Belief in Earth's Iron Core still puzzling

[CharlieO]

While effectively absent for the past year, I've been following threads of interest for some time, unable to participate due to extremely slow dial-up only available to me far out on Colorado's eastern plains and the near constant demands for care-giving. Finally equipped with wireless broadband. Like night and day. Glad to be back.

 

However, it seems the more I learn, the more I discover I don't know or understand. Help is needed.

 

I don't know if Earth has an iron core or a hydrogen core, albeit the latter seems more likely to me; given the constant loss of hydrogen into space which appears to be physical evidence that some sort of hydrogen reservoir exists within Earth. It is the unquestioning belief of many that Earth has an iron core that is puzzling to me.

 

First, I submit the following as a reasonable statement: Currently, temperatures and materials within Earth's core are totally unknown. Exact determination by physical inspection still remains impossible. There are various theories, assumptions and calculations. Some are logical, some illogical, some absurd, but in today's final analysis, it seems to me that no one really knows for sure.

 

As best I can understand from recent research: Earth's magnetic field convinced early theorists that Earth's core was iron, because, at that time, only iron was known to be magnetic. [Hydrogen's magnetic and metallic properties were unknown until recently.]

 

In 1906, seismic analysis determined Earth's core was 16% of its volume and this was estimated to contain 32% of Earth's mass; but only if the core was largely iron.

 

Unfortunately, iron only constitutes 1.1% of all known elements in the cosmos, yet iron is considered to be five times more abundant just within Earth's crust.

 

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.

 

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.

 

More recently, we were offered the Collision Theory, which assumes a smaller proto-Earth collided with an even smaller planet containing a relatively enormous iron core. Then, these planets supposedly melted together and the smaller planet's iron core became Earth's core; while a portion was flung into space and ended up condensing into Earth's moon. How the smaller planet developed an iron core is just as unexplained and this scenario appears equally unlikely; albeit very imaginative.

 

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

 

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.

[arkain101]

My assumption on this matter based off of light research is that our star collected piles of dust and gas from the earlier stages of its life. Some of this dust and gas would likely be elements of heavier properties like iron created from dead and exploded stars.

 

By chance, our lucky star managed to collect a high iron content cloud other gases and dusts. considering the volume of space around the solar system relative to the size of the planets, this cloud must have been extremely dispersed.

 

I could expect that as this mixture of elements orbited the sun they formed into a series of rings, consisting mainly of one type of material. Not much different the look of saturns rings, and the gas separations on saturn and jupiter.

 

The heavier elements formed orbital rings nearer to the sun. Mars and Earth both contain a high level of iron, and it is interesting to note how close their orbital rings are... Which could suggest that this zone around the sun was a high Iron ring.

 

Although I don't know very much on the subject, it seems logical to me that the sun was formed by an entirely different area and cloud of dust...where later, it collected material for planets.

 

Interesting.. I think I will do a some studying in this area.. I don't know much about it myself.

[Boerseun]

Hi there, Charlie - and welcome back.

 

I remember we had this very same discussion last year sometime.

 

And the same answers apply.

 

The Earth does not have a hydrogen core. Density measurements conclusively exclude hydrogen forming the mass of the Earth's core.

 

When the sun ignited, after having condensed from the proto-stellar cloud that made up this solar system of ours, the lightest material got blown outward. That's why you have rocky planets in the interior of the solar system, and gas giants to the outside.

 

Yes, certainly - hydrogen makes up the bulk of our solar system. But the bulk of it is concentrated in the sun, and the gas giants.

 

Judging by the composition of what remnants from the planet-forming days we find on Earth, the leftovers of meteorites and such that are the detritus of our solar system's early days, the bulk of the inner planets are made of iron and nickle. Apart from meteorites, the density of the planet fits in neatly with the proposition that Earth has an iron core. That, also, is ignoring Earth's handy magnetic field, which is also an iron artifact. Or, for that matter, the fact that hydrogen is simply lighter than iron, and will rise, while iron will sink. I can go on, but the fact remains that the Earth's core does not consist of hydrogen.

[Moontanman]

How would you propose hydrogen could migrate to the core? Hydrogen is not a metal unless in it under extreme pressure. metallic hydrogen is not stable, you cannot have a bare piece of metallic hydrogen floating around. There simply isn't a mechanism that would allow Earth to have a hydrogen core. The solar system is a unusual place, the Sun has a higher metal content than most stars. Even Jupiter is thought to have a metal rock core surrounded by liquid metallic hydrogen, not a hydrogen core.

[Turtle]

...

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....

 

Erhm...until recently at any rate. :doh: Baby planet found around star HL Tau - Telegraph

A baby planet has been glimpsed by astronomers in a "womb" of dust and debris around a young star. ...

 

Do we really need to start a new thread on all this? At the very least, let's link to the past discussions. :D :doh:

Consider Hydrogen for Earth's Core

 

Hydrogen escape into space, how much?

[Pyrotex]

Wikipedia -- Earth:

 

Mean radius = 6,371.0 km

Mass = 5.9736 × 10^24 kg

Mean density = 5.5153 g·cm−3

 

Wikepedia -- Iron:

 

Density (near r.t.) = 7.874 g·cm−3

Liquid density at m.p. = 6.98 g·cm−3

 

...at pressures close to those at the center of the Earth (3.2 to 3.4 million atmospheres)..., hydrogen is still not a true alkali metal, because of the non-zero band gap.

 

The density of liquid Hydrogen at 20K is only 0.07 g·cm−3

 

The density of solid Hydrogen, I cannot find (yet), but is unlikely to be greater than 10 times the density of LH2. So, let's assume worst case, and call it 0.7 g·cm−3

 

Allow that about 1/2 (or more) of the Earth's volume is a variety of solid and liquid rocks, like basalt at 3.0 g·cm−3.

To achieve an average density for the whole planet of 5.5 g·cm−3,

the core of the planet needs a density between 7 and 8 g·cm−3

 

The density of Iron (depending on phase and pressure) is between 7 and 8 g·cm−3

 

There is NO CHANCE at all that Hydrogen, in ANY form, at ANY pressure, could be more than 0.7 g·cm−3, and therefore could constitute the bulk of Earth's core. It would have to be at least 10, and probably 20 or 25, TIMES DENSER.

 

NO CHANCE. NO WAY. The Earth's core is not Hydrogen. It is Iron.

 

And NO, we do not need another thread on this very silly, stupid subject. It has all been said before. We've gone over the numbers and the physics until we're numb. Every claim of Core=Hydrogen has been easily and trivially debunked.

[stereologist]

Two other indicators of the contents of the interior of the earth are seismological evidence, and chemical evidence. The crust is deficient in iridium. The element bonds well to iron and has been moved to the core of the earth. An iron core fits with many observations.

 

Some are logical, some illogical, some absurd, but in today's final analysis, it seems to me that no one really knows for sure.

 

When you mention that the universe is 0.1% iron (you wrote 1.1%) you have to realize that is a huge amount since 98% of the universe is hydrogen or helium. Only 2% of the universe is not those 2 elements. So iron is about 5% of everything that is not H or He.

[arkain101]

Take a look at jupiter... Where is the hydrogen located on it?

 

ITS HUGE! and yet, still the gas has not formed a giant molten planet. It has a very thick atmosphere of gases, and to my understanding, the heavier gasses are nearer to the core.

[arkain101]

And NO, we do not need another thread on this very silly, stupid subject. It has all been said before. We've gone over the numbers and the physics until we're numb. Every claim of Core=Hydrogen has been easily and trivially debunked.

 

Hey!! I learned something... stupid subject :(

 

hahah

[modest]

The density of solid Hydrogen, I cannot find (yet), but is unlikely to be greater than 10 times the density of LH2. So, let's assume worst case, and call it 0.7 g·cm−3

 

I think you're spot on—metallic hydrogen between 3 and 4 Mbar looks to be between .45 and 1.3 g/cm^3.

 

 

-

source

 

In 1973, a group of Russian experimenters may have produced metallic hydrogen at a pressure of 2.8 Mbar. At the transition the density changed from 1.08 to 1.3 g/cm^3

 

Hydrogen

 

So, I agree—there doesn't seem to be any way a metallic hydrogen core could contribute the necessary mass to account for earth's total density. :(

 

~modest

[CharlieO]

Let's see. I didn't claim Earth has a hydrogen core in this thread. Some people can sure jump to conclusions or should I say, make assumptions. All I asked was, "Does anyone know of a more plausible theory of how Earth developed a core containing such a enormous excess of iron?"

 

Eaarth's formation in an iron-rich ring of dust and gases is a new one for me. How very convenient. How equally unlikely, but a good attempt and perhaps even possible. At least someone may not be committed to dogmatic assumptions.

 

So many seem to think Earth is a totally unique situation. I, for one, perhaps the only one it seems, thinks Earth was formed by a process that is no different than that of many others, if not all others. Which is why I find the Grand Bombardment theory so stupid, when the gravitational attraction of the Sun and Jupiter is considered. Hard to believe some so-called scientists would even consider 'swarms' of iron-rich micro-planets attacking only Earth in a short (?) period of time and making it molten, while the swarms apparently ignored the Sun and Jupiter.

 

Apparently, the usual assumptions made in amother thread are still being vented, even though I stated I don't know if Earth has a hydrogen core and only asked where did all the iron come from. Puzzling to say the least, considering I was previously assured the basis for this forum is 'social' discussion.

 

Please answer the question, if you can, and save the condemnations for another thread, in which I can't find the time to participate due to my time consuming care-giver duties during the day.

 

Apparently, the fact that no one really knows for sure seems to have hit a nerve. At least I know I don't know everything. I only wanted to know if there were any other theories about Earth being formed with an enormous excess of iron which had some logical sense about them.

 

Well? Where did all the iron come from? Why does the Sun and Jupiter have so little? Simple questions from a simple old car mechanic.

 

Anyone remember the story of the Emperor's new clothes?

[stereologist]

Charlie your comments in this post are a bit weird. Not a flame, condemnation or whatever.

 

Eaarth's formation in an iron-rich ring of dust and gases is a new one for me. How very convenient. How equally unlikely, but a good attempt and perhaps even possible. At least someone may not be committed to dogmatic assumptions.

 

This paragraph for instance appears to be full of uncertainties on your part.

 

Which is why I find the Grand Bombardment theory so stupid, when the gravitational attraction of the Sun and Jupiter is considered. Hard to believe some so-called scientists would even consider 'swarms' of iron-rich micro-planets attacking only Earth in a short (?) period of time and making it molten, while the swarms apparently ignored the Sun and Jupiter.

 

Then you anthropomorphise the situation and ridicule a theory that you hint you don't understand.

 

Apparently, the usual assumptions made in amother thread are still being vented

 

Apparently, the fact that no one really knows for sure seems to have hit a nerve.

 

Next you suggest that you are being treated poorly. I've seen a lot of good information from some knowledgeable sources.

 

From the beginning you did say:

I don't know if Earth has an iron core or a hydrogen core, albeit the latter seems more likely to me;

 

So you sided with hydrogen in the original post and people went to some length to show that hydrogen doesn't work, but iron does.

 

Next your post reviews some material suggesting iron as the core. But you point out that iron is a small amount of the known mass of the universe. After you described a theory you came up with a few paragraphs why this theory does not make sense to you. Then you mention another theory and dismiss that as well.

 

The problem here is that step 1 was to address the claim that hydrogen was more likely the core of the earth. Now you want to go on to step 2 which is to gain a better understanding of theories about the formation of the earth.

[stereologist]

The universe is about 0.1% iron. What about our solar system?

 

The sun and other planets is about 333,000 times the mass of the earth. In addition there are asteroids and comets and whatever. If the solar system is about the same ratios as the universe, then our solar system contains 333 times as much iron as the weight of the earth. Take out the entire mass of Jupiter and that still leaves 15 times the mass of the earth in iron alone. There is plenty of iron around.

 

You mentioned an observation made by Hubble. When you spin a disc where does the heavy material end up? If the sun heats up what does the lighter material go?

 

What about the asteroid belt and the fact that comets are still seen. Does that conflict with your thought expressed here:

Which is why I find the Grand Bombardment theory so stupid, when the gravitational attraction of the Sun and Jupiter is considered. Hard to believe some so-called scientists would even consider 'swarms' of iron-rich micro-planets attacking only Earth in a short (?) period of time and making it molten, while the swarms apparently ignored the Sun and Jupiter.

[arkain101]

CharlieO is wondering. This is a good thing. Lets be kind or be gone.

 

He did ask some good questions, and I believe would learn about the answers for them.

 

1)What are the theories that describe the process for earth attaining an iron rich core, and evidence for them?

 

I don't believe Charlie has dismissed any existing theories as false. Although he has referred to some explanations as stupid, which is fine if that is how he wants to feel about it, but hopefully this is not how he responds to the feedback contributed on this forum. :(

 

 

I interpreted his intentions as being curious, based on the fact he is puzzled.

 

He provided suggestions based on his knowledge, allowing us to get insight into his thinking. And at the same time provided questions to help find information alternative to his thinking, so that he may be rid of this puzzled state.

 

 

Anyway, whether I agree or disagree on how people are treating this topic is besides the point. The puzzling thought of earth obtaining high amounts of iron in a rather low iron content universe. Surely some of the answers must offer up a bit of the fact that this particular solar system was quite rare, one in a million you might say. As for lucky? well that wouldnt be an appropiate word.. It would pose the question of lucky for whom or what, which is a bit off the topic.

 

I have not studied this subject at any great lengths, that is, the formation of planets, and more specifically our own local system. So this is interesting.

 

I probably would not have been inspired (anytime soon, lol) to study it if it wasn't for the questions Charlie has asked, so in that respect I thank him.

 

I see there have been some links provided, and I will be sure to check up on them.

[arkain101]

When you spin a disc where does the heavy material end up?

 

Well, I really don't know how to answer that off the top of my head, because I really don't know what it is asking.

 

As I understand in a gravitationally formed disk, the orbital region is not dependent on the mass. That is, objects can orbit at any region around a gravitational source.

 

What force is "spinning this disk"?

 

Unfortunately I don't follow you here.

[Turtle]

Anyway, we're just not going through all this again. :eek_big: The simple fact is that this earth-core-not-iron bit is all based in Fundamentalist Christian Creationism and at Hypog that doG don't hunt. :dog:

 

12-07-2007 To ALL: If any want to expand their beliefs beyond the popular assumptions regarding Earth's core, there are books and articles by Neil B. Christainson and C. Warren Hunt and others which explain the probability of Earth having a hydrogen core in both greater detail and far better than I. ...

 

Amazon.com: Two Hundred Years Astray: Neil B. Christianson: Books http://www.amazon.com/Hundred-Years-Astray-Neil-Christianson/dp/0962724017#reader

Neil B. Christianson book title: Two Hundred Years Astray: The Epistle To The Creationists

 

Will the staff be so kind as to move this thread to Silly Claims where it belongs?

[Pyrotex]

A few thoughts on CharlieO's other questions about origin of Earth's iron core.

 

There is, indeed, a LOT of iron in our Solar System. Aside from H, He, C, O, Cl, Ar, Si, Na, K, Mg, and possibly a few other elements, iron (Fe) is the most common element around. And it is the MOST COMMON "heavy" element by far. H,He, O, Cl and Ar are gases -- Na, K, and Mg are very light metals, and C and Si are light "transition" elements.

 

Iron is common in the universe because it is the lightest element that is ENDOTHERMIC under Fusion. That means, all other lighter elements can be fused with H or He and RELEASE energy. If you attempt to fuse Fe with H or He, it ABSORBS energy. All elements heavier than Fe are also Endothermic under Fusion. Why do we care? The lighter elements are created in the cores of ordinary stars as they age, until finally they produce iron. If the star is massive enough, the core will become denser and denser as the Fusion fuels become exhausted, and the pressure will force iron to fuse. This absorbs so much energy that the core collapses, triggering a supernova, which blasts all the outer shells of elements (including iron) out into the surrounding space. Look at a picture of the Crab Nebula.

 

This is where all the common elements come from. Including iron.

 

The innermost core of the supernova releases so much energy that the elements heavier than Fe are produced, but only in trace amounts. That's where gold comes from.

 

When a Sun like ours condenses from primordial gas and dust, there will almost always be a residual spin. As it condenses smaller, the spin increases until the star suffers instabilities at its equator. An equatorial ring of matter forms and cools. Compounds containing heavy metals, like iron, or the metals themselves, will be the first to become solids. We know this because a significant portion of meteorites that crash to Earth contain 95% pure iron/nickel alloy. (I have one.)

 

When the Sun-like star finally achieves full Fusion at its core, there is a "fusion-flash" that occurs while the star is achieving equilibrium. This flash heats up and drives off the equatorial ring. But selectively. Solids, being denser, will be slower to heat up, and harder to drive off. The proportion of iron, and indeed, of all solid compounds, many of which contain C and Si, will be highly increased in the region nearest the star, and the lighter stuff, especially H, He, and a portion of the C and Si, will be selectively driven further outward until it, too, can cool enough to form molecules, compounds and dust.

 

So, we have a plausible mechanism whereby the elements and compounds are separated by mass. Very much like a mass spectrometer in a laboratory. Only it's done by the fusion-flash, instead of with a magnetic field. Near the Sun, iron and its compounds can become a significant percentage of all matter -- say 10% to 20%. Far from the Sun, H and He remain the dominant components. In the region in between, you have iron making up only 1% or 2% of the matter and H and He still very significant.

 

This results in a relatively smooth transition of planet types. Iron core planets near the star, H/He gas giants far from the star. Transition planets in between.

 

How do the iron planets form? The secret is water. Water, in both liquid and solid forms, makes for an adequate "glue" to bind small dust particles together. Water in vapor form can absorb to the surfaces of particles, helping to cool the particles, and itself. As more and more particles clump, the average size of dust particles increases. This will occur mostly in a zone around the star where water can be in its liquid state, at least part of the time, under the right conditions -- like in the core of a clump of dust particles.

 

Particles and clumps smash into each other, and break up into finer dust. The finer dust reclumps eventually and smashes again. But this process slowly but surely evens out all the dust orbits, making them almost circular and all in the same plane. By then, some clumps have gotten large enough to hold together by their own gravity.

 

When a clump is large enough, a planetisimal, its gravity gives it a spherical shape. Its core comes under tremendous pressure. This once again acts like a mass spectrometer! And the various compounds at the core again differentiate. Lighter stuff perculates up. Denser stuff sinks down. The core heats up. At temperatures above 2000 F, compounds of iron give up their C, O, H, Si, S and other lighter elements, leaving only elemental iron. Iron is denser stuff. It sinks down.

 

Similar processes are going on in the regions of the gas giants and transition planets. Only those planetisimals not only scoop up dust as they whirl around, they also scoop up the lighter gases, H and He. At first, this is easy because they are still so cold that the gas pressure of even He isn't enough to escape a planet with, say, Earth's gravity. They grow fast, becoming gas giants like Jupiter, with a tiny iron/rock core. By "rock", we mean any substance (not the pure metals) that tends to be a solid at temperatures above the freezing point of water and below, say 1000 F. For example, Silicon Dioxide.

 

By the time the fusion-flash is over, and the sun warms up to its full equilibrium state, most of the gas giants will have enough gravity to hang on to their H and He, even as they warm up a bit.

 

So, that's where all the iron came from. Even though it is only .0001% of all atoms in the universe, there are (at least) two mechanisms or processes around the newly formed star that tended to act as a mass spectrometer, or a mass differentiator, separating out the heavy stuff from the light. Iron in close orbit to the sun tended to stay there after the fusion-flash, whereas the lighter stuff tended to be driven further away. And the cores of planetisimals, if their temperature got high enough, tended to melt and accumulate iron, and drive the lighter stuff upwards towards the surface.

 

The Universe is full of wonderful and totally natural processes that separate, differentiate, purify and accumulate matter. Heads up!