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Space Science

Tennessee Crater Inches Toward Recognition 113

Posted by Soulskill
from the denting-our-planet dept.
tetrahedrassface writes "Slashdot carried the story of an-as-yet unverified impact crater in Tennessee a couple of years ago. After a few weeks of fairly hardcore sample taking, digging, obtaining some good images and manipulating them, I'm proud to report the first batch of evidence in favor of it being an impact site. The primary smoking gun is the presentation of an astrobleme, obtained from High Resolution Ornithographic Images taken in 2008. Also of note are the melted/deformed rocks, magnetic crater dust, and the fitment of the crater rim to a circle. A rented plane and a bunch of photographs today and it's pretty obvious that it's a crater, folks. Cheers!"
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Tennessee Crater Inches Toward Recognition

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  • typo? (Score:5, Informative)

    by memnock (466995) on Tuesday August 28, 2012 @06:31PM (#41158893)

    ornithographic or orthographic?

  • Bird pics? (Score:5, Informative)

    by tqk (413719) <s.keeling@mail.com> on Tuesday August 28, 2012 @06:33PM (#41158923)

    ... High Resolution Ornithographic Images ...

    As taken by birds? Perhaps you meant orthographic? [wiktionary.org]

  • He's gotta be around there somewhere...
  • They fact they found a pair of boots next to a jug by the crater leads me to believe some ones still blow up on them.
  • by Shavano (2541114) on Tuesday August 28, 2012 @07:01PM (#41159277)
    Clearly the scientists behind this investigation are a trifle flighty.
  • Linking to a server via IP address on Slashdot, huh? Yeah, that's going to hold up.

  • by Anonymous Coward

    The primary smoking gun is the presentation of an astrobleme, obtained from High Resolution Ornithographic Images taken in 2008. Also of note are the melted/deformed rocks, magnetic crater dust, and unusual parts from the alien spacecraft that crashed there .

    Fixed that for you.

  • by Penurious Penguin (2687307) on Tuesday August 28, 2012 @07:31PM (#41159663) Homepage Journal
    Considering the relative proximity to this extremely badass crater [wikipedia.org], I'll consider it.

    On a different note; oh how beneath the glorious reign of Reinheitsgebot I'd love to have a corpulent barrel of dunkel in this place [planetoddity.com].
  • The last link (Score:2, Interesting)

    Looking at the last link - a photo - it's most certainly not "pretty obvious" it's a crater. given the area we're talking about, it could quite easily be the remnants of an old, rather large, sinkhole.

  • by crunchygranola (1954152) on Tuesday August 28, 2012 @07:49PM (#41159869)

    "A rented plane and a bunch of photographs today and it's pretty obvious that it's a crater, folks."

    Only if "crater" means "circular depression". Sinkholes make nice circular depressions also, and are far from rare in the South. And the summary misuses the term "astrobleme" which means "cosmic impact crater" and would be the whole circular structure. I gather the poster is referring to an elevated region in the center which may be an impact rebound peak.

    Melted rock and magnetic dust makes the case stronger (but ancient volcanism could account for at least the melted rock), but the real smoking gun that would make the case without any doubt would be coesite or stishovite (for example), quartz that has been transformed by megabar (millions of atmospheres) of pressure. These materials (or other evidence of extremely intense shock waves such as characteristic microfractures) are virtual proof of a cosmic impact.

    • You can't argue with the rebound ring in da bottom. :0

      • by Jodka (520060)

        You can't argue with the rebound ring in da bottom. :0

        That is literally true.

      • by capnkr (1153623)
        Here's a .kmz of the crater, take a look around: http://minus.com/lbuIRyUOrBNfXR [minus.com]

        Not much else in the area with similar depressed topology. Seems if it is/was a sinkhole, there would be more like it there or nearby to be seen.

        Dusty, I think it is neat that you are gathering this sort of evidence. Kudos! :)
        • Thanks, and the evidence gathering continues. I understand the bar is high. This was an update on a topic allowed to languish too long. :)

    • by Grishnakh (216268)

      Yep, I went to high school in east Tennessee. We had a big sinkhole open up right in the football field! Hahaha. Too bad they filled it in.

  • by Anonymous Coward on Tuesday August 28, 2012 @08:14PM (#41160149)

    Possible. But I'd sure want to exclude karst features (e.g., sinkholes) before accepting an impact origin for a topographic feature in a known karst area. Mapped karst features are awfully close to where the "crater" site is.

    Also, your shattercones don't look like real shattercones [wikipedia.org], which have a nested, cone-shaped geometry. What you illustrate looks more like an ordinary concoidal fracture [wikipedia.org]. Break a rock by any method and you can get those.

    If you want to identify impact melt convincingly, then ordinary macroscopic pictures won't do. You need a thin section [wikipedia.org] and some petrographic microscope work. Sometimes even forest fires can melt rocks on the surface, or a camp fire if it is big enough.

    Some terrestrial minerals are highly magnetic, but also quite resistant to weathering, and will get left behind (and even concentrated) while other minerals are altered. For example, magnetite [wikipedia.org]. If it were demonstrated to be metal (i.e. unoxidized), especially if a combination of iron and nickel, that would be suggestive, but you'd still have to exclude man-made contamination.

    Missing from your sampling is context. Disconnected rocks removed from their geological context are not as useful as understanding how they were arranged in the field. This is especially true for features like shattercones, which should have a clear geometrical relationship to the crater (i.e. basically a radial arrangement). If you are sampling from rubble on the surface, rather than bedrock, you really don't know what you've got. It could be transported by river, gravity (mass wasting), or (not sure if possible at this location) glaciers. It might not even be local. A lot of your samples have lichens and weathering rinds suggesting that these aren't particularly fresh samples (this is why geologists bring geological hammers and suitable eye protection to use them).

    In short, you've got an interesting feature, but you are still far from demonstrating it is a crater.

    • Yeah a lot of sinkholes have astroblemes...

      • by Anonymous Coward on Tuesday August 28, 2012 @10:15PM (#41161257)
        I am a geologist, a quick look at the 24k topographic map for the quadrangle this circular depression is found in shows that there are dozens of karst features in the area (sinkholes). There is even a disappearing stream (classic feature of karst terrain) that occurs ~1.8 km southeast of the questioned feature. I could give location information for some of these karst features if Tennessee was mapped using the Public Land Survey System, but it is not (no section numbers). Given the fact that the area in question is mapped as heavily weathered Ordovician/Cambrian dolomite, and that there are dozens of other karst features, it is very likely that this is a huge sinkhole. I agree with what AC that posted above, your shattercones do not look like real shatter cones, they look like concoidal fractures. Also an impact event will leave a set of radial fractures in the bedrock that could be easily mapped on a rose diagram. In order to conclusively prove impact melt, thin sections will absolutely be required as AC above states. The only way to look at shocked quartz grains, if present, is via thin sections and a polarizing light microscope. You also mentioned that topsoil was pushed into the middle of this feature after logging was completed, because the material at the bottom of the pit is from outside, you would need to dig a trench through the foreign material to get to material that is actually from inside the depression. Surface samples are not enough, the rocks you found could have been weathered rock pushed in with the soil. I suspect that if trenching is done, breakdown blocks from the roof of the collapsed cave below would be found. The gravel you note in your evidence of ejecta, would have to angular and composed of heavily altered rock found within the pit, if the gravel is rounded at all it was transported by water, not a blast.
        • by tetrahedrassface (675645) on Wednesday August 29, 2012 @04:32AM (#41163597) Journal

          I fully intend on getting thin sections done. The gravel IS angular. There are heavily deformed Ordovician Age rocks. Unfortunately, where this area is a Karst area. You can't pick up the feature and move it to an area that makes it easier. Is this a Karst feature? I doubt it very seriously. However thin sections for shocked quartz are next on the list. I appreciate the time you took to reply. No topsoil was never pushed into the middle of this feature. Yes, a road was cut in pushing regolith into one corner and making it look a lot squarer than it is. I know the full history behind the site going back over 120 years. There is rounded material i.e. (sand) in the soil around the crater at a microscopic level because the soil is 200+ million years old and already contained HEAVILY WEATHERED ancient rock..

          The investigation continues. Thin samples of severely deformed rocks are next.

          • Re: (Score:2, Insightful)

            by Anonymous Coward

            I wouldn't worry too much about the squarish shape. It's close enough that I don't think the shape in map view is an obstacle to it being an impact crater, especially if it has experienced weathering. You mention Barringer Crater [wikipedia.org] which isn't perfectly round either, and that's a fair analogy. However, all the other issues mentioned still stand. There are an awful lot of ways to make a roughly-circular pit in the bedrock geology, especially in a karst area. Generally speaking, if we were on Mars or the M

            • by CptNerd (455084)

              I grew up in Middlesboro, Kentucky, and it took quite a few years before it was determined that the valley was actually the remnants of a meteor crater. I remember going past the huge USGS map that hung along one wall of the mall and seeing the obvious circular shape of the valley, especially when the kinds of rocks were identified with different colors, it formed a definite bulls-eye. Most noticable was the description of "shocked quartz" in the valley rocks, and the small raised area in the center of the

      • You keep using that word... it does not mean what you think it does.

  • by wbr1 (2538558) on Tuesday August 28, 2012 @08:28PM (#41160259)
    Of course it is inching. It is, after all, riding on a tectonic plate!
    • by TimKemp (677202)

      Which is riding on the back of a gigantic turtle.

      • by wbr1 (2538558)
        IF YOU KNOW ABOUT THE TURTLE, DO YOU KNOW WHO I AM?

        Stupid slashdot filter. I wanted to make a funny response, for those of us who know an love Pratchett, but no, I have to type a bunch of stuff not caps to evade the filter. Grrrrrrrr.

  • Age of Crater (Score:2, Interesting)

    by paleo2002 (1079697)
    The crater is in Hamilton County which is along the southern border of the eastern part of the state. Looking at a geologic map of the region, the county is sitting on rocks from somewhere between Cambrian and Ordovician in age (about 540-440Ma). However, the region's geography is dominated by a thrust-and-fold mountain belt that formed during the Alleghenian orogeny about 325-260Ma. The crater is undeformed so it has to post-date the collisional event. Its definitely less than 260Ma. Considering how s
  • by mbone (558574) on Tuesday August 28, 2012 @08:30PM (#41160281)

    The smoking gun will be shocked quartz.

  • by Anonymous Coward on Tuesday August 28, 2012 @09:03PM (#41160591)

    Sorry, I'm not seeing it. Everything I see posted here can be adequately explained without the presence of an impact. Sinkholes are also often round. Magnetic material can accumulate in and weather out of most rock types, and can be introduced through secondary contamination. Vugs are, and other holes/porosity often are, the result of dissolution and weathering (coincidentally, the same processes form sinkholes under the right conditions).

    To convince me, do several things:
    1. Cut open the weird looking metal pieces and acid-etch them to reveal any Widmanstätten patterns. (Note: the metal in meteors will not react quickly to water or other weak acids, but limestone will. Iron minerals commonly occur in most rock types, not least of all sedimentary rocks, including limestone, that are likely to form sinkholes. Magnetic minerals are actually pretty common. I'd be a little surprised not to find small grains of magnetic material pretty much anywhere on Earth.)
    2. Take the rocks to an expert and get an opinion. This often annoys most geologists a little bit since, as one recounted to me, he's had hundreds of people bring him "meteorites" over the years and precisely zero of them were actual meteorites. But if you can get an appropriately trained geologist to glance at them it should be moderately easy to see that they are or are not meteorites, or represent a rock that has melted. If that person can't say definitively, he/she may be sufficiently intrigued to investigate further.
    3. If the rocks look interesting to the geologist, running through an electron microprobe and electron microscope will reveal many more interesting things about their precise chemical composition and microscopic structure, as will thin sections under an optical microscope. For the metallic parts reflected light microscopy will tell a great deal. The presence of certain high pressure SiO2 polymorphs is diagnostic in rocks from the impact zone, and iron/nickel composition is a very good indicator in a suspected meteorite.
    4. Careful mapping will help, as will a geologic map of the area. Geologic mapping is not difficult, but defensible results require practice and a thorough understanding of geologic principles. Look for the character of the ground, the distribution and size of different material both vertically and laterally, its composition, texture, the nature of contacts between areas with different materials, and the orientation of any different layers, amongst any other notable characteristics. Relate your findings to those on existing geologic maps. Create your map on top of a high resolution topo map.
    5. Consider multiple working hypotheses, and keep an open mind. For example, the two obvious hypotheses are that this feature represents a sinkhole or that it instead represents an impact crater. Find as much evidence as you can that contradicts or informs both of those ideas; consider all evidence in light of them. For example, you might observe that the area is characterized by shallow crystalline silicate metamorphic bedrock that is not subject to dissolution, thus pointing away from a sinkhole origin. On the other hand, you might note there are caves in the area, topographic maps show creeks and stream ending abruptly, that there was cement production there in the late 1800s, limestone clasts show traces of pyrite, and there's little evidence of breccia.

    It's a logical fallacy to conclude an unusual process must be responsible for an observed feature when your evidence can be adequately explained by more pedestrian processes. Make sure you have solid evidence that can't be explained by more mundane processes before jumping to a novel conclusion -- ad hoc conclusions are inimical to real understanding and the process of science. If an impact is still a reasonable explanation after carefully considering your evidence in light of other hypotheses, systematically write up your findings. Start by giving an overview of the general area, then the feature itself, then the details of specific observations you've made a

    • by T Murphy (1054674)

      It's a logical fallacy to conclude an unusual process must be responsible for an observed feature when your evidence can be adequately explained by more pedestrian processes.

      Exactly why I think the simple solution to this is that he found a sinkhole that was impacted by a meteor.

  • by PPH (736903)

    That's where Uncle Jeb's moonshine still blew up in 1925!

  • Can someone please check my impact crater candidates? Maybe they have already been determined.

    • Re: (Score:2, Informative)

      by Anonymous Coward

      Number 1 is Hicks Dome, a structural dome related to igneous processes.

      Number 2 looks like erosion at the interface between different geologic layers, probable a ridge of Monongahela Group sandstone and softer Conemaugh Group shale and siltstone. There's nothing about it besides a little bit of roundness that's very crater-like. If this structure has a name I don't know what it is. The fact that it appears to be at the intersection of topography that's very steeply eroded to the west and more subtly incised

  • where is Tennessee, azeroth or tyria?
  • I don't think that it is "pretty obvious it is a crater". Prime evidence is missing or not well enough illustrated.

    First:

    1) as others here remark too, a circular feature does not equal an impact crater. Karst depressions are circular too and a strong candidate in this area;
    2) magnetic particles can be found in any soil. They do not point to impact as such. Show us geochemical tests that show they are of meteoritic composition, and show us that they have an abundance well over the natural accretion rate
  • I've tested these with acid. If the sample won't react with boiling acid (nitric or sulfuric) why would it stand to reason they are carbonates reacting to rainwater?

  • http://goo.gl/maps/jgJyJ [goo.gl]

    Note that the photo with the houses at the very top would be taken from the eastern edge of the map with those houses being along Pierce Road pretty much straight over from the bottom "-" of Google Maps' magnifier tool. From the ariel view it could be a sinkhole or a crater, with sinkhole being more common in the area. Someone mentioned below that there is a disappearing stream just a mile from there. That part of Tennessee has some magnificent caves.

    Anyway, I hope the poster will

    • Thanks, and that's it exactly. Honestly, the rocks are way too deformed for it not to either be an impact crater, or... pehaps.. a Kimberlite tube of large proportions... but, it could be a monster cave, in which case that's cool too. I'm in this for the science, not trying to internet famous or a impact crater finder.You can bet I'm going to keep on it. It's fun.... and it's interesting.

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