[meteorite-list] TEKTITE ORIGINS IN IMPACT?

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Sat Mar 26 11:08:45 2005
Message-ID: <424588E8.1FCBA7A1_at_bhil.com>

     

     THIS IS A (3nd) RE-POST OF EARLIER POST. I NEVER GOT A COPY BACK.
     IF IT'S A DUPLICATE FOR YOU -- THERE'S ALWAYS <DEL>

     Hi,

         Hey! If Rob says he can't figure out a way to get tektites
     shipped in from the Moon, it's good enough for me, But then, I
     never thought they came from the Moon. The lunar origin theory
     is an old one. In fact, all of the 40-odd theories of the origin
     of tektites are old (and most of them are odd, too).
         It might surprise meteorite fanciers to know that the
     argument over tektites goes back to the time when meteorites were
     still regarded as a myth or of being formed by thunder! The
     first speculation about tektite origins dates from 1793, more
     than a decade before the French Academy was persuaded by the
     L'Aigle fall that rocks really did fall from the sky.
         To those with long memories, I will recall to them the late
     List member Darryl Futrell, who supported the lunar origin
     theory, more from geological evidence than orbital
     considerations. I corresponded a lot with Darryl and I believe
     he did so more out of loyalty to the late John O'Keefe than being
     really convinced by the theory.
         Take a look at:
    
<http://six.pairlist.net/pipermail/meteorite-list/2001-May/024512.html>
    
<http://six.pairlist.net/pipermail/meteorite-list/2001-May/024513.html>
    
<http://six.pairlist.net/pipermail/meteorite-list/2001-March/022903.html>

         The current "orthodox" theory of tektite origin is the impact
     theory: that tektites are modified terrestrial surface rocks,
     modified by impact into molten drops, ejected into orbits above
     the atmosphere where they are rapidly cooled, which then re-enter
     the atmosphere at hypersonic velocities where they are re-heated
     and further modified in their descent to the surface of the
     Earth.
         It sounds perfectly reasonable. It powerfully explains the
     great variety of tektite shapes and many other characteristics of
     tektites, and the unique limited distributions of tektites. But
     there are problems -- huge problems -- with the theory. Here a
     few, for which there has never been any satisfactory answers.

         1. There are only four tektite-producing events in the past
     forty million years. (Maybe a few more, if you accept some odd
     single potential tektites, irghizites, and Lybian Desert Glass as
     tektites.) A giant question looms. Since there many, many
     impacts in the last forty million years, why did only four of
     them produce tektites?
         The answer is not size: Botsumtwi (source of ivorites) is a
     tiny crater.
         The answer is not perfect matches to craters: where is that
     giant australite-producing crater?
         All of the "big four" tektite-producing coincide with a
     reversal of the Earth's magnetic field. Why? And why only these
     impacts, and not the dozens of other?
         How are they different?

         2. If tektites are produced by earth impact, why do tektites
     contain no, not any, trace of terrestrial materials? That's
     right, boys and girls, there is no definitive trace of
     terrestrial origin in the composition of tektites. So how do you
     produce them from an earth impact without touching the earth?
         The quick ones among you will guess that they are made from
     the impacting body. Eergh! I'm sorry, wrong answer. They do
     not even vaguely resemble any extra-terrestrial material we know
     of. And the impact experts say that it's impossible anyway.
         If you plot the terrestrial surface compositions that matches
     the tektite bulk composition, the odds of four random impacts
     hitting only those spots on Earth are about 120 to one. Do you
     feel lucky?

         3. There are many oddities in the distribution of tektites,
     described as non elliptical geographically limited strewn
     fields. In the 1984 Shaw and Glassberg paper which is cited as
     the definitive proof of terrestrial origin (which it ain't), they
     cheerfully mention that one of the australites submitted for
     analysis (one that was recovered from the ocean off the
     australian coast), in not an australite at all. Nope, it's an
     ivorite.
         Now, the "source crater" for ivorites is almost exactly 180
     degrees in latitude and longitude from where this tektite was
     found, so either it is an "antipodal" tektite or it rolled along
     the ocean bottom for a million years and 15,000 miles without
     abrading!
         And then in 1988, Alan Hildebrand published his analysis of
     two "tektites" found in a Mayan Temple at Tikal -- they are
     australites, perfectly ordinary australites in every way. And
     yes, Tikal is almost exactly 180 degrees in latitude and
     longitude from Australia.
         So did they crawl off Australia, cross the Pacific, climb up
     on the land and travel hundreds of miles across Guatemala to get
     to where the Mayan temple would be built in 793,000 years? Or
     did they fall from the sky and survive until they were brought to
     the priests as the mystery that they were (and are)? And if two
     tektites were brought to Tikal, wouldn't you guess a lot more
     than two fell?
         So, two of the four tektite fields are global, not limited in
     distribution. (The antipodal points for the other two craters are
     in deep ocean, S. Pacific and S. Indian.)

         It gets worse. There is no one impact theory. There is
     absolutely no agreement as to what the production mechanism is.
     Everyone supporting "impact" puts forward differing (and
     contradictory) mechanisms.
         The majority of impactists say surface jetting is the source
     of tektites, even though jetting in theoretical models of impact
     occurs from the body of the impactor rather than from the target
     material. This would be fine if they proposed silica impactors,
     but they emphatically do not. A large number of geochemists point
     to surface deposits as the only possible source for a tektite
     composition. The question is, why doesn't this happen with all
     (or most) impact events?
        Wasson's "atmospheric cratering event" proposes that there are
     no craters created in tektite producing events, which is curious
     when you consider the "coincidence" of nearby impact craters of
     tektite matching dates, like Botsumtwi, the Ries Kessel, and the
     Chesapeake Bay structure. I like most aspects of this explanation
     except for those inconvenient craters. (Perhaps these are twin or
     multiple impacts, asteroids with satellites, one of which
     atmospherically craters?) Another problem is the sheer volume of
     tektite material. The North American strewn field is estimated at
     0.5 to 13 billion tons of tektites; that would require one hell
     of an excavation.
         Jay Melosh, the chief theorist of impact events in general,
     says it is impossible to produce tektites by jetting. He proposes
     that they form from deep rock below the crater on rebound
     decompression. But the associated craters show no evidence of any
     deeper excavation than non-tektite craters, and deep rock sources
     are compositionally unlikely. And, again, why doesn't this happen
     with every crater?
         Guy Heinen proposes another kind of jetting of unknown
     mechanism that occurs only in glancing, low incidence impact, but
     nothing about these three craters supports a low (5 to 10
     degrees) angle of incidence -- they're not ovals, and they don't
     have one rim wall elevated over the rest of the crater, and so
     forth.
         All these proposals are hand-crafted fudge mechanisms,
     created not to reflect any known characteristic of tektite
     producing impacts but to produce a model tailored to avoid any
     contact of target material with the material of the impactor.
     This is necessary because tektite material is pretty much free of
     any "fingerprints" of an impactor.
         Let's face it; it's really hard to impact something without
     touching it! It's a really obvious problem for the impact
     theories. A problem for which there are, again, no answers.
         Surface jetting theories have yet another problem. A little
     simple geometry shows that a surficial jet would have to escape
     by the time the impactor has penetrated about its own radius into
     the crust (that's the point when it vaporizes). To do so, a test
     particle of a forming jet would have to travel a distance of
     about one-quarter of the circumference of the impactor in that
     time. This would give it an exit velocity of more than three
     times the velocity of the impactor! Since big impactors have
     velocities near Earth's escape velocity when they hit, the jet
     would have to greatly exceed escape velocity. How would that
     produce tektites, which must have sub-orbital velocities in order
     to return to Earth?
         Digging into the literature of tektite-from-impact theory, I
     keep looking for three little words, the three little words that
     if they could be explained away would quiet my skepticism about
     impact theories: Rayleigh Taylor Instability.
         What the hell is that? Here's an everyday example. Picture a
     flag in a very slow but steady breeze; it stands straight out
     parallel to the flow of air. Increase the wind speed very
     slightly and the flag begins to wave back and forth; those are
     Rayleigh Taylor waves. Increase the wind a little bit more and
     the flag waves faster and faster. In a 25 mph wind, the waves
     become very rapid and chaotic; the flag is fluttering so fast
     it's a blur and the fabric begins to snap and pop. At 35 to 40
     mph, the fabric starts to shred itself because the propagation
     velocity of the Rayleigh Taylor waves has exceeded the speed of
     sound by the time they reach the trailing edge.
         Note that driving force (wind) is very moderate, but the
     Rayleigh Taylor waves increase in intensity in a violently
     explosive way. No increase in velocity, pressure, density, or
     temperature can suppress Rayleigh Taylor instability, which is
     why it is the chief difficulty in designing a good working
     boosted fusion device, i.e., the hydrogen bomb. Just trot up the
     road to Los Alamos and ask'em.
         Take my word for it, there is no way around Rayleigh Taylor
     instability in an impact mechanism.
         Rayleigh Taylor instability guarantees a thorough mixing of
     impactor and target material if they get close enough to interact
     with one another. Going the route of the Wasson and Melosh
     variants only makes the problem worse. If the target material
     is vaporized, so is the impactor material, and segregating a
     gas phase is a lot harder (really, more impossible, if you can
     say that) than segregating a liquid phase. And Rayleigh Taylor
     instability applies just the same (even in a plasma phase), in
     fact, it gets worse the more energetic the event. In other
     words, theories of impact all have this fatal flaw.
         There's no problem getting tektites blown out of the
     atmosphere by an impact; the problem is forming them in the
     first place. Actually, a silica impactor answers most of the
     difficult questions, but nobody seems to believe in one, probably
     due to the complete absence of any smaller examples of this
     composition (no silica meteorites that we know of).
         There are plenty of other questions.
         Why should only a few impact events produce tektites, out of
     all the impact events of the last 40 million years? Bigger
     impactors? (No evidence.) Faster impactors? (No evidence.)
     Cometary impactors (No evidence.) One unique surface composition?
     (Conflicting evidence.)
         Why are there no detectable characteristics of tektite
     associated craters that distinguish them from non-tektite
     producing craters?
         Why does it take a huge crater like Chesapeake to produce the
     North American tektites, when the rather puny Botsumtwi crater
     blasts tektites all over the Atlantic? (Note: an Ivory Coast
     composition tektite was recovered off the NE Australian coast;
     this is literally halfway around the planet, so maybe I should
     have said "all over the world.")
         Where is the crater for the Australasian tektites?
         Why are the "big four" tektite producing events associated
     with reversals in the polarity of the Earth's magnetic field? (We
     don't even know why the field reverses, as far as that goes.)
     Another coincidence"?
         The "impact solution" just doesn't come together for me. If
     it were a coherent set of ideas, if there were a plausible
     mechanism, if the theories had implications that were testable,
     if the theories didn't exclude each other, they'd be a lot more
     convincing.
         I carry no brief for lunar origin nor any other of the 30-odd
     other theories. I just don't know, which leaves me free to
     hypothesize.
         Then, there's the missing crater for the australite-producing
     event which just happened yesterday in geological terms. Where
     is it? People keep proposing candidate craters but it never
     holds up.
         Glass and Pizzuto (1994) estimated the diameter of the impact
     crater to be between 32 and 114 kilometers. They made no assertions
     about the impactor's characteristics. If it was a stony asteroid
     traveling at a speed of 22 km/s then its diameter would be
     between 2 and 5 km.
         The notion that an impact of this magnitude could have
     occurred only 800,000 years ago without leaving detectable
     evidence behind is, well, ridiculous. So, I drug out my copy
     of Gehrels' Hazards Due to Comets and Asteroids and Glasstone's
     Effects of Nuclear Weapons (scaling up) and started listing the
     consequences of a 5 kilometer impactor with a crater of 90 to 110
     kilometers.
         A) It would mass in at about 200,000,000,000 tons.
         B) The impact energy would be the equivalent of
     10,000,000,000,000 tons of TNT. (Picture a full exchange of
     all the nuclear weapons of all the nuclear powers all on one
     spot all at one time. Multiply by a factor of 2000. Apply a
     lot of sunblock.)
         C) The area of total devastation would be roughly
     large-nation-sized (like about the size of Mexico).
         D) The energy release would be just at the lower threshold of
     a major mass extinction event.
         E) It would be the biggest impact since the dinosaur-killer
     itself.
         F) If it missed continental crust and hit the ocean (the
     favorite excuse for the absence of a crater), the resulting
     tsunami would have had a wave height of roughly 1000 meters!
         G) The other characteristic we asked to believe about this
     supposed tektite forming event is that it happened very recently
     and that it left virtually no mark on the planet.
         It reveals the intellectual poverty of impact dogma to
     require an impact of this magnitude to create the Australasian
     field and be unable to find any trace of that fresh hole --- 70
     miles across and 12,000 to 20,000 feet deep --- in Indochina or
     anywhere else. You can't bury all traces of a crater 1/3 the size
     of Chicxulub in less than a million years. (Simple arithmetic: it
     would take depositation of 1-2 meters of sediment per century to
     fill the damn thing in and bury it in so short a time, but that
     would hardly hide it.)

         Can I say it? Gimme a break!

         If tektites were produced by large impacts, there would be a
     stochastic distribution of ejecta sizes and ejection velocities,
     maybe not Gaussian (ye olde Bell Curve), but some small portion
     -- 2% to 10% -- of the billion of tektites would have been
     ejected at or above escape velocity. These would end up in near
     Earth orbits and eventually 50% to 80% of them would be swept
     back up by the Earth in 10,000 to 1,000,000 years.
         The result would be random distribution of isolated tektites
     of varying types all over the Earth with CRE dates up into the
     millions of years. Since tektites number in the millions and
     millions at the very least, there would be enough objects in this
     class to have been found this way. (They should out-number Mars
     rocks by thousands to one, and they should be falling all the
     time.) Again, this situation does not seem to occur. Why not?

         On the other hand, the traditional notion of the tight
     limited strewn field for tektites is also suspect. (See #3
     above.)
         Now, if somebody could only find a moldavite in Antarctica...
     Who knows, maybe they will!
         Does this mean that the "strewn fields" really cover the
     whole planet? Does that argue for a lunar origin? Does it argue
     for a large impact origin? Does it mean something else
     altogether?

         There are plenty of other questions.
         Why should only a few impact events produce tektites, out of
     all the impact events of the last 40 million years? Bigger
     impactors? (No evidence.) Faster impactors? (No evidence.)
     Cometary impactors (No evidence.) One unique surface composition?
     (Conflicting evidence but another big fat coincidence if true.)
         Why are there no detectable characteristics of tektite
     associated craters that distinguish them from non-tektite
     producing craters?

         Why does it take a huge crater like Chesapeake to produce the
     North American tektites, when the rather puny Botsumtwi crater
     blasts tektites all over the Altantic and apparently all the
     way to Australia?
         Why are the "big four" tektite producing events associated
     with reversals in the polarity of the Earth's magnetic field? (We
     don't even know why the field reverses, as far as that goes.)
     Another "coincidence"?

         Actually, an impactor that is already nearly a tektite in
     composition, a high silica impactor, answers some of the
     difficult questions, but nobody seems to believe in one, probably
     due to the complete absence of any smaller examples of this
     composition (no silica meteorites that we know of). But this
     smacks of an ad hoc approach, creating a hypothetical unique
     object to explain an unique unexplained event.
         Actually, the renowned Alfred Kroeber published a paper that
     made that suggestion. The notion sank like a rock in the
     ocean...

         Conversion of a true mineral (possessing crystals) into a
     glass (amorphous liquid) is probably the best way of concealing
     the original composition of any natural substance ever devised.
     God is tricky sometimes. He probably left lots of clues, but
     so far, I think we've overlooked some of them.


     Sterling Webb
Received on Sat 26 Mar 2005 11:08:08 AM PST