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Prehistoric meteor shower?
tty
post Dec 13 2007, 07:02 PM
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A real weird news story from Nature about meteor damage to pleistocene fossils:

http://www.nature.com/news/2007/071212/ful...s.2007.372.html

If traces of this meteor shower has been found in both Siberia and Alaska as the story implies, then multiple impactors must have been involved. Such small meterites would lose speed quickly so the airburst must have occurred at fairly low altitude.
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Rob Pinnegar
post Dec 14 2007, 04:00 AM
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Yeah, I read this one the other day. Very peculiar (and, really, more-or-less unbelievable).

It should at least be interesting to see how it develops.
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helvick
post Dec 14 2007, 08:55 AM
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QUOTE
The discovery of the 2–5 millimetre holes left by meteorites opens a window into a impact event thought to have happened over Alaska and Russia tens of thousands of years ago.


I can't see how this could be possible.

They are proposing that millimetre/sub-millimetre meteoric debris could have reached the surface at a sufficient velocity to penetrate bone to a depth of a few millimetres and done so over a geographic area thousands of kilometers across. I don't see that being at all likely - such small particles have a very limited range at such velocities (a few km at most) and if the velocity rises too far they will vaporize and any low altitude airburst that is small enough to generate the debris shower without a cataclysmic shock wave that would have totally destroy the tusks could not be large enough to cause similar effects across such a large range.

I would also describe this sort of provenance for evidence as a bit suspect:
QUOTE
West bought the 60-centimetre tusk for about US$200, and later headed to the warehouse of the company that he bought it from: Canada Fossils.

If you ask me it is easier to think that the damage he has detected was caused by someone doing some welding near those tusks at some point in the past rather than micro meteorities peppering mammoths and bison during a prehistoric mega meteor storm.
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As old as Voyage...
post Dec 16 2007, 12:47 PM
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The idea that these animals were present and in the immediate vicinity when a meteorite hit the Earth is interesting. However, I find it quite unlikely.

To me, a much more plausible explanation is that our ancestors were hunting with meteorite material. All they had to do was find an iron meteorite, smash it into sharp shards and attach the shards to wooden poles to form an effective hunting spear.

The meteorite material embedded in the tusks and bones would therefore simply mark the impact point of such a weopan.


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helvick
post Dec 16 2007, 02:51 PM
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Now that's a much more plausible explanation - good thinking there.
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TheChemist
post Dec 16 2007, 03:03 PM
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QUOTE (As old as Voyager @ Dec 16 2007, 02:47 PM) *
The meteorite material embedded in the tusks and bones would therefore simply mark the impact point of such a weopan.


From the article : "Some of the tusks are peppered with hundreds of the fragments, which had burnt grooves into the bone. All the pieces entered the bones on the skyward surfaces of the tusks and skull."

The quantity of the fragments, along with the fact that they burned the tusks on their way in suggests spears or arrows are not likely explanations.
Unless prehistoric people made bullets out of meteorite fragments smile.gif

Edit : A lot more information in the poster from AGU.
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djellison
post Dec 16 2007, 03:03 PM
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There are records of ancient people using meteoritic material in tools etc - they were highly prized as they didn't know how to make their own metal at the time. Makes a LOAD more sense to me. Little fragments wouldn't be travelling at high speed. They'd loose all their energy really quickly. (consider the old penny-from-tall-building myth - which is indeed a myth)

The chance of a fragment small enough to make those marks, travelling fast enough to make those marks, and 'hot' enough to scortch them...sorry - I find that very hard to believe
Doug
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nprev
post Dec 16 2007, 06:34 PM
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Weird story. The only other alternate explanation might be a Tunguska-style event in which the impactor basically detonated near the ground & spread shrapnel far & wide. However, this is difficult to envision for a typical iron/nickel meteorite; perhaps a cometary body with complex composition (as we've seen hints of in Wild-2 from Stardust?) huh.gif


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Rob Pinnegar
post Dec 17 2007, 01:05 AM
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Well, here's a thought. Let's assume for the moment that things happened the way the authors suspect they did.

One of the key points here is the geographic distribution of the bones. Keep in mind that we're talking about very small fragments of meteorite here. Thus the animals in question might not have been killed by the impact. They may have subsequently wandered a long distance before eventually dying -- throughout Alaska and over the Beringia bridge into Siberia.

Thus the impact event could have been localized to Alaska.
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nprev
post Dec 17 2007, 02:42 AM
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I've always wondered about this particular (apparent) astrobleme in Alaska. If it is in fact a hit, it looks pretty fresh; still has a semicircular aspect, and Alaska is nothing if not geologically active...ask me how many quakes I felt when I lived there, 2001-2004... rolleyes.gif
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dvandorn
post Dec 17 2007, 06:35 AM
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You know, any really energetic impact will create secondary projectiles. I can imagine that there would be a "ring" around an impact site where the ejecta would still be red-hot when it landed. That ring could be pretty large, depending on the size of the impact, the characteristics of the target, etc.

Besides, I would think that something coming in at cosmic velocities would shatter a horn or a bone, not burn a hole into it. I don't think the described damage necessarily requires that the objects which hit these beasts to have had the speed of a primary impactor.

-the other Doug


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tty
post Dec 17 2007, 06:26 PM
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More details here:

http://news.bbc.co.uk/2/hi/science/nature/7130014.stm

It looks as if there might really be something in it. If it happened 30,000 years ago, then humans are out - there weren't any in Alaska at that time, and if there are signs of bone growth afterwards then it obviously happened while the animals were still alive.
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nprev
post Dec 17 2007, 09:35 PM
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Huh. That's pretty damn scary, really. What could cause a metallic body to apparently, literally explode to the degree needed to generate small high-speed fragments like this? All I can think of is a VERY high impact velocity that basically melts the thing in a few milliseconds, but that sounds screwy to me, too... huh.gif

My previous Tunguska-style scenario doesn't sound plausible, either. I don't see why any chunks of iron-nickel wouldn't survive the explosion of the volatiles more or less intact instead of shattered into shrapnel.

There's a big piece of this puzzle missing. A lot's going to depend on the actual age of the fossils. If it's later then the colonization of North America, then I'd definitely favor the spearhead theory (IIRC, 30Kyears is still just barely within the realm of possibility for human migration to the Americas).


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tty
post Dec 17 2007, 11:42 PM
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Here is a link to the actual AGU poster:

http://ie.lbl.gov/mammoth/AGUSF_poster_2.gif
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tasp
post Dec 18 2007, 07:11 AM
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{sorry, did not pay to read entire article, if this has been ruled out . . . whatever}

Any chance we are seeing the effects of a lightning strike in proximity to the mammoth, and perhaps a rocky outcropping of an appropriate ore ??

Even an unlikely lightning effect seems, on first glance, similarly probable to an (unprecedented?) meteoritic phenomena.
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