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View Diary: BREAKING: Meteor airburst over Chelyabinsk (318 comments)

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  •  Every piece of precious metal jewelry you own (11+ / 0-)

    comes from a meteorite.  Gold, silver, platinum - all these metals that were present when the Earth formed sank to the core because of their density.  We only have access to them from more recent asteroid impacts that have yet to be subducted into the mantle.  In fact, every computer chip on Earth has asteroid material in it.  We're communicating with each other right this moment through asteroid bits.

    Pour yourself into the future.

    by Troubadour on Fri Feb 15, 2013 at 12:18:44 AM PST

    [ Parent ]

    •  So lava has no metal content in it at all then? (3+ / 0-)
      Recommended by:
      Onomastic, Aunt Pat, Troubadour

      Because that's basically what you're asserting by claiming that new crust formed by bringing the mantle back up to the surface again in volcanic activity at the plate boundaries isn't a source of metal - that once it melts into the mantle that's it it never comes back up again and instead you have to wait for more meteorites.

      •  Lighter metals like aluminum stick around. (2+ / 0-)
        Recommended by:
        ivorybill, Aunt Pat

        They just recirculate in the upper layers.  But gold, platinum, etc. sink to the core over the long term and have to be replenished externally.  That's why they occur in veins rather than being evenly distributed - they were delivered by asteroid impacts.

        Pour yourself into the future.

        by Troubadour on Fri Feb 15, 2013 at 02:05:10 AM PST

        [ Parent ]

        •  I find myself agreeing with (6+ / 0-)

          all the other science-related comments you are making in this diary, but I do wonder about this one... gold often occurs associated with quartz in very slow-cooling igneous deposits. Some gold, I suppose, may be deposited in hydrothermic veins by superheated water or gas - but gold is so inert and the melting point is so high, I can't imagine surface deposits of gold from meteorites would impact that process much.  

          A lot of gold also comes from secondary deposition in sedimentary deposits - but isn't that usually gold that eroded out of igneous deposits in the first place, and then was redeposited in sedimentary deposits?

          “If the misery of the poor be caused not by the laws of nature, but by our institutions, great is our sin.” Charles Darwin

          by ivorybill on Fri Feb 15, 2013 at 02:45:36 AM PST

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          •  I don't have detailed knowledge. (1+ / 0-)
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            But just to be clear, I'm not saying it was all deposited here recently - just all of it was more recent than the formation of the planet, and depends on how old the crust is.  Earth was essentially a viscous fluid in its early history - so prior to the formation of continents, and thus platforms to maintain these metals once deposited from outside, there was just no way for them to remain on the surface or even in the mantle.  I'm not a geologist, so I have to defer to anyone with actual training, but this is how I've learned it from a planetary science perspective.

            One anecdotal fact that that sheds some light on this: South Africa.  Huge precious metals mining industry.  Some of the oldest crust on Earth, going back to the very first theorized continent to emerge from the molten surface, Vaalbara (3.6 billion years old).  And it's because of that fact - that the crust has not been recycled - that it has accumulated so much of that material.  Whereas you go to places like Hawaii where the land is being actively created from lava, and it's pretty far from being a metallic wonderland.  Often we find these "strikes" in mountainous areas not because the mountain-building caused them, but because very old crust migrated over time and eventually was uplifted in such a way that the metal was exposed.

            I hope that helps.

            Pour yourself into the future.

            by Troubadour on Fri Feb 15, 2013 at 03:33:06 AM PST

            [ Parent ]

          •  gold veins like the quartz fields of CA (10+ / 0-)

            are always produced by geothermal activity.  

            The phrase that all gold comes from asteroids is only correct in the sense that all metals were formed in the fusion of an exploding star.

            If the earth formed suddenly and at once, heavy metals would sink to the core, but in the slow and violent accretion process of earth's formation, the core was disrupted throwing heavy metals up and allowing them to solidify at the crust.  

            Since earth was our familiar size, gold in veins have been present on earth, and were not the result of secondary impact events.

            •  I'm sorry, that's just not correct. (0+ / 0-)

              Earth didn't have a permanent crust until nearly a billion years after its formation.  Unless you're a geologist, I have to disagree with your characterization.

              Pour yourself into the future.

              by Troubadour on Fri Feb 15, 2013 at 12:23:58 PM PST

              [ Parent ]

              •  What say we cite some references? (1+ / 0-)
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                Others have simply gotten old. I prefer to think I've been tempered by time.

                by Just Bob on Fri Feb 15, 2013 at 02:04:57 PM PST

                [ Parent ]

                •  If I understand the article correctly (0+ / 0-)

                  the Nat Geo source supports what I'm saying - that the gold deposits moved over time with ancient crust into mountains and were only then exposed and washed away by streams.  In other words, not gushed up in lava or hydrothermal processes.  Also, they're talking about South Africa, which has some of the oldest crust on Earth, which is why it has so many precious metals in it - they haven't been subducted.

                  Pour yourself into the future.

                  by Troubadour on Fri Feb 15, 2013 at 05:55:47 PM PST

                  [ Parent ]

                  •  One of those articles cited a modified (0+ / 0-)

                    placer theory...a combination of both.

                    Of course in one sense you are absolutely right. We are all star dust. That's all there is for both us and the planet.

                    Others have simply gotten old. I prefer to think I've been tempered by time.

                    by Just Bob on Fri Feb 15, 2013 at 06:00:04 PM PST

                    [ Parent ]

                    •  Right, but I don't just mean "in a sense." (0+ / 0-)

                      I'm saying that there is no physical geological process I'm aware of - as a scientifically literate semi-layman - that would prevent any significant quantity of primordial gold, platinum, etc. from sinking into the core over billions of years of tectonic convection.  South Africa is rife with these metals because it's among the oldest crust on the planet and has been absorbing impacts for 3.6 billion years.  

                      Humbler deposits - e.g., the California Gold Rush - were caused when older crust migrated into younger, more geologically active areas and got warped into hills and mountains where erosion could expose the metals.  But you go to the youngest crust on Earth, you simply will not find gold and platinum.  That's why Polynesian culture didn't have all the precious metal jewelry of cultures like the Inca, Hittites, or Upper Egyptians.

                      Pour yourself into the future.

                      by Troubadour on Fri Feb 15, 2013 at 06:08:45 PM PST

                      [ Parent ]

                      •  We have to properly define the question (1+ / 0-)
                        Recommended by:

                        We know the earth doesn't create gold (to any significant degree[1]) and platinum, so the question is how is it that some areas have more than others. There is a hydrothermal explanation and even the placer theory relies on water transport from areas of concentration.

                        I guess it might be interesting to consider how gold would be concentrated in asteroids to a degree that impacts would create enriched concentrations on earth. A greater age for the gold than the surrounding material doesn't address the question of transport and deposit.

                        The question has been argued for over a hundred years, and while we have more knowledge, there still is no clear answer.


                        Right. The bacteria doesn't create gold. It only concentrates it. I still thought it was interesting and provides another possible means of concentration and transport.


                        Others have simply gotten old. I prefer to think I've been tempered by time.

                        by Just Bob on Fri Feb 15, 2013 at 06:28:44 PM PST

                        [ Parent ]

                        •  The answer lies in asteroid formation itself. (1+ / 0-)
                          Recommended by:
                          Just Bob

                          Asteroids (except for the handful of largest, like Ceres and Vesta) don't have enough gravity to have differentiated interiors - i.e., the different elements don't separate out, and there's no erosive process that would evenly distribute them either, so they occur in heterogeneous blobs throughout the interior.  Not blobs of one pure substance, obviously, but highly enriched ones.  When they impact, lighter material is mostly blasted away while the heavier material is mostly deposited.  

                          Over time the crust where the impact occurred moves and fragments, and once parts of it get uplifted into mountains, the continental crust is eroded and exposes the veins of precious metal.  This also means pieces of it can wash downstream, but as the history of any gold rush will tell you, finding gold in a river means the main strike is somewhere up in the mountains closer to the river's source.  It's not that there's more gold to be found in mountains than flat land - it's just where the material is more likely to have been exposed by erosive processes.

                          So that's why these metals occur in heterogeneous blobs on Earth: Because they occur in heterogeneous blobs in the asteroids that deliver them.

                          Pour yourself into the future.

                          by Troubadour on Fri Feb 15, 2013 at 06:41:10 PM PST

                          [ Parent ]

                          •  More meteorites strike the oceans than on land (1+ / 0-)
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                            Of course any fragments are buried under miles of ocean sediment and isolated from chemical reactions and transport other than upthrusts.

                            There are sea shells found on Sandia Crest at an elevation of 10,700 feet. That implies exposure to weathering, transport, and concentration. Of course that area has also had huge lava flows from time to time.


                            It seems that each of the Southwestern states has an apparent geologic specialty. If so, and Arizona is the big Canyon state, Utah is the Mesozoic fauna state, and Colorado is the big snow-capped Rocky Mountains state, then what is New Mexico? New Mexicans need only look out their windows for the answer: New Mexico is the Volcano state. New Mexico has one of the greatest concentrations of young, well-exposed, and uneroded volcanoes on the continent. And as a bonus, it is also the Rift Valley state; it has one of only four or five big continental rifts in the world, East Africa being one of the other ones. The fact is, New Mexico is one of the best places to study the natural history of volcanoes. Twenty percent of the U.S. National Parks and Monuments based on volcanic themes are in New Mexico. There are more here than Arizona, Idaho, Oregon, and Washington combined.

                            Volcanism in New Mexico is not "extinct," but is dormant. The record of volcanism in New Mexico is continuous over tens of millions of years, and there is no reason to think it stopped magically 3000 years ago with the eruption of several cubic kilometers of basalt (McCartys lava flow, El Malpais). New Mexico has one of only three large mid-crustal active magma bodies (Socorro) in the continent. (The others are Long Valley, California and Yellowstone, Wyoming.) The Socorro area is one of the few areas where there is a dearth of young volcanoes, so perhaps the Rift is working on filling out its volcano landscaping.

                            Every major type of volcanic landform (composite volcano, shield volcano, volcanic caldera, major ash-flows, pahoehoe and aa lava, maar crater, fissure eruptions, cinder cones) occurs in New Mexico.

                            "There's gold in them thar hills!"


                            Our staff have prepared a free packet of information about gold panning in New Mexico (in PDF format 5.14 Mb). It includes a brief history of gold mining in NM, where to look, what equipment is required, what regulations apply and who to contact, and an extensive reference list.

                            Others have simply gotten old. I prefer to think I've been tempered by time.

                            by Just Bob on Fri Feb 15, 2013 at 06:59:26 PM PST

                            [ Parent ]

            •  Better explanation of "permanent crust." (0+ / 0-)

              I meant that no crust from before that point survives today - it's all been recycled.  And most of the continental crust today is much younger than the oldest parts.

              Pour yourself into the future.

              by Troubadour on Fri Feb 15, 2013 at 12:27:39 PM PST

              [ Parent ]

        •  kinda (1+ / 0-)
          Recommended by:

          99.9999% of the initial metal the earth formed with sank to the core and stayed there, but that was an Event and not a continuous process.

          The earth started out homogenous, because impacts don't generate enough heat to get that much magma to behave like water. It might flow, but it still has structure and behaves like a solid in many situations. Over time radioactive decay heated things up and softened the magma, allowing metal to separate out into big lumps, which had enough mass to start to sink, generating more heat and allowing smaller lumps to sink, etc. until everything was separated out like salad dressing. This happened very fast, and we cooled back down very quickly afterward. Once we did, there was no process capable of creating that kind of precipitation again. So gold from impacts 3.8 billion years ago is still dissolved in rock circulating in the mantle and erupting out of volcanoes.

          Also, veins are a geological thing and don't have anything to do with impact craters, and gold IS pretty evenly distributed. Meteor Crater has an abandoned mine in the center built on the (correct) logic of metal being delivered by asteroid impacts. The problem was the meteorite vaporized and the iron was all over Arizona instead of in the hole.

          •  I didn't say veins were associated with craters. (0+ / 0-)

            Craters on Earth are all young because of all the erosive processes.  Veins are the contiguous bodies of impacts as they've been stretched out and warped over long periods of time by tectonic movement.

            Pour yourself into the future.

            by Troubadour on Fri Feb 15, 2013 at 12:25:38 PM PST

            [ Parent ]

        •  Then why are volcanic mnts so rich in metal (0+ / 0-)

          compared to uplift mountains?

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