The problem of tektite origin.

["Louis Varricchio" <varricch@aero.und.edu>]

Hi!  Can anyone tell me who the author of this e-mail note is?  It appeared on our list a few weeks ago. Thanks!--Lou

—--------


The problem of tektite origin.


The origin of tektites was a subject of intense debate throughout
much of the 20th century owing to their unusual shape and their
chemical composition, which differs from glassy rocks of igneous
terrestrial origin. It was assumed that tektites formed from
the
molten ejecta of high-energy impacts, but the question remained
whether such impacts had taken place on the Earth or on the Moon
or elsewhere in space. Radioisotope measurements indicated that
tektites could not have originated from beyond the Earth-Moon
system but did not rule out a possible lunar origin. Under this
theory,
tektites were lunar rocks melted by the impact of meteorites
on the
Moon's surface. These tektites were thrown up into space, and
some of them eventually landed on the Earth. The lunar theory
was
most strongly supported by the distinctive lens-and-flange shape
of
australites, which suggested that they came from outside the
Earth's
atmosphere. The shape of these tektites could only be explained
by
two heating events; the first, which created the glass, and a
second
episode of heating apparently due to air-friction melting as
the
australite entered the Earth's atmosphere at a relatively high
velocity.
The lens-and-flange shape apparently results from a glassy sphere
melting on its forward side (the area of greatest friction);
as the
object slows down, some melt flows toward the lee and curls to
form a flange. (The same could happen, of course, to tektites
thrown outside the Earth's atmosphere which then underwent
aerodynamic heating in the course of their reentry.) 

The lunar-origin theory was advocated by a number of scientists,
but one important argument against it was the localized distribution
of tektites on the Earth. If tektites came from the Moon, their
distribution over the Earth's surface should be completely uniform,
which is certainly not the case. More importantly, the analysis
of
lunar rocks obtained by the Apollo space missions in the late
1960s
and early '70s showed that they were not suitable parent rocks
for
tektites, thus fatally weakening the lunar-origin theory. 

In support of tektites' terrestrial origin, it was long pointed
out that
the composition of tektites strongly resembles that of some rocks
that are widespread in the Earth's crust. It was only with the
emerging recognition of the links between impact craters with
some
strewn-field areas on Earth, however, that the theory of terrestrial
origin gained general support. The correlations between tektite
strewn-fields and terrestrial impact craters are numerous and
impressive. Ivory Coast tektites, for example, occur 300-1,600
km
(180-960 miles) from the Bosumtwi Crater in Ghana; and the
formation of both the tektites and the crater has been dated
at 1.3
million years ago. Similarities have been traced between the
crater
glass of Bosumtwi and the Ivory Coast tektites in chemical
composition, radioisotopic ratios, and other aspects. The same
similarities can be traced for several other impact craters and
their
associated tektite groups. The cumulative effect of this data
is
impressive, and a generic connection between craters and tektite
fields is now claimed by virtually all authorities.

-----
Sent using MailStart.com ( http://MailStart.Com/welcome.html )
The FREE way to access your mailbox via any web browser, anywhere!

LOUIS VARRICCHIO
 Environmental Information Specialist &
 Producer/Writer, "Our Changing Planet"
  (Visit OCP-TV on the Web at: www.umac.org/ocp)
  Upper Midwest Aerospace Consortium
  Odegard School of Aerospace Sciences
  University of North Dakota
  Grand Forks, N.D. 58202-9007
    Phone: 701-777-2482
    Fax: 701-777-2940
    E-mail: varricch@umac.org (in N.D.); morbius@together.net (in Vt.)

"Behind every man alive stand thirty ghosts, for that is the ratio by
which the dead outnumber the living. Since the dawn of time, a hundred
billion human beings have walked the planet Earth." -- Arthur C. Clarke

----------
Archives located at:
http://www.meteoritecentral.com/list_best.html

For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------

---

• Prev by Date: Correction
• Next by Date: A major assault on the famous Holbrook strewnfield !!
• Prev by thread: Impact Ejecta Exchange Between Planets
• Next by thread: Re: The problem of tektite origin.
• Index(es):
  • Date
  • Thread