[meteorite-list] Mammoth Stew

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Mon, 17 Dec 2007 17:52:07 -0800
Message-ID: <93aaac890712171752m2ae6368yac4b67916e396216_at_mail.gmail.com>

Sterling, All,

> 1. The point of comparison to Tunguska is that
> an airburst is radically different from a ground burst
> and leaves, proportionately to its intensity, remarkably
> few discernable markers.

Right, but seeing as the effects from the event of which we speak
differ greatly from those of your comparison, it seems an unworthy one
to make. Yes, an unknown phenomena might create such a set of effects
as are geologically evident, but just saying "it's possible" is
something that I acknowledge as well; we all know that Tunguska events
occur and that, evidently, astronomical events that create the
geological evidence that we've found occur. But that still in no way
ties the two together.

> 2. The statement that the Earth and Moon haven't
> "always" shared the same orbit is quibble for quibble's
> sake. The collision between the two occurred in the
> first 100 million years or possibly much less of the
> solar system. The Australian zircons say more than
> 4.46 billion years. The mutual collision disassembled
> the Moon and melted the Earth into the mantle, so
> the surface record starts or is re-set at that point. (I
> think that the proto-Moon formed at one of the Earth's
> Trojan points. A Trojan is only stable if the mass of
> the Trojan is insignificant compared to the primary
> orbital mass; once it grows to a measurable fraction,
> it is perturbed "along" the orbit until it is "captured"
> by the primary. That's how the Earth and Moon got
> hitched, sez the witch doctor, poking the fire...)

Right, but we might as well play along with the rules...I wasn't
trying to focus on that, and said as much, but by all means, explain
away - I was simply stating the obvious.

> 3. I am only counting impactors that result in a 1000
> meter crater or larger.

...Well now that we know...

>Atmosphere not a factor in that
> size range. The fact that the Earth has "new" craters of
> only 10 meters diameter demonstrates our atmosphere
> only "protects" from mere nuisances and nothing more.
> Moreover, you imply that it is "easier" to make craters
> in the Moon (your incorrect fist-sized impactor, six meter
> crater), and that is not true.

KE = 1/2mv^2. With no atmosphere, a fist-sized, say ~1kg stone,
moving at, say, 35km/s, makes 35,000 Joules of energy in coming to a
stop. I read the "fist-sized = 6m" bit from a book somewhere, and it
stuck in my mind; I don't know if it's entirely accurate, but given
the high velocities involved and the apparently rather large amount of
energy released by such an impact, I see no reason to disbelieve this,
especially as large parts of the moon are covered in at least a few
feet of easily-cratered soft dust. Even if such a release of energy
wouldn't make a 6m crater in some of the more rocky regions of the
moon, I'm fairly sure that 35,000 Joules would make a decent-sized
hole easily enough.

>The ratio of impactor energy
> to crater size is the same for both bodies, both of which
> have the same crustal density. The Moon is surfaced
> entirely with "tougher" rocks (basalts largely) and not
> overlayed with "soft target" to the extent of the Earth
> (all that water? half a kilometer of clay?). Further, the
> Earth's gravity accelerates an approaching close object
> by an additional 11,200 m/sec in velocity over its distant
> relative velocity, while the Moon only adds a measly
> 2380 m/sec. It's HARDER to crater the Moon than
> the Earth, on a crater by crater basis.

Eh, how about a meteorite coming at the earth, with the moon in the
way? But this isn't the point - you mistook mine. My point is that
given a fist-sized body striking the moon and the same body entering
the earth's atmosphere, there will be drastically different impacts.
I don't know where you draw the 1km crater line, as, in my opinion,
such a body might well break up if it entered the atmosphere at a
shallow angle, but who's to say....

> 4. You used the puzzling phrase "such a small impact"
> in response to my having modeled an impact that was
> 8% of a Chicxulub and still wouldn't have punched
> through the Pleistocene ice cap! What does it take for
> you to call an impact large?

I didn't use that phrase when referring to your calculations regarding
the 10km comet, but to that end, it still seems highly unlikely. A
thirty-degree impact is highly unlikely, and I'm thinking that an iron
impactor would do a bit more damage than a comet.
Do you, by any chance, know what the composition of the dust layer (if
it would suggest such a thing) points towards the composition of the
body having been?
I just don't see much metallic residue coming from a comet, though I
suppose there would be some.

> As for traces, we have lots
> according to the Firestone gang: nanodiamonds, carbon
> layer, bucky balls, metallic residues, blah, blah, all many
> thousands of miles away from the impact point. Actually,
> I have to thank you for (unintentionally) starting me down
> the path toward modeling "impacts in ice caps." Such
> thick emplacements cover 10% to 20% of the Earth's
> surface during glaciations, yet leave few traces of even
> a major impact: no rock melt, no impactites, no crater,
> no tidal waves. We've ignored this possibility completely
> up till now. Note that the traces the Firestone gang have
> found seem to be able to be formed entirely from the
> impactor? That is what would happen in an "ice cap hit"!
> There would be those bothersome shock waves, the
> injection of a huge amount of water vapor into the Earth's
> atmosphere, after the wildfires from the thermal flash, of
> course. I don't think this obvious possibility has ever
> been "thought through."

Well it has now...and I won't say that it's not possible, but we seem
to be in agreement anyways - my point was that if there were a large
crater, we would undoubtedly have found it, and you're telling me that
there is no crater. We're arguing different angles of the same
side...

> 5. You say, "most of the craters were formed before
> the [recent?] timeframe." Well, that's exactly what the
> argument's about, isn't it? This is the comfortable, "that's
> all in the past" argument.

It's not all in the past, nor have I ever said such a thing. That
said, there were more impacts two billion years ago than there are
today, and you know that as well as I do.

>Let's review the cratering history
> of the solar system. After initial accretion, a tapering off.
> Then, at 3.8 to 3.9 billion years ago, an intense episode,
> the "Late Bombardment," followed by an exponential
> decline for more than 3 billion years. Then, at 0.6 billion
> years ago, cratering rates begin to rise dramatically, until
> 0.4 billion years ago, when they have increased fourfold
> in 0.2 billion years. They again decline. until 125-100 million
> years ago, when they increase, roughly doubling. If nothing
> else, this demonstrates that the system impactor flux varies
> dramatically through solar system history, for whatever
> reason. The role of comets, stellar encounters, Oort Cloud
> shenanigans, asteroidal family dustups is all unclear and
> yet to be pinned down. Good old ignorance. But the view
> that solar systems start in an impact squabble and then
> settle down happy forever is dead wrong. Perhaps, after 4 or
> 5 billion years, long-tern inherent dynamic instabilities catch
> up with a solar system and such systems begin to pummel
> themselves to death. We don't know. Find me a 10 or 20
> billion year old stable solar system... Maybe such contrivances
> as solar systems just don't last? We are always (see the press
> releases) finding very young solar systems; have you ever
> noticed our finding a very old one? Me, neither.

This all goes to support what I said. Most, of the phases of which
you speak occurred after the moon's surface had cooled, and since
then, in general, there has been a decline in the amount of rubbish
floating around.
So more craters were being made, say, two billion years ago, than were
being made ~30,000 years ago.

> 6. You call the 3,000,000 crater figure a "prejudiced number."
> You are simply wrong about that.

No, I'm right. Your number may be right, but we should be dealing
with a different number when discussing impacts of which traces could
still exist on earth today, vs those we can see on the moon. We're
dealing with time here, as well as the number of impacts, and just
taking the number of impacts over the past two billion years that the
moon has had a solid surface simply doesn't work when we can't see any
trace of a 1km crater that formed on the earth as many years ago. I'm
not trying to say anything about the number of impacts that have
occurred on earth over that time frame, because I assume that it would
correlate with the age of the moons surface. What I'm trying to say is
that given that there are x number of craters on the moon, we would
need to know the age of each to determine a good number for the rate
of impacts over the past, say, 50,000 years, which would be relevant
to this discussion. We aren't talking about 2 billion years ago,
we're talking about 30,000 years ago. Times - and rates, change. We
should be working with the current ones.

>That's the number of craters
> made on Earth; I didn't say they survived. Oh, it could be off
> by 300,000 craters either way, but it's "order of magnitude"
> correct. What the current rate is -- that IS the dispute, to be
> determined, not dismissed. Cratering, where we are able to
> closely date it, appears to demonstrate "clustering." If impacts
> come in intense episodes of 50,000 to 100,000 years with
> deep calm between... Well, that means a "local" rate can be
> radically different from a long-term time-averaged rate. What's
> the impact weather like this era? That's the question. It depends,
> in scientific terms, on whether cratering is entirely "stochastic"
> or not. If there are "mechanisms" of cratering, it's not. Since
> we know of several obvious mechanisms (the breakup of
> major asteroids, comet infall from outside perturbations), it
> does not seem likely that the process is stochastic or perfectly
> random. If it is not, the comfortable notion that "such things
> don't happen anymore" is unsupportable.

Did I say that? I don't think I stated, anywhere, that large impacts
"don't happen anymore." They don't happen generally at the rates at
which they used to (there used to be more of them)...that was my
point.

> 7. The insistence on perfect matching of extinction and impact
> timing is a red herring. In massive impacts (K-T, the Permian
> Wollop), yes, it should be close. But extinction can be "smeared"
> out over thousands of years by environmental change. The fact
> IS that 10,000 years ago, there were flourishing some 300-odd
> major (big) mammal species that I've never seen and never will.
> They had all been through de-glaciations before, so it wasn't
> that. Either "something" happened or Man the Mass Murderer is
> responsible. (A ridiculous theory; when game is scarce, you move
> on and game recovers. Neolithic man never hunted game down to
> extinction. It takes so long, you'd starve first. They weren't stupid,
> you know. They were opportunists, and they lived off the fat of
> the land, not the lean.)

Well, then climate change could well have been the culprit - but what
cause the climate change is, I think, still open to discussion.
All I've been saying is that I don't think we're going to find a
crater because there isn't one to find, given that it would be of a
young age, large (if it existed), and we would thus have already found
it. - And that those iron bits, if they are from a meteorite, didn't
come from the culprit that caused the climate change, because the
dynamics of an impact that could both produce such bits of iron and
cause global climate change, without badly searing the bones, do not,
in my opinion, exist.

Regards,
Jason

>
>
> Sterling K. Webb
> --------------------------------------------------------------------------
> ----- Original Message -----
> From: "Jason Utas" <meteoritekid at gmail.com>
> To: "Meteorite-list" <meteorite-list at meteoritecentral.com>
> Sent: Monday, December 17, 2007 12:58 AM
>
> Subject: Re: [meteorite-list] Mammoth Stew
>
>
> Sterling, E.P., All,
>
> > For the record, I like my peppered mammoth
> > with lemon butter...
>
> Thick-cut, salt and pepper.
>
> > Jason, think about Tunguska. A 25 megaton airburst
> > that left no crater, no pits, not even the tiniest, no
> > material remains whatsoever, no isotopic traces in
> > reliable amounts, nothing with a side order of zilch.
> > (Ok, possible microscopic spherules in trees, not
> > 2-3 mm particles, and disputed to boot).
>
> Exactly; nothing was left; no evidence, no anything.
> How, so, can you relate this to Tunguska, when the evidence that we
> have for it is completely different?
>
> > Yet, had it occurred over Belgium, it would have
> > killed 90% of the population of the nation, or if over
> > metropolitan London simply removed the world's
> > then-largest city from the map. IF we did not have
> > the Russian newspapers, the native reports, Kulik's
> > photos of the trees (gone now), could anyone today
> > detect that it had ever occurred? And it hasn't even
> > been a lousy century! (The Centennial is next June!)
>
> But you're lacking the isotopic evidence, etc. Not so with this layer
> of...whatever it is.
>
> > Like a belief in the existence of the atom or any other
> > thing that we cannot and never will see with our own
> > eyes, vast numbers of craters have covered on Earth.
>
> Mhm...
>
> > 1) The flux of impactors at the Earth is identical to the
> > flux of impactors at the Moon, since the two bodies
> > occupy the same orbit and always have, the Moon like
> > a celestial tick on our neck.
>
> Well they haven't always, but, irrelevant to this discussion.
>
> > 2) The pristine state of the Moon allows for a very
> > accurate count of the number of impactors that have
> > struck the Moon (allowing for extrapolation for the
> > areas covered by flood basalts -- ~170,000 impactors
> > producing craters of one kilometer or more).
>
> Fine, fine, information we all know.
>
> > 3) It's mathematical child's play to scale up the lunar
> > impactor flux to the Earth's size and add in the increase
> > in "gravitational" cross section caused by the Earth's
> > stronger gravity (13.5 + 4.4 = ~18 times more impactors).
> > Not only that, but the stronger terrestrial gravity means
> > that ANY impactor will make a bigger crater on the Earth
> > than it would have if it had smacked the Moon instead.
> > (And for impactors that would make a crater 1 km or
> > more in diameter, the atmosphere is not a factor.)
>
> Well, we also have to take into account that a fist-sized meteorite
> will make a crater six or so meters across on the moon whereas on
> earth such a thing would make nothing more than a pretty light show.
>
> > 4) So we can easily determine the number of craters on
> > the Earth. No problem. The Earth has had approximately
> > three million (3,000,000) impactors, so we must have
> > three million (3,000,000) craters over one kilometer in
> > diameter!
>
> Subtract the smaller craters and account for erosion...we're talking
> about the past fifty thousand years, not 2+ billion. The number of
> impactors over this timeframe was smaller than that of before, and
> erosion has taken a lesser tole on such craters, as they're younger.
>
> > Before we all run outdoors to check out the vista of
> > craters, craters, craters everywhere -- sorry, they're gone.
> > After counting craters from the obvious to those hidden
> > to the eyes of all but gravitometers, 17,999 craters out of
> > every 18,000 craters have vanished utterly from the planet
> > without a trace!
>
> See above...this makes sense given that most of the craters were
> formed before the timeframe that is of any importance to this
> discussion.
>
> > So, both these statements are true, in their fashion:
> > a) The Earth is the most cratered body in the solar system.
> > b) The Earth is the least cratered body in the solar system.*
> > (* except for the other really interesting place... Titan)
>
> Well, maybe, maybe not...Mars should probably be more so.
>
> > >From 98,000 years BP to 14,000 BP, a northern polar
> > ice cap was in place, yes, with retreats and advances,
> > recensions and excursions, in this area or that area, or
> > all areas, changes whose precise timing is hard to pin
> > down, but for ALL of that 84,000 years, there was a
> > land based ice cap in most of the northern hemisphere,
> > varying in thickness from 1000 meters to 3000 meters.
>
> Right-o.
>
> > Two miles of vertical ice. Now gone. What traces
> > of a crater in its upper surface do you expect would
> > survive? Just for fun, I went and modeled on the LPI
> > Impact Calculator a Ten Kilometer Comet a little less
> > dense than water making a 30-degree impact, releasing
> > 8 million MegaTons TNT [or 8 TeraTons] energy
> > equivalent, and its crater wouldn't have reached through
> > an ice cap that thick; the crater was only 1100 meters
> > deep. Also, I don't know if anyone has seriously
> > analyzed a cratering event in deep ice! Ice, hard as
> > it seems, has properties midway between weak rock
> > and deep water (which produces much shallower
> > craters than rock).
>
> But we have to account for a crater (well, impactor at least - or
> maybe just call it a 'body') large enough to deposit such a layer of
> dust, and I don't think that you're going to get that from such a
> small impact.
>
> > Call the Earth the Eraser Planet. The Ice has to be one
> > of the best of the many erasers available. Three million
> > craters and only 170 of them still show... It's almost like
> > "they" were trying to trick us into an unreasonable
> > complacency, isn't it?
>
> See above...your numbers are off due to a prejudice towards older
> craters that were undoubtedly more common - and have suffered a great
> deal more due to the effects of weathering.
>
> > We've had a lot of questions about the difference
> > between an asteroid impact and a comet impact.
> > The difference between an asteroid impact and
> > a comet impact of similar energy? The outcome
> > of each is different, though the crater's the same size:
> > http://www.news.uiuc.edu/scitips/02/1025craters.html
>
> Right, and what it comes down to is size.
>
> > Surprised to find this, as I've never heard it mentioned
> > before: a 10-yr-old study, the last by Gene Shoemaker,
> > that demonstrated a He3 extraterrestrial dust layer at
> > 36 million years ago that persisted for over two million
> > years and overlaps the times of the Popagai and the
> > Chesapeake Bay craters. He considered it the evidence of
> > a period of "comet showers." But other events are also
> > possible explanations.
> > http://mr.caltech.edu/media/lead/052198KF.html
>
> How big are those craters again? If I recall, at least the Chesapeake
> crater is fairly sizable...
>
> > One of the disadvantages of being a short-lived creature
> > with a recording civilization only a few thousand years old
> > in a universe 15 billion years old is the problem of detecting
> > threats that do NOT leave long persisting warnings behind.
> > Instead of 3,000,000 craters, there were a few, so we were
> > able to deduce the rest, but only in the last (less than) 50
> > years.
>
> Prejudiced number...
>
> > We should not assume that we have now identified all
> > possible threats from the universe at large. A threat event
> > with few trace markers could be quite frequent and still be
> > very difficult to detect in the absence of such an event.
>
> Well, mass extinctions should give us something of a clue even if we
> can't find traces of an impact, but if I'm not mistaken, the mass
> die-outs occurred several thousand years after the dust layer was laid
> down, no?
>
> Regards,
> Jason
>
> >
> > Sterling K. Webb
> > ----------------------------------------------------------------------
> >
> > ----- Original Message -----
> > From: "E.P. Grondine" <epgrondine at yahoo.com>
> > To: <meteorite-list at meteoritecentral.com>
> > Sent: Sunday, December 16, 2007 8:05 PM
> > Subject: Re: [meteorite-list] Mammoth Stew
> >
> >
> > Hi all -
> >
> > 1) From the descriptions, the spherules in the tusks
> > appear to be the result of the condensation of iron
> > plasma, the same as at Barringer crater.
> >
> > 2) When Nininger did his survey of spherules at
> > Barringer crater, I doubt if he looked several hundred
> > miles away from the crater - that's what I think of as
> > a ballistic re-entry. The internet site for this
> > impact has been greatly improved, and I'm sure that
> > some here must have been active in that.
> >
> > I don't know about winds at the time of Barringer
> > impact, but I can't remember any statement as to angle
> > of impact. But then I can't remember many things
> > anymore.
> >
> > 3) I have no idea what the spherules' temperatures
> > were when they landed - but my guess is that they must
> > have been too high to use any type of barrel to
> > duplicate their hitting the bones. My guess is that
> > magnetic suspension and acceleration would be about
> > it.
> >
> > 4) As far as locating the 31,000 BCE crater goes, its
> > possible that the situation might be similar to the
> > K-T crater - that one took 10 years to find. Same
> > goes for impact point(s) for the 10,900 BCE event. If
> > you look at impact crater distribution maps, you'll
> > see that more have been found in the areas where
> > geologists live.
> >
> > good hunting,
> > E.P. Grondine
> > Man and Impact in the Americas
> >
> >
> >
> >
> > ____________________________________________________________________________________
> > Be a better friend, newshound, and
> > know-it-all with Yahoo! Mobile. Try it now.
> > http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
> >
> > ______________________________________________
> > http://www.meteoritecentral.com
> > Meteorite-list mailing list
> > Meteorite-list at meteoritecentral.com
> > http://six.pairlist.net/mailman/listinfo/meteorite-list
> >
> > ______________________________________________
> > http://www.meteoritecentral.com
> > Meteorite-list mailing list
> > Meteorite-list at meteoritecentral.com
> > http://six.pairlist.net/mailman/listinfo/meteorite-list
> >
> ______________________________________________
> http://www.meteoritecentral.com
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
>
Received on Mon 17 Dec 2007 08:52:07 PM PST