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Icelandic Rocks Suggest Meteorites Brought Gold To Earth

timothy posted about 3 years ago | from the those-are-some-chatty-rocks dept.

Earth 82

sciencehabit writes "Gold, platinum, and other precioius metals were sucked into Earth's molten iron core soon after our planet formed. So where did all of the material for our fancy jewelry come from? According to high-precision measurements of two isotopes, or atomic variants, of tungsten in 4-billion-old rocks from Greenland published online today in Nature [the abstract adds a bit more; the full version is paywalled, though], precious-metal-bearing meteorites struck Earth around this time, coating the planet in a veneer containing gold, platinum, and other elements long after their native counterparts had disappeared into the planet's core."

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More like a "dusting" (4, Informative)

jfengel (409917) | about 3 years ago | (#37344486)

Just a nitpick, but they use the word "veneer" several times in the abstract. It makes it sound like a thin solid sheet of precious metal. That's not what they're trying to imply. They're trying to emphasize the "thinness" of it, but not really getting the "scattered" part.

Probably "dusting" has some specific connotation to geologists. Maybe "scattering" would suit the situation.

Re:More like a "dusting" (1)

Anonymous Coward | about 3 years ago | (#37344694)

You're right that it would have started out as a "dusting" or "scattering", but once you melt the crust and upper mantle, mix it up, and the whole thing starts cooling down and solidifying, it would be more like a "veneer" of comparatively enriched rock (enriched compared to what you would expect). But you're also right that it isn't a thin sheet of metal, we're talking about trace amounts distributed in the rock and which get subsequently concentrated into ore deposits mainly by transporting gold in solution in high temperature and pressure water (hydrothermal systems) and precipitating it somewhere along the way as it travels through fractures in the rock.

Re:More like a "dusting" (0)

wsxyz (543068) | about 3 years ago | (#37345610)

All of the gold, platinum, and other precious metals originally on Earth were sucked into Earth's molten iron core soon after our planet formed...

Now I know where I can find all the gold! CHA-CHING!

Re:More like a "dusting" (0)

Anonymous Coward | about 3 years ago | (#37347332)

You don't find gold in Molten Core, you find Dark Iron. And Ragnaros.

Re:More like a "dusting" (0)

Anonymous Coward | about 3 years ago | (#37349122)

nowadays its pretty useless though, so I wouldn't bother.

Re:More like a "dusting" (1)

bitt3n (941736) | about 3 years ago | (#37351038)

seeing as these are precious metals we're talking about, I would suggest "bedizening."

Green Iceland (0)

Qwrk (760868) | about 3 years ago | (#37344494)

Iceland is very green.
Greenland is full of ice.
And never the twain shall meet, or be mixed up.

Re:Green Iceland -- myth (1)

Rei (128717) | about 3 years ago | (#37346730)

I've seen this so many times recently -- "Ha ha, Greenland is made of ice, and Iceland is made of green grass!" That's such an oversimplification. Iceland has the largest glacier in Europe; just ignoring all of Iceland's other glaciers, that one (Vatnajökull) alone takes up 8% of the country, and is very visible when you approach the country from the south and east (where most settlers would be coming from). And as for the "grass" part that sometimes gets thrown in when describing Iceland, it's not that grassy of a place place at all. Oh, sure, there are ample grassy areas, but there's even more moss, lichen, and plenty of higher plants like blueberries, crowberries, bilberries, etc (and nowadays, lupine). And most of the interior is a barren moonscape. Come winter, the whole island gets snow, although it doesn't stick that well in the southwest (last winter they only had 14 days with snow cover, although it's usually about 3x that).

Greenland is not completely covered in ice; there are some very sizeable areas in the southwest that are green. There are even Greenlandic "forests" (although they're not much to write home about ;) ). Now, yes, there was an element of propaganda in the choice of name for Greenland. But it's not totally off base in terms of the places where people settled.

Re:Green Iceland -- myth (1)

Mindcontrolled (1388007) | about 3 years ago | (#37349040)

Iceland was significantly more green at the time of settlement though - before it got deforested and the consequent erosion of most of the topsoil. The interior always was desert, iirc. A magnificent place, by the way.

Re:Green Iceland -- myth (1)

Rei (128717) | about 3 years ago | (#37351754)

True, over 1/3rd of Iceland used to be forested before human settlement. Well, as much as you can call Icelandic forests "forests" ;) But as you note, the interior was always desert, plus the glaciers were still giant rivers of ice back then, they still got their winter snows, etc. A funny thing, now with the introduction of the lupine/lúpína, some places in Iceland that were never able to be colonized before due to too hostile of a climate, like some of the sands in the northeast, are now being colonized. So in that way, the country is actually getting greener.

Yeah, isn't Iceland such an incredible place? Too good for this Earth. A couple weeks ago I took the time to translate my resume into Icelandic, for obvious purposes. ;) Veistu einhver sem (th)arft** forritara? ;)

** -- Dang Slashdot doesn't let me type thorns :P

Re:Green Iceland (4, Funny)

tehcyder (746570) | about 3 years ago | (#37349688)

Iceland is very green. Greenland is full of ice. And never the twain shall meet, or be mixed up.

I think you need to brush up on your mnemonic-writing skills.

Iceland is greeny while Greenland is icy
The latter is empty, the former's quite pricey..

analogy: (-1)

Anonymous Coward | about 3 years ago | (#37344526)

It's like when I give your mom a pearl necklace.

Gold moves extensively through the crust (5, Informative)

smellsofbikes (890263) | about 3 years ago | (#37344546)

I've read the abstract but it's not clear that they're talking about enormous quantities of added gold/platinum/whatever. One interesting thing about gold, silver, copper, platinum, and some of the other precious metals is that they're soluble in hot water, so what you form is these huge underground plumes of rising hot water, over local hot magma areas, and the plumes are filled with dissolved metals. When the water rises enough it cools and the metals precipitate out -- primarily in cracks through which the water moves, forming veins that contain very high concentrations of precious metals. These plumes can be many, many miles high, and can pull up/concentrate metals from significant depths, so it's not clear to me that early gravity sorting of heavy metals downwards would result in no heavy metals at the surface. (An interesting side-note is that since each metal has a different solubility in water, as the water rises and cools, different metals precipitate out at different points, so if you find silver you're likely to find at least some gold nearby, but most likely not at exactly the same spot.) Note that I'm not a geologist, just an amateur gold hunter, but this is the explanation I've been given by my geologist friends.

Re:Gold moves extensively through the crust (1)

Anonymous Coward | about 3 years ago | (#37344650)

You are quite correct. Best gold reserves are located in or near former vents.

Gold is also precipitated by some bacteria using it as a catalyst to generate energy.

Re:Gold moves extensively through the crust (0)

brian1078 (230523) | about 3 years ago | (#37344736)

I have access to the whole article since I work for a university. But I don't understand anything they are saying. I like your explanation though.

Re:Gold moves extensively through the crust (-1)

interval1066 (668936) | about 3 years ago | (#37344798)

Pretty damned informative post, mod that sucka up.

Re:Gold moves extensively through the crust (2)

Wyatt Earp (1029) | about 3 years ago | (#37344882)

Anyone who knows anything about paleogeology and ore body formation knows that the submitter's article summary is wrong.

Ore bodies formed in a number of different ways and not all of the heavy elements "were sucked into Earth's molten iron core soon after our planet formed."

http://en.wikipedia.org/wiki/Ore#Ore_deposits [wikipedia.org]

While some metals found on the surface probably came from asteroids (Platinum group), that isn't true for the bulk of heavy elements and ore bodies.

Of course all the heavier elements came from the star that was around here before our Sun and solar system formed, but that doesn't mean what we find on the surface all came from meteorites and asteroids after the planet's formation.

Re:Gold moves extensively through the crust (2)

Rei (128717) | about 3 years ago | (#37346810)

Not to mention that asteroids can cause sizeable ore deposits without bearing the ore themselves. A good example is the Creighton nickel/copper/platinum-group metal deposit under Sudbury, Ontario. The area was struck by a huge asteroid 1.85B years ago, which blasted out a large chunk of the crust. The huge transient crater (250km across -- contrast with 170km for Chicxulub) then became filled with a mantle melt plume, yielding large amounts of heavier metals close to the surface.

Re:Gold moves extensively through the crust (2)

tehcyder (746570) | about 3 years ago | (#37349850)

Of course all the heavier elements came from the star that was around here before our Sun and solar system formed, but that doesn't mean what we find on the surface all came from meteorites and asteroids after the planet's formation.

So what you're saying is that we are stardust, we are golden?

Re:Gold moves extensively through the crust (0)

Anonymous Coward | about 3 years ago | (#37344910)

They are talking of almost ALL the gold, platinum and platinoid metals currently in the crust. The problem with those present in the material first accreted is not that they are heavy at all, it is that they are siderophile, very much so. Which means that they love being in iron, compared to being in silicates. So when, after accretion has progressed enough, iron is segregated to form the core, and it will bring his friends with him. Nickel of course, but also gold, platinum, etc.

Re:Gold moves extensively through the crust (2)

MatthiasF (1853064) | about 3 years ago | (#37344964)

Add on the fact the gold itself could be elevating the boiling point of the water when both are already highly pressurized and you'll discover why marble is such a pretty rock!

Re:Gold moves extensively through the crust (0)

Anonymous Coward | about 3 years ago | (#37345010)

My understanding was that the elements that were sucked down to the core by gravity were really sucked down to the core.

And that the plumes you're talking about would not be ejecting material from that far into the Earth, and would only be pushing stuff from the upper mantle.

But, I could be wrong. I'm only speculating after reading a couple of paragraphs.

Re:Gold moves extensively through the crust (3, Interesting)

ElectricTurtle (1171201) | about 3 years ago | (#37345102)

Superplumes are believed by some to emanate from the core itself, though potentially spawning a chain of other plumes at different strata. It's not really a settled matter in the geological sciences.

Re:Gold moves extensively through the crust (4, Informative)

RockDoctor (15477) | about 3 years ago | (#37350224)

I've read the abstract too, but having been reading Moorbath et al's work for years, studying the chemical evolution of the mantle, I've got a better idea what they're talking about.

Your comments about the non-zero solubility of [anything] in hot water are not incorrect, but not relevant to this work.

The LHB veneer idea doesn't claim that there would be no siderophile elements at the Earth's surface after segregation of the core. It simply states that the early mantle and the early segregating core would have been in (approximate) chemical equilibrium, and consequently the concentrations of different elements in the iron-rich phase compared to the silicate-rich phase would have approximated towards the concentrations predicted from the partition coefficients of the relevant species in the relevant conditions. (This is a tautology - that is what "partition coefficient" means ; whether the conditions approached equilibrium is a more moot point, but they would probably have satisfied my Mantle Petrology tutor's criteria of being to more than 100km depth for more than 100 million years, which is a regime not terribly amenable to experiment.)

However, when one does the sums, and plugs in the experimental data that one has, one finds that there is, in most mantle samples from 3+ billion years ago and 100+km below the surface, more of various elements, including tungsten, gold, PGEs, etc., which should have been taken core-wards with the differentiation of the planet. So, either the segregation process and the rates of diffusion were less efficient than we have reason to believe, or there is something peculiar going on.

It gets more peculiar though ... some sources of samples (diamonds, to be precise) do show mantle materials that have been depleted in siderophile elements to the expected extent (compared to meteorite materials).

So in some places the process works as expected, and in others, it doesn't. Which is damned peculiar. And that peculiarity is what makes them come up with the model of late accretion of a modest amount of (undepleted chondritic) material onto the upper surface of the mantle after the accumulation of 90%+ of the Earth and the segregation of the core.

That puts it into the time scale appropriate for the (probable) Moon-forming Giant Impact, and for the considerably later "Late Heavy Bombardment", but I've not yet seen anyone explicitly linking the 3 events into two or even one event.

Memo to self : must make time to attend the next public lecture I hear of being given by Moorbath; this is a dead-interesting topic.

NO SILLY MAN !! GOD DID !! (-1)

Anonymous Coward | about 3 years ago | (#37344676)

You obviously have never been to Kansas !! It's God's Country !! All the rest of you are going straight to HELL !!

4 billion years? (-1)

Anonymous Coward | about 3 years ago | (#37344732)

That's impossible, we all know the earth is only about six to seven thousand years old. It's obvious that gold, platinum and other precious metals are all lies fabricated by the devil.

It's all at the core? (0)

Anonymous Coward | about 3 years ago | (#37344806)

"Gold, platinum, and other precioius metals were sucked into Earth's molten iron core soon after our planet formed."

Forget lottery tickets I'm buying a shovel!

Re:It's all at the core? (0)

lpp (115405) | about 3 years ago | (#37344874)

Best bring a nice portable A/C unit. Here ya go... got a good sturdy one to sell ya right here. Cash only. No refunds.

Depends on your interpretation... (0)

Anonymous Coward | about 3 years ago | (#37344864)

For me the songs of Pláhnetan, Bellatrix, Trúbrot etc suggest many things, but I've never considered them as offering any insight into the metalurgical make up of the earths crust. Maybe it's a specific niche of Icelandic Rock?

This is ridiculous. (3, Insightful)

ElectricTurtle (1171201) | about 3 years ago | (#37344962)

While I'm sure that some precious metals have arrived from space after the earth's accretion, I think it's rather a stretch to think that the concentration in places like South Dakota or Alaska/Yukon are the result of impact events.

It's true that these elements settled into lower strata, but it must also be remembered that many volcanic events are fueled by plumes of material that emanate from the core itself (the Yellowstone Caldera is believed to be such). That certain metals were concentrated in the lower strata during Earth's early formation does not mean that 100% of them stayed there.

Re:This is ridiculous. (1)

demonbug (309515) | about 3 years ago | (#37345318)

While I'm sure that some precious metals have arrived from space after the earth's accretion, I think it's rather a stretch to think that the concentration in places like South Dakota or Alaska/Yukon are the result of impact events.

It's true that these elements settled into lower strata, but it must also be remembered that many volcanic events are fueled by plumes of material that emanate from the core itself (the Yellowstone Caldera is believed to be such). That certain metals were concentrated in the lower strata during Earth's early formation does not mean that 100% of them stayed there.

I think there is a slight misunderstanding here. Even the so-called mantle "superplumes" only originate at the core-mantle boundary; it is not generally considered (afaik) that they actually involve any significant amount of core material. The density difference between the liquid outer core and the lower mantle is too great for significant amounts of the core to join an upwelling through the less-dense mantle, even if significantly hotter. These plumes are generally considered to be made up of mantle material that is greatly heated (through direct contact with/close proximity to the core) and which forms a large plume rising through the mantle.

Re:This is ridiculous. (1)

ElectricTurtle (1171201) | about 3 years ago | (#37345754)

There are two things being neglected in that, a) scale and b) the difference between (relatively) recent geological events and those that would have occurred in the immediate aftermath of the formation of a stable crust.

As significant as large regional veins of precious metals' ore are to mining operations, if one hypothesizes that they were originally brought to the outer crust by superplume-driven volcanic events that would make Krakatoa look like a science fair display they would account for a very, very minute percentage of the total material being moved by the eruption. So if only a small amount of material actually leaves the core during plume events, that doesn't invalidate the hypothesis on its face.

Something also to be borne in mind is that these sorts of events tend to happen over and over again in (relatively) the same place (you can see the drift in the hotspot responsible for Yellowstone Caldera is only a few hundred miles, which becomes closer and closer the farther down you go by the very nature of spheroids). So if some core material is only partially transited during the first event, it might be moved further by the second and further by the third etc.

Quite frankly it makes me want to dig up my old rock hounding pick and go prospecting around some of these mega calderas.

Re:This is ridiculous. (0)

Anonymous Coward | about 3 years ago | (#37347288)

All heavy metals were created only one way, by Supernova, that is it.

http://www.gemologistsam.net/did-gold-come-from-a-supernova/#more-487

So it may have been here in the original formation, but good odds
a lot of it showed during the heavy impact period long before
humans walked the planet.

Re:This is ridiculous. (1)

hesaigo999ca (786966) | about 3 years ago | (#37354504)

I would like to also point out that at any time magma can touch these formations deep within the core through shifts in the tectonic plates, thereby completely melting any deposit of precious ore. Where does this magma bring these materials in liquid form, probably where most people are really thinking of,
such as the upper depths and not the lower ones......or the lower ones...bringing them to the next shifted region.....etc....

I also think at some point if a crater was created by a striking meteor, containing some materials described here....it would be possible that such said metals could also be liquified and displaced from the original area should the meteor have struck during a time or location where the crust was thin and not well formed.

Meteorites (1)

Anonymous Coward | about 3 years ago | (#37344988)

'Meteorites' brought everything to Earth.

Re:Meteorites (0)

Anonymous Coward | about 3 years ago | (#37345544)

Amen!

Re:Meteorites (0)

Anonymous Coward | about 3 years ago | (#37349458)

But not all at once, of course.

Iceland isn't the star of the paper (4, Informative)

Anonymous Coward | about 3 years ago | (#37345012)

Iceland != Greenland.

In fact, it wouldn't make a speck of sense if it was Iceland being studied, because Iceland is a geologically very young volcanic island with rocks no more than ~40 million years old, whereas the rocks being studied in this paper are 4 billion years or so and among the oldest on Earth. The whole point of the paper is to show that tungsten isotopes have changed over Earth history, and that the change happened quite early. They do compare the old Greenland tungsten isotopic measurements to more recent igneous rocks such as the ones from Iceland, but you could have as easily mentioned Hawaii, the Azores, the Canary Islands, and several other "recent" locations used for the comparison. Iceland isn't special in that respect.

The premise of this paper is that the difference can be explained if the early Earth (>4 billion or so) chemically differentiated initially and most of the siderophile elements (things like tungsten, gold, platinum, etc.) sank to the core during that process, leaving the surface rocks more depleted. That's the time the Greenland samples may represent. Then at a younger time, speculated to be near the ~3.8 billion year late heavy bombardment [wikipedia.org] , a bunch more meteoritic stuff was dumped on the top (more siderophile-enriched), mixed into the upper part of the mantle, and igneous rocks have been generated mainly from that upper mantle source ever since (including the more modern samples they are comparing to, and also the ~2 billion-year-old samples they also show). There are other scenarios, but it is plausible and ties in with other evidence about the late heavy bombardment (such as Nd isotopic data from Sm/Nd and Hf/W dating). They model the effects of some alternative models and show those models can't easily be used to explain what is seen. It's a pretty testable hypothesis as people continue to do tungsten isotope studies on rocks of a variety of ages before and after the late heavy bombardment. This is a pretty bold paper.

Re:Iceland isn't the star of the paper (1)

anorlunda (311253) | about 3 years ago | (#37345550)

I don't understand. Why should tungsten isotopic abundances change over time on Earth as compared to in space?

Is is because the core has become enriched in heavier elements and that tungsten isotopes are formed as fission products of a depleted crust?

Re:Iceland isn't the star of the paper (3, Informative)

Anonymous Coward | about 3 years ago | (#37347378)

"I don't understand. Why should tungsten isotopic abundances change over time on Earth as compared to in space?"

Do you *really* want me to try to explain that? :-) Well, hey, this is slashdot. People here aren't stupid and I'm up for a challenge, although I'm not an expert on this stuff either.

Okay, first of all there are several isotopes of tungsten (W). The ones relevant in this paper are 182W and 184W. These are both stable, non-radioactive isotopes, but the 182W is also produced by the decay of radioactive 182Hf -- that is, over time the amount of 182Hf in a batch of solar system stuff (like the entire Earth) is going to decline due to decay, and the product is 182W. Thus, the amount of 182W is going to correspondingly increase, causing the 182W/184W ratio to climb. Wherever the 182Hf is present you'll get changing tungsten isotopes in that batch of material -- shifting the tungsten ratios over time from whatever it was initially. Wherever the 182Hf is chemically depleted from rocks or their melts, the 182W/184W ratio remains static (because you're not adding any new 182W from the decay process). So, in a way you have a tungsten isotopic system that will indicate the presence of 182Hf even if the 182Hf has eventually decayed away entirely. If Hf was ever there, the W ratios will be perturbed.

Got that so far?

Another important point: 182Hf has a half-life of "only" 9 million years. After about 10 half lives (i.e. ~90 million years), the amount left will fall into the range of measurement uncertainties and effectively can be treated as zero, and in practice the limit is usually less than that (turns out to be ~60 million for the Hf-W system). Even 60 million years is darn short compared to the multi-billion-year age of the Earth. How much 182Hf should be left in the Earth? None. The only way to change the 182W/184W ratio after that is to mix batches of stuff that have different 182W/184W ratios together.

Ok, now we start making planetary bodies. Take a batch of material that got blown out of a supernova somewhere, swept up due to gravity, and eventually start accreting into the sun, planets, and other bits. It starts off with a certain amount of 182Hf which starts decaying, and with a particular 182W/184W ratio. Everything is happily tracking along together until you start chemically separating things, and in this case Hf and W have very different chemical behaviors in typical solar system materials and conditions. Specifically, Hf tends to go with "lithophile" elements -- that is silicate rocks and melts. By contrast, tungsten tends to go with the "siderophile" elements -- i.e. common metals such as iron and nickel. In small meteorites that didn't glom together into bodies hundreds of km in diameter, chemical differentiation never really happens because they didn't melt. They've been "frozen" since the time the solar system formed. In those the Hf decays, alters the W isotopes, and pretty much reflects the mix of Hf and W in the original, average material that formed the solar system. We can sample this by analyzing the meteorites for their W isotopes, but you have to be sure it is the undifferentiated ones (generally speaking, these are the carbonaceous chondrites [wikipedia.org] ). There is a lot of diversity to meteorites.

Meanwhile, in the larger bodies, like big asteroids (think Vesta size), moons, or planets, the stuff starts melting. The metals start sinking to the cores due to their density, taking the W with them. Very little Hf goes along. At the same time, the silicates separate/float into the upper portions, taking most of the Hf. This doesn't happen instantly, but the bottom line is, you end up with silicate materials enriched in Hf compared to the undifferentiated meteorites, and a core that is depleted in Hf compared to the undifferentiated meteorites. Therefore, you would expect silicate rocks in differentiated bodies to have their W ratios strongly perturbed compared to those meteorites. They will have more 182W from the decay of 182Hf, and higher 182W/184W ratios. The core (if you could get a piece) would have a lower 182W/184W ratio. This is where it gets really interesting, because the chemical differentiation process is not instantaneous. If it happens quickly compared to the rate of 182Hf decay, the W ratios will be perturbed a lot (plenty of 182Hf left). If it happens slowly, it won't be perturbed much (because the Hf will decay away before the batches of material separate). "Quickly" versus "slowly" is essentially on that ~60 million year timeframe previously mentioned. With the right numbers for the chemical segregation of Hf versus W in melts, the right volumes of material, etc., you can mathematically model what the various scenarios should be (use the calculus, Luke). But keeping it simple, this means that if chemical segregation happened over longer than ~60 million years then you shouldn't see much difference in W isotopes between undifferentiated meteorites versus silicate rocks on the Earth. We *do* see a difference, implying that chemical segregation of the metal of the core was completed fairly quickly after accretion, in under 60 million years or so.

If your background isn't in geochemistry and you managed to follow all that, I'm impressed.

Finally, getting to your specific question. The short answer is, these W isotopic abundances haven't changed much in the last few billion years because the 182Hf is long gone. What you are seeing is relict bits from the time when they *were* changing because 182 Hf was still around, and as different batches of material were separating and, *potentially* still being added to the Earth from meteorites (but you would need *plenty* to affect the volume of material already here). The latter is what this paper is about: that the values for ~4Ga (billion year) rocks are measurably different from the W values measured now. That's odd, because the changes should be largely done by that point. One of the challenges addressed in this paper is getting the measurements precise enough to be convinced the difference is real -- to shrink the error bars. That's why they talk about "quintuple" measurements and averaging measurements. The difference is quite small, but it is enough to suggest one possible explanation is the arrival of a late batch of accreted material (the "late heavy bombardment [wikipedia.org] ", specifically, at about 3.8-3.9Ga) to perturb the system. This would be meteoritic material that still retains the original, average W isotopic ratios for the solar system, and thus mixing that into the formerly Hf-enriched mantle and crust of the Earth would shift the values. Over time, things would get mixed more deeply, slightly shifting them further to today's values.

For your second question, yes, you do have the right idea, except that it isn't fission that produces 182W from 182Hf, just normal radioactive decay.

When you tie all this to other isotopic systems with different decay rates and chemistry (e.g., Sm/Nd), you can get some pretty amazing clues to what was going on in the early solar system, but it is all very technical stuff.

If you want to read the details of how the 182Hf/182W system can be used to unravel early events on the Earth and in the solar system, I recommend this other paper in Nature [nature.com] , but you'll need a subscription to read it. This paper by Kleine [ucsc.edu] [PDF] is even more technical, but it is a really nice review of how these systems are used for a variety of meteorites, the Earth-Moon system, and even Mars.

I have to be honest. I'm not sure I got it all right, but hopefully that made sense.

Re:Iceland isn't the star of the paper (1)

anorlunda (311253) | about 3 years ago | (#37349884)

Wow! Thanks for your substantial effort to educate me. I think I do follow what you wrote.

The key point is that you say HF and W behave different chemically. I was of the impression that isotopes of the same element always behave alike chemically.

Re:Iceland isn't the star of the paper (0)

Anonymous Coward | about 3 years ago | (#37350052)

Objects in space are bombarded with high energy particles that don't make it to the earth'c surface, maintaining a baseline concentration of isotopes. Once on the surface, the half-life depletion process becomes dominant. Of course, certain ratios of stable elements are also important for analysis such as Iridium.

Re:Iceland isn't the star of the paper (0)

Anonymous Coward | about 3 years ago | (#37363350)

Iceland != Greenland

Correct, but the pedant in me would like to point out that Greenland is an island of Iceland (despite being much bigger), therefore rocks from Greenland are still Icelandic.

Icelandic Rock... (0)

Anonymous Coward | about 3 years ago | (#37345046)

Icelandic rocks should quit 'suggesting' things and start providing evidence and facts! :) Who taught rocks to talk anyway? I know there isn't much to do there...

Interesting Proposition, But I Don't Buy It (4, Informative)

Winchestershire (1495475) | about 3 years ago | (#37345126)

My degree is in geology; while I have no problem with the idea that some of the deposits came from asteroids and the like, there are far too many other ways that many of these deposits can be formed here on earth. I know that for precious metals like gold and silver, hydro-thermal deposits are quite common sources of these ores (with a large number of these being found in or around granite sources.)

Re:Interesting Proposition, But I Don't Buy It (1)

demonbug (309515) | about 3 years ago | (#37345898)

My degree is in geology; while I have no problem with the idea that some of the deposits came from asteroids and the like, there are far too many other ways that many of these deposits can be formed here on earth. I know that for precious metals like gold and silver, hydro-thermal deposits are quite common sources of these ores (with a large number of these being found in or around granite sources.)

The question isn't really about where the deposits near the surface come from; these are almost always the product of circulation of water/rock through the crust and upper mantle, as you suggest. The question is why these very dense minerals are available in the upper mantle/crust to be deposited in the first place. Going by density alone, one would expect that the same processes that resulted in an iron/nickel core during early stages of the formation of the Earth would result in the majority of precious metals also being incorporated into the core - after all, the specific gravity of iron and nickel are only ~7.5-8.5, while gold and platinum are ~18-21. The fact that this isn't the case could be explained if the gold/silver/etc. we see in deposits near the surface (and the parent source scattered throughout the crust and upper mantle) is the result of enrichment from meteor impacts after the differentiation/stratification of the Earth into core/mantle/crust.

Of course, iron and nickel are widely available near the surface too, so I'm not sure that a mystery really exists here - obviously there could be some precious metals incorporated into the core, and some that remained near the surface by being parts of melts of sufficiently low density or being bonded to oxygen or sulfur or other low-density elements.

Re:Interesting Proposition, But I Don't Buy It (1)

Winchestershire (1495475) | about 3 years ago | (#37347044)

Well there is always the hypothesized possibility of mantle plumes carrying/moving heavier materials to the surface (thru volcanism at or near the surface).

Dang Son! (1)

LWATCDR (28044) | about 3 years ago | (#37347786)

There be gold in that there core! Stake a claim and start a digging! Yea Haw we're gonna strick it rich.

Re:Interesting Proposition, But I Don't Buy It (0)

Anonymous Coward | about 3 years ago | (#37346126)

As a geologist, could you comment on the possibility that the gold and silver formed in hydrothermal deposits may have originated from that dissolved in sea water?

Another thing: since there are significant deposits of iron ore in the crust, it seems very likely that the "iron catastrophe" did not cause all the iron to melt to the center of the Earth. In fact I find it hard to imagine any realistic model that would not leave a significant fraction of iron in each of the layers above the core, maybe just a few percent, but that is still an awful lot of iron. Any comment on that would be appreciated as well.

Re:Interesting Proposition, But I Don't Buy It (0)

Anonymous Coward | about 3 years ago | (#37348362)

Ocean water is pulled into the mantle mainly via subduction. I don't know enough about geochemistry (give me a few weeks) to tell you how much gold/silver dissolve in water, but precious metal deposits probably has more to do with sulfide precipitation within the crust than bulk deposits concentrating from sea water. Sea water doesn't really get "filtered" or something as it returns to the surface.

The iron catastrophe was simply the stratification of elements within the forming planet. Just as sand does not sink to the bottom of your beach pail instantly, neither does the iron that was evenly distributed in the molten ball of rock orbiting the sun 4.6Ga. Not all the iron was able to sink to the core of the planet. Iron combines chemically with a lot of things, and can form solid solutions that are less dense than pure Iron thus it doesn't all sink. Finally, mantle plumes can bring iron-rich minerals back to the surface via normal convection and other processes.

Indeed (4, Funny)

Darth Hubris (26923) | about 3 years ago | (#37345174)

'Icelandic Rock' was ABBA's greatest rival in the late 70's. They did indeed bring much gold [wikipedia.org] to earth.

Re:Indeed (0)

Anonymous Coward | about 3 years ago | (#37345224)

ABBA was a Swedish band.

Re:Indeed (1)

93 Escort Wagon (326346) | about 3 years ago | (#37345344)

ABBA was a Swedish band.

Read...the...parent...comment....again....slowly.

Re:Indeed (1)

Bucc5062 (856482) | about 3 years ago | (#37351092)

dammnit, suckered by a quest for knowledge...and a well hidden trap indeed. For some reason my brain just had to know what icelandic rock band was a rival to ABBA so I clicked...fool of a Took.

However, Google saved me. I don't think these bands [wikimedia.org] matched the star power of ABBA, but now I know Icelandic Rock is real.

Re:Indeed (0)

Anonymous Coward | about 3 years ago | (#37349654)

'Icelandic Rock' was ABBA's greatest rival in the late 70's. They did indeed bring much gold [wikipedia.org] to earth.

According to John Stewart [youtube.com] , it was the rock from California towns that turned into gold. Someone needs to get their history correct.

And that's why Bitcoins are so valuable (0)

turkeyfeathers (843622) | about 3 years ago | (#37345390)

Gold, silver and platinum are scattered all over the earth waiting to be found, and each new find drives down the price of that commodity. Bitcoins, on the other hand, exist only in the Earth's molten interior and in a fixed quantity and are therefore more valuable than the "so-called" precious metals (not to mention the euro and the dollar).

Re:And that's why Bitcoins are so valuable (1)

blair1q (305137) | about 3 years ago | (#37345730)

The Chinese are preparing a mission to an asteroid to bring it back to mine it for Bitcoins.

Much of the recoverable gold is in recent geology (0)

Anonymous Coward | about 3 years ago | (#37345478)

http://en.wikipedia.org/wiki/Gold_in_California

Scientists believe that over a span of at least 400 million years, gold that had been widely dispersed in the Earth’s crust became more concentrated by geologic actions into the gold-bearing regions of California. Only gold that is concentrated can be economically recovered. Some 400 million years ago, California lay at the bottom of a large sea; underwater volcanoes deposited lava and minerals (including gold) onto the sea floor; sometimes enough that islands were created.[1] Between 400 million and 200 million years ago, geologic movement forced the sea floor and these volcanic islands and deposits eastwards, colliding with the North American continent, which was moving westwards.[2]

Beginning about 200 million years ago, tectonic pressure forced the sea floor beneath the American continental mass.[3] As it sank, or subducted, beneath today's California, the sea floor heated and melted into very large molten masses (magma). Being lighter and hotter than the ancient continental crust above it, this magma forced its way upward, cooling as it rose[4] to become the granite rock found throughout the Sierra Nevada and other mountains in California today — such as the sheer rock walls and domes of Yosemite Valley.[5] As the hot magma cooled, solidified, and came in contact with water, minerals with similar melting temperatures tended to concentrate themselves together.[5] As it solidified, gold became concentrated within the magma, and during this cooling process, veins of gold formed within fields of quartz[4] because of the similar melting temperatures of both.[6]

Did meteors do everything? (1)

Sebastopol (189276) | about 3 years ago | (#37345700)

It sounds like any time geologists can't figure something out, the answer is "meteors". From life, to water, to now gold and silver, the refrain is "meteors". Kinda starting to sound a bit repetitive over the past decade, or is it just me? I am obviously not a geologist.

Re:Did meteors do everything? (0)

Anonymous Coward | about 3 years ago | (#37347090)

How did the Earth form? As dust that eventually clumped and accreted, while other clumps were forming and bumping in to it to eventually build the entire planet. So the whole damned place was formed by meteorites.

So lets just go Pluto and drop the planet moniker altogether -- we're just a great big meteor with fungus on it.

What boggles my mind is... (2)

Dr. Spork (142693) | about 3 years ago | (#37345776)

How did that Icelandic rock (mentioned in title) get to Greenland (summary)? Is the submitter perhaps afflicted with geographasia americana, whose symptoms include thinking that distinct countries/provinces are the same thing?

Obvious answer (1)

rossdee (243626) | about 3 years ago | (#37345982)

Vikings carried it there.

Or it could have been a swallow

(Erik the Viking was written by the same people that wrote Monty Python)

Re:Obvious answer (0)

Anonymous Coward | about 3 years ago | (#37350996)

Or it could have been a swallow

An African or European swallow?

To the Moon! (1)

Commontwist (2452418) | about 3 years ago | (#37345866)

Forget Earth--go to the Moon or Mars for getting the goodies closer to or at the core. Sure, both still have molten gooey centers but we can get a lot closer to the center than here on Earth. After all, if one says meteorites brought metals to Earth the same deal applies to the Moon especially since it used to be part of Earth. (No doubt stirring the pot when that happened...)

Heck, digging deep enough to get heat and power from the core would make it much less likely for a stray meteorite to wipe out your living area. Decompression would also be unlikely given all the doors from there to the surface. Only problem would be gravity and possible moon quakes as water and air would be unlikely to escape.

"4-billion-old rocks" (2)

tqk (413719) | about 3 years ago | (#37345962)

FTS:

... precious-metal-bearing meteorites struck Earth around this time, coating the planet in a veneer containing gold, platinum, and other elements long after their native counterparts had disappeared into the planet's core."

Correct me if I'm wrong (I'm sure you will), but isn't the present theory of the origin of the Earth that it was formed by meteoritic bombardment? Where would these so-called "native counterparts" have come from except from said meteors? This summary suggests all the glittery stuff came from the stragglers of the same event.

Isn't the Earth considered to be about 4 billion years old? In other words, WTF is the summary suggesting (besides a monumental lack of reading comprehension)?!?

What are "4-billion-old rocks" [sic].

[I won't bother to mention the Greenland/Iceland confusion as others are carrying that torch well already.]

A collective faceplant rang out like a thunderclap as all the under-employed geeks wondered how people like that get and retain employment.

Re:"4-billion-old rocks" (2)

tqk (413719) | about 3 years ago | (#37346286)

Here's an idea. Maybe /. editors should run their stuff by the other /. editors before unleashing their stuff upon the general readership. Consider it something like a code review, or quality assurance, or basic best practice.

Or, is this a cleverly devised feature of /. to pump up comments? If so, I don't think clever really comes into it.

What meteorites? From where? Let's get some (1)

Anti Cheat (1749344) | about 3 years ago | (#37346172)

Well then, if a significant amount of gold came from meteorite bombardment. Then doesn't it hold that our local asteroid fields should have vast amounts of the stuff? Shouldn't a spectral scan of the sky hint at all this?

Let's go get some.

Re:What meteorites? From where? Let's get some (1)

ElectricTurtle (1171201) | about 3 years ago | (#37347174)

I don't think you realize how expensive it is to leave the gravity well. Even if there were solid gold bullion in orbit there would have to be a fuckton of it just for the operation to break even.

Mining in space will be important, but it's unlikely to be important or cost effective to get the materials back to Earth. Whatever is ultimately mined in space will likely stay in space to build things there.

Re:What meteorites? From where? Let's get some (1)

Hierarch (466609) | about 3 years ago | (#37348316)

Mining in space will be important, but it's unlikely to be important or cost effective to get the materials back to Earth. Whatever is ultimately mined in space will likely stay in space to build things there.

Not so. It's easy to get things back to Earth once you get out there. Sure, it's very expensive to get there, but so long as you're prepared to stay for a long time you can amortize over the mission.

The delta-V you'd need to hit a 3-5 years delivery window from the asteroid belt to Earth would be pretty small. There's a small matter of the delivery being, shall we say, postage due. Bit of an, er, impact on the wallet. Not to mention the neighborhood. But it would get there!

Re:What meteorites? From where? Let's get some (1)

PPH (736903) | about 3 years ago | (#37347618)

That seems logical. The earth and the other rocky planets' native heavy metals sank to their respective cores during formation. The asteroid belt being either the result of the breakup of a planet or its failure to form would consist of deposits of these materials randomly distributed throughout the belt.

Core is liquid, so... (1)

gstrickler (920733) | about 3 years ago | (#37347310)

the denser metals such as Cu, Pt, Ni, Ag, and Au should have started to stratify over 4B years. Therefore, what we need is a really big straw, about 4000mi/6400km long to stick into the earth's core and pump out all the those valuable metals. The straw will probably need to be made of graphite and/or carbon nanotubes to handle the heat. On the plus side, it may be a diamond when we remove it.

Think of the side benefits. We can pump iron and transuranic wastes in to replace what we're drawing out. The transuranic wastes will help keep the core hot, and they should stay there for a long time. So, we get valuable metals and we get rid of some nuclear waste at the same time.

So, where do I apply for a grant to start research and drilling?

Re:Core is liquid, so... (1)

spauldo (118058) | about 3 years ago | (#37348118)

Rock acts differently under the kinds of pressures you get when you get close to the mantle.

From what I understand, it can flow to some degree, even in solid form. Thus, your well keeps trying to collapse while you're drilling. Also, with the high pressures come high temperatures, and it's difficult to drill in high temperature situations (this is what shut down the Kola Borehole in Russia).

Drilling is also really expensive, and it gets more so the deeper you go. You need special (read: expensive) materials to withstand the forces involved.

There have been a few government financed scientific deep drilling projects. No one has yet to get close to the mantle.

Re:Core is liquid, so... (0)

Anonymous Coward | about 3 years ago | (#37349782)

Yes. Maximum depth drilled so far is about 11km at the Kola borehole you mention. If the Earth were the size of a peach, we haven't even drilled through the skin yet. Oh, and the space station orbits in the fuzz. To reach the core you'd have to drill a hole almost 3000km long, and long before you got there it would be closing up behind you.

People have a poor appreciation for scale.

Re:Core is liquid, so... (1)

gstrickler (920733) | about 3 years ago | (#37352238)

I guess you missed the "really big straw". The whole thing was satire.

Re:Core is liquid, so... (1)

spauldo (118058) | about 3 years ago | (#37360020)

"Really big straw" is a fair description of deep well drilling, and there are a lot of (uninformed) people who think drilling into the mantle can be done using current generation technology. The government has assigned grants for projects that would lay the groundwork for your straw.

So while your post may have been satirical, it wasn't really all that farfetched.

Re:Core is liquid, so... (1)

gstrickler (920733) | about 3 years ago | (#37360634)

I'm familiar with DSDP, ODP, IODP, and Kola. And yes, drilling into rock at 180c-300c requires some engineering. But we have cutting tools that handle much higher temperatures than that. The bottom line is that we've drilled only a little deeper (about 900m) than the Challenger Deep in the Mariani Trench, the lowest known place on earth. Kola only made it about 1/3 of the estimated distance through the crust.

And then we need a really big straw.

Lotus Eaters (1)

RoccamOccam (953524) | about 3 years ago | (#37348232)

"Element 79" by Fred Hoyle
So what would happen if a large meteorite of pure gold landed in, say, England?

That is why (0)

Anonymous Coward | about 3 years ago | (#37348788)

American's are Gold diggers, There be gold in them there hills!

The 5th Elephant Theory... (0)

Anonymous Coward | about 3 years ago | (#37349214)

So Terry Pratchett was bang on the money again?

The Fifth Elephant [wikipedia.org] :-)

Duhh.. (0)

Anonymous Coward | about 3 years ago | (#37350908)

It says in the Quran 57:25 , http://quran.com/57/25
More explanation on the verse. http://www.harunyahya.com/miracles_of_the_quran_p1_04.php#10

Aliens helped.. (1)

raymorphic (2461142) | about 3 years ago | (#37417298)

Can we have some more gold?
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