[meteorite-list] Comet: Talking Points, #1

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Mon Jul 24 09:26:50 2006
Message-ID: <20060724132635.94390.qmail_at_web36915.mail.mud.yahoo.com>

Hi all -

A superb analysis, but...

In the case of Rio Cuarto impacts, I have been
informed by a tree ring specialist that tree rings
show the climatic collapse dead on at 2360 BCE. (It
would thus appear that the correlation problem for the
Mayan calendar has been solved.)

This dust load should have shown up in the ice cores.
Where is that data? According to the traditions, the
fragments also set a large part of South America on
fire, which should have produced soot as well.
Sterling, do you have any ideas? Anyone?

good hunting,
EP

--- "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>
wrote:

> Hi, List,
>
> Yeah, here we go again...
>
> ----- Original Message -----
> From: "Marco Langbroek" <marco.langbroek_at_wanadoo.nl>
> >
> > Where? Where are the dust layers in peat deposits,
>
> > lake deposits, deep sea cores, ice cores from
> Greenland
> > and Antarctica for example? All there is, is a set
> of
> > narrow tree rings. No more.
> >
>
> It is necessary to examine the question
> quantitatively.
>
> Example: Earth encounters a very small globule
> of interstellar dust.
> It takes 36 days to traverse the globule. The dust
> that impinges on the
> Earth's atmosphere is accumulated in 36 days, during
> which solar flux
> to the ground is diminished by an arbitrary
> percentage, say 5%. Such
> varieties of dust are very fine, of small particle
> size. Most take years
> to fall out of the atmosphere.
> The original "strong signal" of the dust, with a
> 36 day duration,
> has now been "smeared out" to 6000 to 8000 days.
> Because
> the particles are very fine, they tend to
> incorporate themselves
> in surface layers, and erode away at the rate of
> general local
> erosion. Those particles that land on rock, sand,
> ice, move to
> soil or sea more quickly. The 6000 day smeared
> signal is smeared
> out to 50,000 days or more before that portion that
> reaches the sea
> or lakes is deposited there.
> Because the particles are "fines," they settle
> to the ocean bottom
> very slowly, 100,000 days or more. The mass "signal"
> is now
> down to about 10^-4 of its original strength. How
> much material
> is required to intercept 5% of the solar radiation
> and reflect
> or re-radiate it to space in the first place? The
> answer is a mere
> 1/2 gram per square meter if ice, more if it's
> silicate dust, less
> if the dust is "fluffy." Deposited at the sea bottom
> in a only
> 100,000 days, that's 5 MICROGRAMS per square meter
> per day, during which time it is being mixed with
> the much
> greater amount of normal terrestrial sediment being
> deposited.
> How detectable is that? If the material is
> particles from a comet
> that are mostly ICE, they degrade to WATER. Just how
> do you
> "detect" water? If the material is silicate dust,
> most of it is
> indistinguishable from any terrestrial silicate
> except for isotopic
> imbalances from the terrestrial ratios.
> When it's all settled we may be talking about
> "detectable"
> isotopes as low as one millionth of one millionth of
> a gram, or
> one femtogram! Maybe even 10 femtograms... Have you
> any
> concept of how difficult such a detection is? The
> German
> researcher who found the evidence of supernovae in
> sediments
> 2.2-2.3 million years old, namely Fe60, went through
> pounds
> of muck. He spent many years doing it. Know how much
> Fe60
> he found? SIX ATOMS! Then, everybody went out for a
> beer!
> [For those who wonder why this is definitive,
> there is no other
> place in the universe where Fe60 can be formed
> except in a
> supernovae. They can't be contamination from the
> lab, etc.,
> because there ain't any. Other supernovae-only
> isotopes are
> Be10 , Iodine 129 and Sm146. Find'em and you can go
> out for a beer, too! I'm buying.]
> You were expecting a Dust Bowl? Drifts
> accumulating
> in the streets? Having to wear a dust mask? Not
> really... The
> Earth already picks up some dust. There's argument
> about how
> much. Tens of thousands of tons per year? Hundreds
> of thousands
> of tons per year? So, how much do these tiny
> quantities of dust
> I've been talking about amount to? Only
> 2,500,000,000 tons!!!
> Yes, 2-1/2 BILLION tons. But it's only 1/2 gram per
> square meter.
> Imagine the tiniest pinch of talcum powder thrown up
> into the air
> and dispersed over more than a square yard! What
> would you see?
> Nothing much, if anything...
> So, you would never see the dust, only the
> suddenly and
> dramatically dimmed sunlight, the rapidly increasing
> cold, and
> all the rest of the litany -- only the disastrous
> effects would be
> perceptible.
> The Earth's area is a half billion square
> kilometers, so we're
> talking about 1/2 ton per square kilometer, the rate
> of mild
> organic fertilizer usage, or less lime than my yard
> needs to grow
> good grass again, or... you pick an example. It's
> not very
> much, but it's 'way too much, both at the same time.
> Some of the knowledgeable will jump in there
> and
> point out that the eruption of Tambora that produced
> the
> 1816 "year without summer" involved the injection of
> about
> 200 billion tons into the atmosphere! Well, two
> things count
> in causing climatic disaster: small particle size
> and high altitude,
> just what "cosmic" events provide and volcanoes do
> not.
> Tambora injected a coarse mixture of particles
> into the
> lower atmosphere of the northern hemisphere. Only
> the finest,
> highest particles persisted very long, perhaps 10 to
> 100 million
> tons, but it was they that dropped the temperature
> of the US briefly
> by 20 to 25 degrees C., to freezing in July and
> August. After a
> few weeks, temperatures rebounded to the 90's (F.).
> They were
> low and fell out quickly.
> A 5% reduction in solar flux would be much
> worse, probably
> worse than the 534 AD event hypothesized.
> So, that answers the "Where are the layers of
> dust?" question.
> Caveats and Weasels: The question of calculating
> the opacity
> of dust is really complicated. The physical
> parameters involved are:
> the particle cross sectional area; the mass opacity
> which is the area
> per gram of absorber; the absorption coefficient,
> which is the ratio
> of the area of absorber to its volume; if you're a
> chemist, the similar
> extinction coefficient; the "optical depth" (there's
> a formula for that;
> I got no symbols on this keyboard); and similarly
> the "transmittance."
> I looked up the values I could find; I (ahem)
> extrapolated the ones
> I couldn't. (This List is less fun than grad school,
> and it wasn't that
> much fun.)
> So, I could be off by a magnitude either way.
> This would not
> change the bottom line: the amount of fine dust at
> the top of the
> atmosphere sufficient to cause disaster would, if it
> fell down on you
> all at once, would hardly be noticed or at most be
> dusted off
> without a thought!
> If you like experiments: on a nice sunny day,
> construct and then
> stand in a 3 foot square black box 10 feet tall; put
> a three foot
> square pane of glass on the open top of the box;
> then have
> somebody dust it lightly with talcum powder until it
> forms a layer
> 1 millimeter thick; then look up. See much? (I'm one
> of those
> lowly physicists, not even an astro-, that Marco
> objects to;
> I like experiments.)
> See much?! you exclaim; it's about like night in
> here! Well,
> that's ten grams of dust per square meter at the top
> of your
> atmosphere.
>
> Sterling K. Webb
>
>
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
>
http://six.pairlist.net/mailman/listinfo/meteorite-list
>


__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
Received on Mon 24 Jul 2006 09:26:35 AM PDT