PLEASE NOTE:
*
CCNet, 12 November 1999
------------------------------
POEM OF THE DAY
By Malcolm Miller
stellar2@actonline.com.au
LEONIDS
Speeding specks of unknown stuff might
light the sky,
diverging in silent lines, some short,
some long,
across clear skies in thousands,
spectacular beyond belief
when at their best. In quieter years,
those in the know
huddle warm wrapped, eyes on the sky,
seeing what happens
when velocity's vast energy's converted
into heat.
Perhaps their greatest lesson is that
space is hazardous,
it has its storms and reefs as well as
any ocean,
the shoals and rocks of space that every
navigator
must heed to come safe home from
voyaging.
Six hundred tiny vessels circle
endlessly this island Earth,
as vital to our trade as any caravel of
Spain in ages past;
it may be that a few will founder in the
Leonids brief hurricane,
but from their loss we'll learn to make
our space ships safer.
MM 12.11.99
(1) 200 POTENTIALLY HAZARDOUS ASTEROIDS
http://cfa-www.harvard.edu/cfa/ps/pressinfo/200PHAs.html
(2) LEONIDS: RAPID INFORMATION DISSEMINATION
Marc Gyssens <gyssens@charlie.luc.ac.be>
(3) COMPACTION AS THE ORIGIN OF THE UNUSUAL CRATERS ON MATHILDE
NATURE, 11 November 1999
(4) NEW SCALE FOR IMPROVED SPACE WEATHER PREDICTION
Andrew Yee <ayee@nova.astro.utoronto.ca>
(5) IMPACT DIAMONDS IN A FENNOSCANDIAN CRATER
F. Langenhorst et al., UNIVERSITY OF BAYREUTH
(6) CLIMATE CATASTROPHES
M. Budyko, STATE HYDROL. INSTITUTE, ST
PETERSBURG
(7) DOES LIFE'S HANDEDNESS SPRING FROM WITHIN?
Andrew Yee <ayee@nova.astro.utoronto.ca>
==========
(1) 200 POTENTIALLY HAZARDOUS ASTEROIDS
From <http://cfa-www.harvard.edu/cfa/ps/pressinfo/200PHAs.html>
PRESS INFORMATION SHEET: Produced at the Harvard-Smithsonian
Center for
Astrophysics (CfA), Cambridge, Massachusetts, U.S.A.
Today saw the announcement of the discovery of the two-hundredth
PHA,
or "potentially hazardous asteroid". This milestone was
reached with
1999 VP11, found on Nov. 7 by LINEAR, the Massachusetts Institute
of
Techology's Lincoln Laboratory Near-Earth Asteroid Research
project. In
less than three years this project has yielded more than
one-third of
all the PHAs, which are asteroids that can pass within 0.05
astronomical unit (5 million miles) of the earth and are
intrinsically
brighter than absolute magnitude 22 (suggesting that they are
more than
about 600 feet across).. The first PHA, known as Apollo, was
discovered
in 1932, and all but 15 of the PHAs have been found during the
past 20
years. Just half of the PHAs have been discovered since the
middle of
1997, with the recent LINEAR contribution supplemented by the
University of Arizona's longstanding Spacewatch project, with 12
discoveries; the Near-Earth Asteroid Tracking program of the Jet
Propulsion Laboratory, with six discoveries; the University of
Arizona's Catalina Sky Survey, with five; and the Lowell
Observatory
Near-Earth Object Program, with four. The Arizona amateur
astronomer
Roy Tucker has discovered two PHAs.
Mere categorization as a PHA does not imply that an object will
pose
any danger to the earth during the next tens of millennia and
more, but
this is a convenient subset of the more inclusive collection of
Near-Earth Objects, most of which actually come nowhere near the
earth.
More than 40-percent of the PHAs have been so extensively
observed that
there is no way more than one or two of these could conceivably
be a
threat a half-millennium, say, from now. For another 30 or 40
percent
the minimum distances between their orbits and that of the earth
are
currently too large for there to be any real possibility of an
impact
within the next half-millennium. Only a fraction warrant any
serious
examination for a possible impact during the next half-century or
so.
And that examination is now routinely occurring, thanks mainly to
the
efforts of the group at the University of Pisa. The number of
actual
cases found where there has been any conceivable danger during
the next
half century is remarkably small--four objects altogether.
Knowing of
these cases in a timely manner then allows special observational
efforts to be made, including the search for images of these
bodies in
the old photographic archives. It should be no surprise that
further
observations will eliminate these possible dangers--almost all of
the
time... At least for the intrinsically brighter objects, which
include
those half a mile across and larger, and thanks to the dedication
of an
ever-increasing set of observers, professional and amateur, the
process
is working just fine.
Brian G. Marsden
1999 November 11
E-mail: bmarsden@cfa.harvard.edu
=============
(2) LEONIDS: RAPID INFORMATION DISSEMINATION
From Marc Gyssens <gyssens@charlie.luc.ac.be>
I N T E R N A T I O N A L M E T E O R O R
G A N I Z A T I O N
1999 Leonids: Rapid Information Dissemination
---------------------------------------------
Dear meteor observer,
From earlier communications, you have learned that the IMO is
setting
up a communication network to obtain reliable information as soon
as
possible after the event in the morning of November 18. We invite
you
to contribute to this effort.
First of all, we want to point out you must DISTINGUISH between
the
USUAL OBSERVATIONAL REPORTS, such as collected by the IMO's
Visual
Commission, and which may be used for detailed, global analyses,
and
the "EXPRESS REPORT" described below which serves as
sole purpose the
compilation of a rough but reliable picture of the activity
within
hours after the event.
The EXPRESS REPORT should have the following format:
Meteo R. Observer
Fireball City (45N 10E)
Time Interval (UT) Lim. Magn.
Nr. of Leonids Remarks (if any)
-----------------------------------------------------------------------
01:15-01:30
5.8
27
None
01:30-01:45
5.9
56
None
01:45-02:00
6.1
156
None
.
.
.
To the extent possible, bin your observations for this
"express report"
in time interval of 15 MINUTES.
(Again, the full report of your observations will be different
from
this express report, as shorter intervals are required as well as
magnitude distributions and some additional data - see the
earlier
posted article with visual observing hints - but the above data
suffice for the purpose indicated.)
If you wish to collaborate with the IMO in this respect, please
send
your express report for the night of November 17/18 ONLY (or, of
course,
for any unexpected activity you might happen to witness)
*** IMMEDIATELY AFTER THE OBSERVATION *** to the following email
addresses:
wgn@imo.net
gyssens@hcoss.uia.ac.be
The latter is a back-up address in case Web-site access to www.imo.net
would prove to slow down our computer too much. This back-up
address
will be active only on November 17 and 18!
Thank you in advance for any collaboration we may receive!
Marc Gyssens
International Meteor Organization
=============
(3) COMPACTION AS THE ORIGIN OF THE UNUSUAL CRATERS ON MATHILDE
From NATURE, 11 November 1999
http://www.nature.com/server-java/Propub/nature/402155A0.abs_frameset
Compaction as the origin of the unusual craters on the asteroid
Mathilde
KEVIN R. HOUSEN, KEITH A. HOLSAPPLE & MICHAEL E. VOSS
The asteroid Mathilde has suffered at least five giant impacts.
Previous studies suggest that Mathilde's giant craters should be
surrounded by blankets of ejecta that are kilometres deep, yet
the
craters show no evidence of filling by material excavated during
later
nearby impacts. Computer simulations of impacts have been used to
suggest that the absence of ejecta arises because the impact
energy is
deposited in a small volume, due to Mathilde's unusually high
porosity,
which produces ejecta velocities so high that nearly all of the
material escapes Mathilde's gravitational field. Here we report
laboratory measurements of high-velocity impacts into porous
material,
which support an alternative explanation: the crater is formed
mainly
by compaction, not excavation. The small amount of ejecta lofted
in our
experiments have velocities sufficiently low that nearly all of
the
material is redeposited within the crater bowl. The crater itself
results from material being compressed, rather than ejected. This
type
of cratering implies that highly porous asteroids are minor
contributors of meteorites, because essentially no material
escapes
the asteroids. Nature © Macmillan Publishers Ltd 1999 Registered
No.
785998
=============
(4) NEW SCALE FOR IMPROVED SPACE WEATHER PREDICTION
From Andrew Yee <ayee@nova.astro.utoronto.ca>
NOAA
Contact: Barbara McGehan
NEW NOAA SPACE WEATHER SCALES MAKE SOLAR MAX EFFECTS MORE
PREDICTABLE
As the sun revs up for Solar Max, a time of intense solar
activity, we
can look forward to increasingly turbulent space weather. Today
the
National Oceanic and Atmospheric Administration introduced the
first-ever scales designed to characterize the severity and
impact of
upcoming solar storms on public safety and services.
"NOAA's new scales are the Richter scales of space weather.
For the
first time, we can predict the impact of solar storms, and these
storms
may be a real Y2K problem," said Dr. D. James Baker, under
secretary
for oceans and atmosphere and NOAA administrator. "When
Solar Maximum
occurs, the sun bursts at its seams with explosive power, and as
it
churns there is potential for electrical power outages, radio
problems,
and the disabling of satellites. This can disrupt communications,
including broadcast transmissions and pagers," Baker said.
As the period during the 11-year solar cycle when the sun is most
active, Solar Maximum brings an increase in the number and
intensity of
solar storms and their effects. Space storms, radiation showers,
aurora
borealis, and affects on power grids and Global Positioning
System
navigation and other systems are all expected during the upcoming
Solar
Max period, which is expected to last about three years.
Already there is an increase in solar activity as the world
approaches
another Solar Maximum. As we get farther into Solar Cycle 23,
expectations are that the sun will continue to rev up. Each time
there
is a solar event, NOAA's National Weather Service includes
information
on the event in its transmission of weather data.
Working like the Richter scale for earthquakes, NOAA's new space
weather scales describe the intensity and frequency of three
kinds of
solar events: geomagnetic storms, solar radiation storms and
radio
blackouts. "The scales are a giant step forward in informing
the public
about the severity of these events and their expected
consequences,"
said Dr. Ernie Hildner, director of NOAA's Space Environment
Center in
Boulder, Colorado. Hildner said that physical measurements on the
scales will help the scientific and operations communities
consistently
identify the intensity of solar events. Solar storms can vary,
with
some equivalent to a thunderstorm on Earth, while others may be
more
severe, with intensity similar to a hurricane or tornado.
Satellite expert David Desrocher, a senior engineer at The
Aerospace
Corporation in Colorado Springs, Colorado, said that,
"NOAA's new space
weather scales will significantly aid the space industry in
anticipating events, understanding effects, and developing more
robust
satellite designs and mitigation strategies." John
Kappenman, a senior
engineer at Metatech in Duluth, Minn., explained that space
storms can
impact the operational reliability of electrical transmission
systems
world-wide. "The previous solar cycle demonstrated just how
seriously
the power industry needs to consider the potential impacts of
geomagnetic storms," Kappenman said.
One of the strongest impacts occurred during the last solar cycle
in
1989, when the entire Province of Quebec went dark because a
geomagnetic storm caused power lines to overload.
NOAA's Space Environment Center in Boulder is responsible for
issuing
warnings, watches and forecasts of the space environment and
potential
impacts on Earth. The Center continuously monitors the solar
environment with a complex array of ground-based observations and
satellites operated by NOAA and its national and international
partners.
For more information on the Space Environment Center, check out
www.spaceweather.noaa.gov
For a comprehensive list of charts and graphics see the following
page:
http://www.sec.noaa.gov/info/Media/
=============
(5) IMPACT DIAMONDS IN A FENNOSCANDIAN CRATER
F. Langenhorst*), G.I. Shafranovsky, V.L. Masaitis, M. Koivisto:
Discovery of impact diamonds in a Fennoscandian crater and
evidence for
their genesis by solid-state transformation . GEOLOGY, 1999,
Vol.27,
No.8, pp.747-750
*) UNIVERSITY OF BAYREUTH,BAYER GEOINST,POB 101251,D-95440
BAYREUTH,GERMANY
We report here the first discovery of impact diamonds on the
Fennoscandian shield, in the deeply eroded Lappajarvi impact
structure,
Finland. The tabular morphology and microstructural twin bands
provide
evidence for the solid-state transformation of graphite to form
these
diamonds within <1 s. Strong corrosion and coating of surfaces
with
amorphous carbon may result from the thermal interaction of the
diamonds with enclosing impact melt. Because of their unique
characteristics, impact diamonds can be easily distinguished from
kimberlitic diamonds, in general. Durable impact diamonds may
thus
serve as indicators of ancient impact horizons that could mark
biological and climatic catastrophes in Earth's history.
Copyright
1999, Institute for Scientific Information Inc.
===============
(6) CLIMATE CATASTROPHES
M. Budyko: Climate catastrophes. GLOBAL AND PLANETARY CHANGE,
1999,
Vol.20, No.4, pp.281-288
STATE HYDROL. INSTITUTE,23 2ND LINE,ST PETERSBURG 199053,RUSSIA
Climate catastrophes, which many times occurred in the geological
past,
caused the extinction of large or small populations of animals
and
plants. Changes in the terrestrial and marine biota caused by the
catastrophic climate changes undoubtedly resulted in considerable
fluctuations in global carbon cycle and atmospheric gas
composition.
Primarily, carbon dioxide and other greenhouse gas contents were
affected. The study of these catastrophes allows a conclusion
that
climate system is very sensitive to relatively small changes in
climate-forcing factors (transparency of the atmosphere, changes
in
large glaciations, etc.). It is important to take this conclusion
into
account while estimating the possible consequences of now
occurring
anthropogenic warming caused by the increase in greenhouse gas
concentration in the atmosphere. (C) 1999 Elsevier Science B.V.
All
rights reserved.
===========
(7) DOES LIFE'S HANDEDNESS SPRING FROM WITHIN?
From Andrew Yee <ayee@nova.astro.utoronto.ca>
[http://www.academicpress.com/inscight/11111999/graphb.htm]
Thursday, 11 November 1999, 5 pm PST
Does Life's Handedness Spring From Within?
By Robert F. Service
Although amino acids and other molecules essential to life come
in two
mirror-image versions, like a right and a left hand, biology
without
fail grabs one and shuns the other. This bias has puzzled
researchers
for decades. But at the International Symposium on Cluster and
Nanostructure Interfaces in Richmond, Virginia, on 27 October,
scientists reported preliminary findings indicating that the
source of
the bias might lie in the heart of molecules themselves -- in the
so-called weak force that operates within the nuclei of atoms.
For decades, researchers have searched for a phenomenon --
astronomical, electromagnetic, or nuclear -- that could have
imprinted
this handedness, or chirality, on nature. One candidate, the weak
nuclear force, governs the radioactive decay of a neutron into a
proton
and an electron, and the force has a handedness: The decay always
produces an electron with a left-handed spin. Because the weak
nuclear
force is the only chiral fundamental force in nature, it was
tempting
to link it to the handedness of biomolecules. But proof was
lacking.
At least that's the way things stood before chemical physicist
Robert
Compton of the University of Tennessee, Knoxville, and colleagues
turned their hands to sodium chlorate. This salt forms crystals
made of
atoms arranged in either a clockwise or counterclockwise spiral.
Environmental factors, such as stirring, can influence the
direction of
those spirals. Compton and his colleagues wondered if lefty
electrons
produced by radioactive decay could produce the same effect.
They weren't disappointed. When the researchers bombarded a
solution of
sodium chlorate with left-spinning electrons from radioactive
strontium, they wound up with an excess of right-handed crystals.
And
when they hit the solution with positrons -- positively charged
counterparts to electrons, which have the opposite spin -- an
excess of
left-handed crystals formed.
"It's a very, very interesting experiment," says Roger
Hegstrom, a
chemist at Wake Forest University in Winston-Salem, North
Carolina. It
doesn't prove that the weak nuclear force is responsible for
biology's
handedness, he says, but it's an important step in that
direction.
© 1999 The American Association for the Advancement of Science
[Extracted from INSCiGHT, Academic Press.]
----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To
subscribe/unsubscribe,
please contact the moderator Benny J Peiser <b.j.peiser@livjm.ac.uk>.
Information circulated on this network is for scholarly and
educational use only. The attached information may not be copied
or
reproduced for any other purposes without prior permission of the
copyright holders. The fully indexed archive of the CCNet, from
February 1997 on, can be found at http://abob.libs.uga.edu/bobk/cccmenu.html
*
LETTERS TO THE MODERATOR - CCNet, 12 November 1999
--------------------------------------------------
(1) FLUFFY ASTEROIDS SHOULD BE EASIER TO SHOVE AROUND
Roy Tucker <tucker@noao.edu>
(2) ONE OTHER DOWN SIDE OF THE TORINO SCALE
Mark Kidger <mrk@ll.iac.es>
(3) DUST VEILS & THEIR CLIMATIC EFFECTS
Doug J Keenan <DJ.Keenan@virgin.net>
(4) MORE DETAIL NEEDED ON COMETARY DUST LOADING
Roy Tucker <tucker@noao.edu>
(5) CHICXULUB IMPACT & THE DECCAN TRAPS
Oliver Morton <abq72@pop.dial.pipex.com>
(6) K-T BOUNDARY IMPACT-VOLCANIC CONNECTION?
Andrew Glikson <andrew.glikson@anu.edu.au>
(7) ANOTHER SCI-FI FABLE
Stephen Ashworth <sa@astronist.demon.co.uk>
==========
(1) FLUFFY ASTEROIDS SHOULD BE EASIER TO SHOVE AROUND
From Roy Tucker <tucker@noao.edu>
At 09:59 AM 11/11/99 -0500, it was written in CCNet:
>Crushable Asteroids May Absorb
Impacts
>By Robert Irion
>Asphaug notes that such objects,
which he calls "flying Rice
>Krispie treats," might swallow
projectiles without breaking apart
>or significantly changing their
orbits. That's potentially bad
>news, Asphaug and Housen agree, if
one of those rubble piles
>takes dead aim at Earth: The
menacing asteroid might just shrug
>off efforts to deflect it.
Dear Dr. Peiser,
I'm puzzled. The deflection of an asteroid or comet is a variety
of
inelastic collision. The primary considerations are the force
applied
to the body and the total mass of the body. Given a choice
between
being threatened by an asteroid made of light, fluffy stuff or
solid
platinum-group metals, I would conclude that, for similar sized
bodies,
the styrofoam asteroid should be easier to shove around. If the
objective was to disrupt a body, I would still prefer the
styrofoam.
Am I missing something?
Best regards,
- Roy Tucker
=================
(2) ONE OTHER DOWN SIDE OF THE TORINO SCALE
From Mark Kidger <mrk@ll.iac.es>
Dear Benny:
I have followed the debate on the Torino Scale with some
interest. Not
having a vested interest in the issue as I only do a little work
on
NEOs, I feel that I can look at it a little as an outsider would.
My first impression was of an analogy to the Richter scale. If
something is up there 6, 7, 8 you pay attention, and quickly!
Whoever
though reported a Richter 1 or 2 earthquake on the tv news?
One of the oddities of the Torino scale is precisely the fact
that it
is extremely difficult for an event to get above 1. Now that may
well
be a good thing. Assuming that the media will only start to take
an
interest as that number creeps up, and that a 2 or a 3 will be a
very
very rare event, we can be quite sure that there would almost
certainly
be no media interest in a possible impact during the rest of my
career.
We certainly avoid any more 1997 XF11 or 1999 AN10 events. That
would
allow serious investigation of the object before the media start
to
take an interest.
There is however a down side and it needs to be carefully
balanced. The
first thing is that if objects only rarely even start to register
on
the scale with a "1", there are two effects. One is a
public perception
that the problem has suddenly "gone away": I don't hear
about it any
longer, ergo it does not exist. The truth is that the problem
still
exists, will not go away, and can only get more serious if a
reduced
public profile of the issue leads to a serious reduction in
funding for
NEO programs. The second is that the scientific interest to
follow-up
interesting cases will sharply reduce. Scientists do have to
justify
their funding, they do need public interest; if it does not exist
they
will move on to a topic that does offer such scope. This could
lead to
a serious reduction in follow-up of cases perceived to be
"low risk".
If people thing that this is silly alarmism, remember that it was
only
due to the efforts of a Japanese amateur that 1997 XF11 was not
lost
almost immediately after discovery - for whatever reason there
was no
immediate professional follow-up.
My doubt is thus with a scale that will almost always be used at
the
"0" or "1" level meaning that there is no
significant danger. Torino
has a wonderful system for categorising "the big one"
but, for the
general public, whether an object receives a "5" or an
"8" will
probably only influence the level of panic generated.
If I were to suggest a modification, it would be to expand the
lower
end of the scale in a similar way to the Richter scale: 0-3 ...
normal,
no real danger; 4-5 ... worth watching, but not too serious; 6
and up,
ever increasing serious danger. But do things in such a way that
objects that register 2-3 on the scale are relatively frequent
(maybe 1
to 2 per year) and that a "4" may happen every few
years, "5"s though
should be infrequent and larger numbers very rare indeed.
However, we
would avoid a public perception that there is no problem simply
because
the scale does not easily start to move.
Mark Kidger
=================
(3) DUST VEILS & THEIR CLIMATIC EFFECTS
From Doug J Keenan <DJ.Keenan@virgin.net>
Benny,
Yesterday's posting by Roy Tucker assumed that the climatic
after-effects of an eruption are largely determined by the mass
loading
of the atmosphere. This is false. The climatic after-effects are
largely determined by the sulfur mass loading of the
stratosphere. For
an elaboration, see item 34 at
http://climate.envsci.rutgers.edu/robock/robock_volpapers.html
Roy Tucker's calculated upper-bound of 10^16 g of cosmic dust is
orders
of magnitude larger than the sulfur mass loading of the
stratosphere by
Tambora in 1815--which induced severe climatic
after-effects. Hence the
calculation does not show that cosmic dust cannot affect climate.
To get an idea of how sensitive Earth's climate system can be to
changes in received solar radiation, consider that the total
energy
fluctuations over the 11-year solar cycle are <0.1%, and yet
these
fluctuations are believed to significantly impact global climate
[e.g.
J. D. Haigh, Science, 1996].
Cheers,
Doug Keenan
http://freespace.virgin.net/doug.keenan
============
(4) MORE DETAIL NEEDED ON COMETARY DUST LOADING
From Roy Tucker <tucker@noao.edu>
Dear Dr. Keenan,
My letter to CCNet indicated more detail was necessary which has
now
been provided. The primary climate modification mechanism
proposed is
the introduction of sulphur into the atmosphere, not just the
increased
opacity due to dust. C1 carbonaceous chondrites have an average
sulphur
content of 5.9% which would suggest that my model event would
introduce
about 6x10^14 grams of sulphur. Since the yearly average volcanic
production of sulphur is about 1.3x10^13 grams
(http://blueskies.sprl.umich.edu/geia/emits/volcano.html)
the
environmental consequence would indeed be significant. The
eruption of
Tambora produced about 6x10^13 grams of sulphur
(http://volcano.cs.und.nodak.edu/vwdocs/Gases/eruptions.html).
The figure of 7.4 cubic kilometers was intended as an extreme
example
and assumes the entire cometary nucleus was disrupted and
uniformly
dispersed into a lunar orbit-sized coma. You'll agree that this
is an
implausible scenario. The questions then are what is a more
reasonable
number for the dust density in the coma of a comet (my value of 2
x
10^13 grams/cubic cm was a typo, of course. That should be
10^-13) and
how often will the earth pass through a cometary coma? I must
defer
these questions to someone more familiar with these numbers than
I.
If indeed the passage of the earth through a cometary coma can
produce
some environmental consequence, how does the magnitude and
frequency of
such events compare to those due to volcanic activity?
Best regards,
- Roy Tucker
=================
(5) CHICXULUB IMPACT & THE DECCAN TRAPS
From Oliver Morton <abq72@pop.dial.pipex.com>
Benny
There was recently some more discussion on CCNet of the Deccan
traps as
an antipodal response to the Chicxulub impact, an idea I've
always
found rather intriguing. At the recent Geological Society of
America
meeting I had a chance to talk to David Kring of the University
of
Arizona, part of the group that put together the Chicxulub story.
He
told me that current geochronology clearly shows the Deccan event
predating the impact by, IIRC, two million years or so. Assuming
this
is correct, I suppose the impact might have had some effect on
the rate
of the flood volcanism, but it could hardly have been causal.
On another point, Olaf Stapledon had no call to predict world war
I
when he wrote "Last and First Men", since he had
already lived through
it, serving with distinction in the Friends' Ambulance Unit.
Best, oliver
============
(6) K-T BOUNDARY IMPACT-VOLCANIC CONNECTION?
From Andrew Glikson <andrew.glikson@anu.edu.au>
Dear Benny,
In response to Oliver Morton's letter, the suggestion of
antipodal
Chicxulub-Deccan connection (Rampino and Caldeira, 1992,
Geophys. Res.
Lett. 19, p. 2011) appears to be inconsistent with the 120
degrees
radial distance between these features on plate tectonic
reconstructions
(see Fig. 4 in Sutherland, 1996, AGSO Journal 16: p.572). This in
itself does not disprove a possible non-antipodal relation,
depending on
models of seismic shock propagation (Boslough et al., 1996, GSA
Special
Paper 307, p. 541). From Ar-Ar work by Basu et al. (1993, Science
261,
p. 902) and Venkatesan et al. (1993, EPSL 119, p. 181) the main
Deccan
trap volcanism has been preceded by minor rift-confined alkaline
volcanics c. 68.5 Ma and a basaltic phase about 66 Ma, and lasted
as
late as 63 Ma. While there is some dispute regarding the accuracy
of
the Ar-Ar ages (Feraud and Courtillout, 1994, EPSL 122, p.259),
it is
possible that (1) impact and volcanism were not genetically
connected;
(2) impact enhanced rather than triggered volcanism; (3) there
has been
more than one impact, by analogy to impact clusters in the late
Triassic, late Jurassic and late Eocene, and (4) the yet-unproven
"Shiva
crater" (Negy et al., 1992, Tectonophysics 206, p.341)
beneath the
Deccan basalts being a possible candidate? Since the
mega-impact record
is only partly known, and as new mega-craters are being
progressively
discovered, including in this part of the world, the jury is
still out
regarding genetic impact-volcanic relations.
Andrew Glikson
12.11.1999
Research School of Earth Science
Australian National University
Canberra ACT 0200 Australia
andrew.glikson@anu.edu.au
============
(7) ANOTHER SCI-FI FABLE
From Stephen Ashworth <sa@astronist.demon.co.uk>
Dear Benny Peiser,
I am sceptical about this old sci-fi fable in which carbon-based
creatures (us) create their own successor -- whether saviour or
nemesis
-- in the form of germanium-based computer technology (see item
3, by
Arthur C. Clarke, CCNet 8 Nov. 1999).
May I suggest two points for consideration: (1) that just as
computers
become more powerful, at the same time it becomes easier for us
to
interact with them (consider the trend: punched cards, keyboard,
mouse,
speech recognition, and now experiments in thought-directed
computing
under way), and (2) that digital germanium-based thought has
turned out
to be just as fallible as analog carbon-based thought, only in
different ways. These ideas point, not to the replacement of
humans
with computers, but rather to a continuation of the present trend
towards symbiosis.
Stephen Ashworth
Webmaster, Space Age Associates
Fellow of the British Interplanetary Society
11 November 1999
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