[meteorite-list] THEORIES OF THE ORIGIN OF TEKTITES, Part Two
From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat Feb 18 01:55:30 2006
Part Two of
THEORIES OF THE ORIGIN OF TEKTITES
Passing through the Colossally Silly Entrance Hall, we next enter the
extensive and colorful Volcanic Tektite Exhibition.
5. The Terrestrial Volcanic Origin of Tektites: Mayer, in 1788, published
the first scientific tektite theory; he called moldavites "glassy lavas."
Charles Darwin, in 1844 (The Voyage of the H.M.S. Beagle), first described
australite "buttons" and identified them as obsidian. He wondered a great
deal about their unique shape, but became distracted by some issue or other
in biology, so the world lost a great tektite theorist.
The volcanic theory became as predominant in the 19th Century as the Impact
Theory is today. It was endorsed by Wickman, 1893; van Dijk, 1879; W. D.
Campbell, 1906; La Conte, 1902; and Moore, 1916 (who said tektites were
identical to "Pele's Tears"); Simpson , 1902, proposed Australite tektites
came from Krakatoa. Dunn, 1908 and 1912, proposed a complicated formation of
tektites inside of gas bubbles in fresh lava, a suggestion further developed
and complicated by Buddhue in 1940, while Dunn then later (1935) suggested
tektites were formed by rain and snow falling on molten lava.
The volcanic theories all died when geochemical analysis advances in the
20th Century, as tektites have a composition that is quite different from
any terrestrial volcanic rock, and tektites are easily distinguishable from
obsidian. It should be pointed out, in defense of Darwin and all the early
geologists, that just from the standpoint of holding a tektite and obsidian
in your hand and looking at them, they appear to be materially identical.
Chemical and physical analysis is required to distinguish them. It would
also appear that no one tried breaking a specimen of each, as the fracture
morphology of each differs.
However, the last Terrestrial Volcanic Theory was proposed in 1976! It is:
6. The "Cryptovolcanic" Origin of Tektites: McCall, 1976: To understand this
at all, we need to dig into the strange tribal relationships of science.
British geologists ("we invented geology, you know") were firmly wedded
(possibly even welded) to the volcanic origin of craters, all craters, of
all kinds, on all worlds. An immense amount of energy and thought had been
invested in lunar volcanic theory in particular, up through the 1950's.
Those who learned their geology at British institutions (Australians, New
Zedders, and so forth) were trained in this tradition. The notion of that
some craters on the Earth or elsewhere might have been formed by heavy
objects falling out of the sky was regarded as a crackpot theory put forward
entirely by brash and uninformed colonials of the American variety who were
well-known to be fond of whizz-bangs ("child-like, you know"), and the
impact theory was resolutely resisted as errant nonsense up until the moment
of the Moon landings, when it all unraveled in a snap.
A "volcanic" explanation was handy; there had always been craters from which
volcanic characteristics were absent. They were called by these geologists
"cryptovolcanic," meaning that their volcanic origins were hidden. This was
a theory built on the absence of evidence as a proof of the theory, always a
dangerous logical method. Cryptovolcanic craters were postulated to be the
result of direct venting of very deep, very hot, high pressure gassy magma
to the surface of the planet in a manner analogous to kimberlite pipes.
Advances of all kinds, but specifically in the ability to visualize deep
strata make "cryptovulcanism" a bad historical joke.
McCall, an Australian geologist and a good one, too, put forward a theory of
the cryptovolcanic origin of tektites in 1976. He also disbelieved in the
impact origin of terrestrial craters and of extra-terrestrial craters, lunar
craters, etc. This, in the post-Apollo era!
McCall was neither stupid nor uninformed and he fought a sharp rear-guard
action, to his credit. He was honest enough to point out that his own theory
was ruined by its inability to explain how you get tektites out of the
Earth's atmosphere (to then fall back) without ablating them up completely!
Leaving the Volcanic Tektite Exhibition Hall, we enter the spacious
Continued in Part Three...
Sterling K. Webb
Received on Sat 18 Feb 2006 01:55:23 AM PST