all objects in it find their stable orbits, with objects close to the centre orbiting much faster than those towards the rim. So, it doesn't matter at all what the object is made of, if its velocity is suitable to maintain an orbit around the centre of the system's mass, it will stay right there. If its velocity is any slower than what Kepler would demand given its distance from the centre, it would fall towards the centre. If its velocity is greater, the object will fall away from the centre, towards the rim. This could result in an orbit like a comet's, being highly elliptical, or, given sufficient velocity, it will leave the system altogether.

My point is that the composition of whatever might be orbiting the accretion disk is irrelevant. All that matters, is velocity and distance from the center.

As a matter of fact, the Laws of Gravity and Kepler's Laws have been the same since the disc accreted till today. Which means that Jupiter, having a much lower density than the Earth (demonstrably so) should fall into the sun, and the Earth would fly outwards - if your argument regarding the initial conditions under which they've formed, holds.

Which it clearly does not.

[stereologist]

I was taught Earth formed from within a spinning cloud of elements, mainly hydrogen, and, as with any rotating fluid, gaseous or semi-solid mass, the heaviest elements will always be forced outward, leaving the lightest elements in the center. Thus, Earth originally having a hydrogen core is what I was taught in the 1950s and then again in the 1970s, albeit seldom clearly stated; usually mentioned as lighter elements.

This is not necessarily true. A centrifuge can be used to separate materials in this manner.

On the other hand the oceans have the denser waters at the center of the gyre. The solar system ends up with the denser materials towards the center, not farther out.

I was also taught that an enormous swarm of iron-rich micro-planets later attacked a smaller proto-Earth in a concentrated bombardment, adding to its mass and making it totally molten. Then, even though early Earth was still spinning to the extent that many believe it was still largely disk shaped, only iron, with some nickel, somehow flowed inward against centrifugal force and displaced the original hydrogen core, vaporizing it and forcing it to vent to the surface where it was blown away by solar winds. Have I got this right?

There would not have been an original hydrogen core. To form a hydrogen core large pressures would have been required. The idea that forces would have kept denser materials from flowing towards the center of the earth are wrong.

[maddog]

Originally Posted by CharlieO

To date, two imaginative theories seem to be most popular as explanations for how the theorized enormous excess of iron came to be in Earth's core:

The Grand Bombardment Theory assumes a swarm, consisting of billions and billions (?) of iron-rich planetesimals (micro-planets) bombarded a smaller proto-Earth over a short (?) period of time. These iron-rich planetesimals supposedly added considerable mass and made Earth completely molten through their concentrated impacts within the short (?) period of time. Then, gravity supposedly forced (only) molten iron and nickel into Earth's core, vaporizing the hydrogen originally deposited there when Earth condensed within a spinning mass of dust and gases; largely hydrogen. The vaporized core hydrogen is then assumed to have been blown away by solar winds.

I hope I stated the Bombardment assumption correctly. This is what I was taught in college.

Description fine enough, so far. It is what you do with it.

Originally Posted by CharlieO

However, it seems to me Earth is a relatively insignificant mass in an immense volume of space, orbiting between Sun and Jupiter; whose individual gravitational attractions greatly exceeds that of proportionately minuscule Earth. Therefore, it seems to me the vast majority of iron-rich planetesimals wandering within our galaxy would much more likely have been attracted to either the Sun or Jupiter and largely ignored Earth.

This appears evident in the fact that neither the Sun or Jupiter contain much iron; apparently even less than the cosmic proportion. This fact alone appears to make it impossible for any swarm of planetesimals to have even existed; iron-rich or stony. It also appears to me that it is more likely for a swarm of planetesimals to be only a figment of someone's imagination; fabricated to support a logical assumption which lacks physical proof.
Then we are left with the problem of where did all these billions of planetesmials come from and how were they formed largely of iron. All of which just seems just like more assumptions to prove an assumption to me.

Your conclusion only takes have of the Nebular Hypothesis into account. You neglect all
the asteroids and comets which are numerous in our solar system. Asteroids come in
three varieties: Irons, Stony-Irons, Carbonaceous Chondrites (carbon rich). There are
a lot of Irons in our asteroid belt (as much as 25 % composition). It is from these that
likely pummeled the Early Earth near its beginning to form an iron rich core.

BTW, our sun was formed from a gaseous medium that was rich in iron (Pop II) so our
sun will be rich in iron. So will all the other gaseous (Jovial) planets. Terestrial planets
typically have solid/molten liquid cores depending on mass.

In fact were our planet to have Hydrogen at the core, there were be insufficient pressure
to form Metallic Hydrogen as Pyrotex has already so eloquently explained to you. This means
that no electrical current can flow at the core. Thus no Van Allen Radiation belt. Since
this does exist, you have a contradiction embedded in your assumptions. Earth thus does
have an molten Iron core.

Originally Posted by CharlieO

Does anyone know of a more plausible theory of how Earth developed a core containing such a enormous excess of iron?

Standard model fits fine with all the pertinent results.

Originally Posted by CharlieO

I found the following interesting, especially since no swarms of planetesimals were observed:

Scientific FrontLine / Hubble Observations Confirm that Planets Form from Disks Around Stars

May 3, 2009: Hubble Observations Confirm that Planets Form from Disks Around Stars

More than 200 years ago, the philosopher Emmanuel Kant first proposed that planets are born from disks of dust and gas that swirl around their home stars. Though astronomers have detected more than 200 extrasolar planets and have seen many debris disks around young stars, they have yet to observe a planet and a debris disk around the same star.

Now, NASA's Hubble Space Telescope, in collaboration with ground-based observatories, has at last confirmed what Kant and scientists have long predicted: that planets form from debris disks around stars.

The Hubble observations by a team of astronomers led by G. Fritz Benedict and Barbara E. McArthur of the University of Texas at Austin show for the first time that a planet is aligned with its star's circumstellar disk of dust and gas. The planet, detected in 2000, orbits the nearby Sun-like star Epsilon Eridani, located 10.5 light-years from Earth in the constellation Eridanus. The planet's orbit is inclined 30 degrees to Earth, the same angle at which the star's disk is tilted. The results will appear in the November issue of the Astronomical Journal.

You are just adding more fuel to benefit your opponent's (correct POV).

I f you really wish to think something that is already been resolved for years, then just
subscribe to the Flat Earth Society. They might be still accepting members.

maddog

[Pyrotex]

CharlieO,
thanks ever so much for all the appreciative and flattering things you say about my posts.
But then you turn around and start 'tagging' parts of the theory I presented as being 'lucky' and 'unexplained'. You say no one has ever observed an 'iron-rich ring of dust' around other stars, as if that meant something. Charlie, we CANNOT do spectrometry of dust rings around other stars, YET. The technology doesn't exist, YET. So it doesn't matter.

Get a clue Charlie. If there ever was an accepted theory that the Earth began with a Hydrogen core, it was LONG GONE by the time I was in high school. I'm 62, and our high school science curriculum was one of the best in the state. I read all the excellent science books by Isaac Asimov. No Hydrogen core. My two research papers in my senior year (1965) were on the Birth and Evolution of Stars, and the Formation of Planets. No Hydrogen core.

If there ever WERE a 'Hydrogen core theory' of the Earth, it had already been invalidated by the 1960's, and probably a lot earlier.

Now, it could be that YOUR science teacher(s) in high school or even college were mistaken and gave you some bad information. Sorry about that! I had a biology teacher who swore that Pythons could swallow an adult water buffalo! Wrong! But I went to the encyclopedia and got the facts. Had you gone to the encyclopedia in the 1960's you would have gotten the facts, too: no Hydrogen core.

If you want us to take you seriously, drop all the BS about the 'Hydrogen core theory'.

Let's just take it that you were misinformed, and leave it at that. Iron was a major constituent of all inner-most planets before and during their formation. This has been the mainstream opinion since the 1960's.

[Cold-co]

A MATTER OF GRAVITY

Some two hundred years ago, scientists longed to break free from Church control. To break free, they needed to unseat the Church approved, cold-core cross section that had been taught for over 5000 years. The sleight of hand they devised was so well disguised even the Jesuits, who the Pope directed to derail their efforts, could find no fault in their logic. In time, the Jesuits came to teach the scientist’s view. Today, we perpetuate the scientist’s sleight of hand every time we teach gravitational forces at work within Earth.
Gravity is a bidirectional (elastic) force—Earth pulls you with the same amount of force that you pull the Earth. But since Earth is so much larger than any freely moving body, on or above her surface, we treat her gravity as a directional force. This makes the force of gravity relatively simple, so we teach gravity before we teach elasticity. But in reality, elastic cohesion (the drawing together of particles) is the force identified by Newton in his law of universal gravitation, “Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them.”
In addition to our less than accurate treatment of gravity, seismic wave data show Earth’s upper shells to be solids down to her core. Yet, we treat her as a large liquid drop to calculate her moment of inertia from her rotationally induced flattening (f). Since she is thought to at least act like a liquid, her flattening is believed to be held on check solely by the equatorial acceleration of gravity (ge); hence, our flattening equation becomes f = 1.5(C-A/Ma2) + 0.5 rate of rotation squared times Earth's radius (a)/ge). In so doing, we conclude she has a low moment of inertia. In turn, she must have a molten interior to allow heavier particles to sink deep into her core to achieve the low moment of inertia demanded by our flattening equation. However, our hot-core model is valid only if we ignore horizontal elastic cohesion.
Elastic cohesion in a solid imparts a constant pull between all its parts. But, no one ever bothered to calculate the strength of that pull in Earth’s shells, because in a schematic of forces diagram the improper use of directional forces (the scientist’s sleight of hand) makes them appear to cancel out; but a gravitational pull cannot cancel out another gravitational pull—only balance. Their pulls are still present.
Now, if we treat Earth’s outer shell as a structurally sound, hollow sphere, subject to horizontal elastic cohesion; then the mass movement, created by her rotation, must also overcome that shell’s elastic cohesion before she will flatten. Trigonometric calculations of Earth’s gravitational forces show horizontal cohesion in her outermost shell to be an acceleration of equal value to the acceleration of vertical gravity on her surface, thus our flattening equation needs another component, +0.5 rate of rotation squared times earth's radius/gh. Or, since this acceleration is of equal value to the acceleration of vertical gravity, that vertical equatorial acceleration can be doubled to obtain Earth’s moment of inertia. When doubled, our flattening equation yields a moment of inertia equal to the summation of moments of inertia mathematically derived for the individual shells of a condensed, cold-core model, whose shell densities are proportional to the speeds of seismic waves passed through them. Serendipity!!!
The squeeze afforded by horizontal elastic cohesion, gives us a unique way to look at Earth’s mechanics—one of a contracting pressure vessel driven by an ever increasing packing pressure provided by horizontal cohesion. A pressure vessel capable of producing a natural heat-pumping cycle—like the heat-pumping cycle employed in diamond anvil devices used to determine the physical characteristics of solid hydrogen. Just as the test sample in a diamond anvil gives up heat to move to a denser phase, so too does the hydrogen crystal in Earth’s pressure vessel give up heat—heat that shows up as geothermal energy in or on her surface.

Moderation Note: Subsuquent discussion of Cold-co's model of the Earth's structure has been moved to Cold Core Model of Earth's Structure so that it may be explored without the constraints of this thread's topic.

[CraigD]

The composition and structure of the Earth is an old and profound scientific subject. Science, like philosophy, thrives as a process, the ongoing consideration of a series of “what if”, hypothetical questions. “What if the Earth’s core was mostly hydrogen by mass?” is such a question, and despite it’s having been championed pseudoscientifically by various more and less well known people, some with conventionally religious agendas, some not, deserves sound scientific consideration.

First, it’s necessary to decide what’s meant by the question. “The Earth’s core” is, thanks to years of seismographic experimentation and analysis, well defined: one of two spherical regions centered at the Earth’s center, with radii of about 1200 and 3500 km, or about 1 quarter and 2 thirds of the radius of the Earth. As CharlieO notes, these regions have never been directly sampled – a hole bored down to them and their stuff examined – so their composition can only be decided indirectly.

Next, it’s necessary to decide what’s meant by “mostly hydrogen”. In ordinary conditions, hydrogen is a very low-density (about ) gas. It can be fairly easily liquefied or frozen (at around 20 and 14 K), increasing its density to about 70 (about ). Neither of these densities is nearly sufficient for the Earth’s core, as the Earth’s average density is about (about ).

If the Earth’s core is mostly hydrogen, the hydrogen must be in a very chemically strange state where its nuclei – mostly single protons – are packed more densely than the lowest-energy spacing of their electrons allows in normal atomic matter, a state known as metallic hydrogen, because in this state, it’s electrons conduct electricity – almost certainly superconduct, with zero resistance. Several experiments have produced small quantities of metallic hydrogen, notably the “Nellis experiment” in 1996 and a 2008 experiment by Silvera and Deemyad, which metalized hydrogen at
to Pa at 3000 K
and
to Pa at 1025 to 1055 K
, respectively. In this state, there is practically no limit to how dense hydrogen, or any other fully electron degenerate matter, can be (densities approaching [math]10^{16} \mbox{kg/m}^3, where matter becomes neutron degenerate).

These temperatures and pressures are within the range theoretically predicted for the Earth’s core. So it is, in principle possible for Earth to have a metallic hydrogen core.

An important point needs to be made here: although some hydrogen core proponents emphasize a “cold core”, it’s not necessary for hydrogen to be cold to be a very dense. It is necessary for it to be electron degenerate – a metal – rather than a liquid or ice, where each nucleus retains its electron. Liquid and solid (ice) hydrogen are associated with very low temperatures because, at standard atmospheric pressure, its boiling and melting point are very low (as mentioned above, about 14 and 20 K).

Science, however, can’t stop with finding a hypothesized thing in principle possible. It must provide an explanation for how the thing came to be. Here, our investigation turns from high-pressure chemistry to planetary astrophysics.

From observing stellar systems in earlier stages of development than our own, we know with high certainty that they form from gas and dust clouds, passing through a stage when the young star is surrounded by a protoplanetary disk. Many-bodies computer simulations strongly suggest that these disks accrete into distinct planets of various sizes and compositions. For the same fundamentally mechanical reasons that the average speed of lighter molecules in a gas are greater than that of heavier ones, light elements such as hydrogen, helium, and pretty much all the elements that are gasses at standard pressure and temperature, are the most difficult to accrete, so are accreted in large proportion only by the large accretions that become gas giant planets. Accretions that form smaller planets and other bodies are able to accrete in large proportions only heavy elements, and relatively small amounts of light elements compounded into dense solids, such as H2O ice and, because of oxygen’s strong chemical tendency to compound with heavier elements, various oxygen compounds.

It is because of this fundamental dynamic that “the Earth has a hydrogen core” hypothesis is unlikely. Although there’s was a lot of gaseous hydrogen in the solar system’s protoplanetary disk, it was accreted mostly by the 4 gas giants. The inner planets, and the large moons of the gas giants accreted mostly iron, silicon, and, due to its above mentioned tendency, oxygen.

It’s helpful to compare the composition of the galaxy on average, the solar system, and the Earth. Here’s a table I put together from a variety of sources and approximations:

               Atomic   Abundance by mass                       Abundance Earth
Element        Mass     Galactic     Solar Sys  Earth           /Solar Sys
1  Hydrogen    1.0079   .922927968  .909850951  .000045         .00004945865028
2  Helium      4.0026   .075479649  .088702314  .0000000000045  .00000000005073
8  Oxygen      15.9994  .000818257  .000776145  .301            387.81400488814
6  Carbon      12.0108  .000482111  .000329372  .0000000066     .00002003809870
10 Neon        20.1798  .000083589  .000112182  .000000000004   .00000003565623
7  Nitrogen    14.0067  .000086277  .000102072  .00000068       .00666190637715
12 Magnesium   24.3051  .000030039  .000035024  .139            3968.6652529153
14 Silicon     28.0855  .000029133  .000032611  .151            4630.3188397575
26 Iron        55.8452  .000024569  .000029350  .321            10936.956199868
16 Sulfur      32.0655  .000017273  .000016794  .029            1726.7311303667
18 Argon       39.9481              .000003293  .000000011      .00333968311830
13 Aluminium   26.9815              .000002768  .014            5056.5498760992
20 Calcium     40.0784              .000001992  .015            7528.0760664162
11 Sodium      22.9898              .000001871  .00012          64.106682600422
28 Nickel      58.6934              .000001607  .018            11195.913533258
24 Chromium    51.9962              .000000440  .00000046       1.0448597823342
15 Phosphorus  30.9738              .000000339  .002            5896.9929186927
25 Manganese   54.9380              .000000311  .0000046        14.770269174359
17 Chlorine    35.4532              .000000169  .0000042        24.767370258509
19 Potassium   39.0983              .000000122  .00011          894.71616697406
22 Titanium    47.8671              .000000078  .000029         370.52772172452

In summary, while it’s conceivable that Earth, in its present form, could have a metallic hydrogen core, there’s no scientifically plausible explanation of which I’m aware of how a protoplanetary disk can eventually form such a planet.

[modest]

Originally Posted by craigd

several experiments have produced small quantities of metallic hydrogen, notably the “nellis experiment” in 1996 and a 2008 experiment by silvera and deemyad, which metalized hydrogen at
to pa at 3000 k
and
to pa at 1025 to 1055 k
, respectively. In this state, there is practically no limit to how dense hydrogen, or any other fully electron degenerate matter, can be (densities approaching , where matter becomes neutron degenerate).

These temperatures and pressures are within the range theoretically predicted for the Earth’s core. So it is, in principle possible for Earth to have a metallic hydrogen core.

The pressure in Earth's core cannot be much higher than 300 Gpa. The experiments you reference constrain the possible density of hydrogen at this pressure:

-source

It seems reasonable to preclude the possibility of an hydrogen core by noting that it doesn't have the necessary density at earth's core pressure.

~modest

[Pyrotex]

If I'm reading that chart right, Modest, then the experiments quoted by Craig took place at, say:

150 GPa and 65 GPA

which can be read off the left axis of the chart.
Using the dashed line for shock reverberations, this would give us densities of:

0.7 gm*cm-3 and .53 gm*cm-3

Now, the Earth's core has a density of 5500 kg*m-3

That translates to .55 * 10^6 g*m-3

.......................or .55 * 10^6 * 10^-6 g*cm-3

.......................or .55 g*cm-3

The first density listed above (.7) is indeed higher than .55
and the second one is spot on.

So... why do you say the chart demonstrates that the Earth's core cannot be MH???

[modest]

Originally Posted by Pyrotex

If I'm reading that chart right, Modest, then the experiments quoted by Craig took place at, say:

150 GPa and 65 GPA

which can be read off the left axis of the chart.
Using the dashed line for shock reverberations, this would give us densities of:

0.7 gm*cm-3 and .53 gm*cm-3

Now, the Earth's core has a density of 5500 kg*m-3

That translates to .55 * 10^6 g*m-3

.......................or .55 * 10^6 * 10^-6 g*cm-3

.......................or .55 g*cm-3

The first density listed above (.7) is indeed higher than .55
and the second one is spot on.

So... why do you say the chart demonstrates that the Earth's core cannot be MH???

I believe 5500 kg/m^3 is 5.5 g/cm^3:



You perhaps multiplied by 100 rather than 1000 from kg to g. I do that a lot thinking m -> cm. The inner core is more realistically 12.6 - 13 g/cm^3 while hydrogen at that pressure/temp can't really be above 1 g/cm^3:

What is the best estimate of the densities of the various layers of the Earth?

~modest