PLEASE NOTE:
*
CCNet 36/2001, 6 March 2001
---------------------------
"Twenty-one years after the landmark papers by Alvarez et
al., Smit,
Ganapathy, and Hsu et al., most geoscientists now accept the
compelling
evidence for an impact at the K-T. A growing number regard this
impact as
a major cause of the K-T mass extinction, indeed much research is
being
done on the precise mechanisms. However, this is one boundary and
one mass
extinction. The evidence for an impact having caused a second
mass
extinction must be subjected to the same degree scrutiny and must
be
just as convincing."
--Iain Gilmour, Open University, 5 March 2001
"Assume the best case scenario; & NEAR survives
hibernation. What's
the chances of the Deep Space Network being available for a
mission
contact experiment at this time? or, alternatively: how large a
radiotelescope would be required to contact the reactivated probe
ex-DSN?"
--Robert Clements, 5 March 2001
"Ask anybody in California. The term "power to the
people" has taken
on new meaning. Electrical energy shortfalls throughout that
state
have led to disruptive rolling blackouts, emergency power
purchases and
highly charged public outcries. California's electrical woes may
well be
mirrored throughout an increasingly energy-hungry United States
in
future years. [...] Now consider that some 6 billion humans are
huddled
together on this third rock from the Sun. Energy demands around
the
globe are growing in a quest for prosperity and independence for
all.
One sky-high solution is a promising renewable energy technology
-- space
solar-power systems. These systems could feed electricity to
Earth
around-the-clock."
--Leonard David, Space.com, 5 March 2001
(1) ANCIENT EARTH HAD MAGNETIC FIELD 3X STRONGER THAN ONCE
THOUGHT
Andrew Yee <ayee@nova.astro.utoronto.ca>
(2) POWER TO THE PEOPLE - FROM SPACE
Space.com, 5 March 2001
(3) EXPECTED IMPACT CRATERS AROUND P/T TRANSITION
Phil Bland <P.A.Bland@open.ac.uk>
(4) ORIGIN OF THE P-T EXTINCTION: RESPONSE TO IAIN GILMOUR'S
COMMENTS
Andrew Glikson <geospec@webone.com.au>
(5) EVIDENCE FOR P/T IMPACT REMAINS UNCONVINCING
Iain Gilmour <I.Gilmour@open.ac.uk>
(6) CORE/MANTLE BOUNDARY
Hermann Burchard <burchar@mail.math.okstate.edu>
(7) WILL NEAR AWAKE FROM THE DEAD?
Robert Clements <Robert.Clements@dva.gov.au>
(8) MURPHY'S LAW APPLIES TO NEOs
Michael Paine <mpaine@tpgi.com.au>
* ABSTRACTS *
(9) PERIODIC MASS EXTINCTIONS?
(10) A JURASSIC/CRETACEOUS (J/K) BOUNDARY IMPACT?
(11) XTERRESTRIAL IMPACTS AND WILDFIRES
(12) PEAK-RING FORMATION IN LARGE IMPACT CRATERS
(13) MUTIPLE CAUSES OF CATASTROPHIC EVENTS
(14) IMPACT VAPORIZATION AND IONIZATION OF COSMIC DUST PARTICLES
(15) BACTERIAL SPORES SURVIVE SIMULATED IMPACT
(16) NEW FINDS OF AUSTRALIAN MICROTEKTITES
(17) OH DEAR: LACKING MIR INSURANCE WORRIES AUSSIES
Australian Broadcasting Coporation, 6
March 2001
=============
(1) ANCIENT EARTH HAD MAGNETIC FIELD 3X STRONGER THAN ONCE
THOUGHT
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Office of Public Relations
University of Rochester
Rochester, New York
CONTACT: Jonathan Sherwood, (716) 273-4726
March 2, 2001
ANCIENT EARTH HAD MAGNETIC FIELD 3X STRONGER THAN ONCE THOUGHT
A new technique for measuring the Earth's magnetic field back to
the days of
the dinosaurs and beyond has revealed that the magnetic field was
as much as
three times stronger in ancient Earth than previous techniques
suggested.
The new method could help scientists better understand ancient
Earth,
including how its molten core behaved in its early days. The
results of the
first field test of the new technique appear in the March 2 issue
of
Science.
Scientists use the record of the Earth's magnetic field locked in
rocks to
tease out secrets of the geodynamo -- the currents of molten rock
that
seethe beneath the Earth's crust, causing everything from
earthquakes and
volcanoes to the drift of the continents themselves. The Earth's
magnetic
field also protects us from much of the sun's dangerous
radiation, so
understanding how it works can help scientists predict its
fluctuations and
look into what effect those fluctuations could have had on the
development
of life on Earth.
Researchers have known that the magnetic poles have flipped
several times
during our planet's lifetime -- meaning a compass 100,000 years
ago could
have pointed south instead of north. The record of the field is
captured in
tiny pieces of magnetic particles in new lava. The particles
orient
themselves just like a compass, until the lava cools around them,
locking
them into place. Great bands of rock displaying north-south flips
are laid
across the ocean floors.
"We know a lot about the directions of the Earth's magnetic
field," says
John Tarduno, professor of geophysics and chair of the Department
Earth and
Environmental Sciences at the University of Rochester and first
author of
the Science paper. "It's how we unravel plate tectonics and
learn something
about the core. But to understand the way the field works, you
also need to
know the field's magnitude, and we don't know nearly enough about
that."
The traditional approach to measuring the ancient Earth's
magnetic field
strength (called paleointensity) was developed more than four
decades ago,
and has changed little until Tarduno's technique. In the old
method, a piece
of igneous rock about an inch across is heated and cooled in a
chamber that
is shielded from any magnetic sources. The magnetism is
essentially
"drained" from the magnetic particles in the rock, like
siphoning water out
of a jug. The researchers then "refill the jug,"
measuring how much
magnetism the particles can hold. Two significant drawbacks
result from this
method, however: a piece of rock hundreds of millions of years
old often
becomes contaminated over time, and the process often imparts a
magnetism to
the rock -- like water leaking into the jug before you refill it.
As a
consequence, very ancient samples seem to hold little
magnetization, further
confounding results that were already in question because of
contamination.
Tarduno decided to see if he could use the University's
Superconducting
Quantum Interference Device (nicknamed "SQUID"), a
device normally used in
computing chip design, which is extremely sensitive to the
tiniest magnetic
fields. "With the SQUID we realized that we could start
measuring single
crystals instead of whole rocks," says Tarduno. "That
let us use samples we
knew had no contamination."
Early tests showed that feldspar, the most common mineral on the
Earth's
surface, worked well since it created a microscopic shell around
slivers of
magnetite, protecting them from contamination. Tarduno's team
took samples
from a 1955 lava flow in Hawaii and tried to determine if the
paleointensity
reading would match the actual Earth's magnetic field strength in
1955. It
did. Tarduno was essentially doing the same heating/cooling test
that had
been done for 40 years on large samples, yet doing it on samples
the size of
a grain of sand, without the possibility of contamination and
with much more
accurate results.
"We can now measure paleointensity in places we could never
measure anything
before," says Tarduno. "And the results are more
reliable than ever before."
With the method tested, it was time for Tarduno to see what it
revealed
about the magnetic field back in the days of the dinos. His team
took dozens
of samples from lava flows in India that were nearly 100 million
years old
-- an unusual time in Earth's history when the field was not
reversing --
and found that the intensity of the field was three times
stronger than the
old method suggested. Besides possibly giving T-Rex a better
northern lights
show, the field strength gives researchers a glimpse into what
the Earth's
hot, molten core was doing back then.
"Our findings suggest that there is a relationship between
magnetic
reversals and paleointensity," says Tarduno. "Such a
relationship fits very
well with supercomputer models. It's an exciting time. We're
really starting
to understand how the heart of our planet works."
Tarduno will use the new method to plot the paleointensity of
different eras
in ancient Earth's past. Some of his more challenging work is in
the
paleointensity of rocks 2.5 billion years old -- more than
halfway back to
Earth's very beginning. The task is especially challenging
because
scientists believe that the core of the Earth that controls the
magnetic
field was still forming.
Post doctoral student Rory Cottrell and graduate student Alexei
Smirnov,
both from the University of Rochester, are also authors on the
Science
paper.
=============
(2) POWER TO THE PEOPLE - FROM SPACE
From Space.com, 5 March 2001
http://www.space.com/businesstechnology/technology/space_solarpower_010302.html
POWER PLUGS IN SPACE
By Leonard David
Senior Space Writer
WASHINGTON -- Ask anybody in California. The term "power to
the people" has
taken on new meaning. Electrical energy shortfalls throughout
that state
have led to disruptive rolling blackouts, emergency power
purchases and
highly charged public outcries.
California's electrical woes may well be mirrored throughout an
increasingly
energy-hungry United States in future years.
That bleak prospect earned a few minutes of speech time by newly
elected
President George W. Bush last Tuesday. "We have a serious
energy problem
that demands a national energy policy," President Bush said
in his first
speech to Congress.
"Our energy demand outstrips our supply. We can produce more
energy at home
while protecting our environment, and we must. We can produce
more
electricity to meet demand, and we must. We can promote
alternative energy
sources and conservation, and we must. America must become more
energy
independent, and we will," Bush said.
Sky-high solution
Now consider that some 6 billion humans are huddled together on
this third
rock from the Sun. Energy demands around the globe are growing in
a quest
for prosperity and independence for all.
One sky-high solution is a promising renewable energy technology
-- space
solar-power systems. These systems could feed electricity to
Earth
around-the-clock.
Growing constantly, a spirally constructed solar power satellite,
or Solar
Disk, will have a final diameter of more than 5 km. Photovoltaic
blanket
rolls transported to orbit are then deployed around the perimeter
of the
disk. Once the blankets are attached to the slowly spinning disk,
integrated
flat power cables are liked by radial power buses attached by a
construction
"spider" that travels along the rotating construction
beam.
Power-beaming satellites are not new. The idea has energized
considerable
study, discussion and debate for nearly 35 years.
What's new is the fast-paced march of technology. Furthermore,
numbers of
countries, including Japan, France, Germany and Canada are
carrying out
studies as well as experiments to scope out the promise of
transmitting
solar energy via laser or microwave link from space to power
grids on Earth.
"Space solar power is something that should be explored
seriously, not
written off as science fiction," said Bryan Erb, president
of the Sunsat
Energy Council in Houston, Texas. Advances in materials,
higher-efficiency
solar cells, space robotics to build the large structures -- all
these and
other developments contribute to making a cost-effective space
power system,
he told SPACE.com.
Experts also point out that solar energy gathered in Earth orbit
can be
conveyed via wireless transmission not only to terra firma, but
to spots in
space as well.
Fresh look
NASA has taken a fresh look at the viability of large-scale space
solar-power systems, doing so over the last few years, said John
Mankins,
NASA manager for the Human Exploration and Development of Space
Technology
and Commercialization Initiative.
"Reasonable progress is being made. Technical hurdles have
been better
explored. Nevertheless, major technical, regulatory and
conceptual hurdles
continue to exist," Mankins said.
NASA has crafted a strategic road map for space solar power
(SSP).
Mankins said that by 2006-2007, demonstrations of wireless power
transmission could be carried out at the International Space
Station. A
100-kilowatt power class SSP platform might also test out
point-to-point
wireless power transmission in this time period.
By the 2011-2012 time frame, a 1-megawatt class SSP platform
could validate
space-to-space and space-to-surface wireless power transmission,
Mankins
said.
A SunTower comprising many sets of lightweight, inflatable
fresnel
reflectors, focuses the sun's energy on small arrays of highly
efficiency
photovoltaic cells. The energy is then converted to radio
frequencies and
beamed to receivers on Earth to support the ever-increasing needs
of the
growing world population. The satellite components are carried
into orbit by
a highly reusable launch vehicle using both air-breathing and
rocket engines
for propulsion.
Within the next 15-20 years, an SSP platform cranking out
10-megawatts of
energy might be workable. By 2025-2035, a full-scale SSP platform
looks
feasible and capable of producing 1-2 gigawatts of power.
Ultimately,
Mankins said, in the post-2050 time frame, a 10-gigawatt power
class SSP
platform could become viable.
An incremental, stepping up of power levels would shake out SSP
technologies
and power management ideas. Terrestrial power beaming and a range
of space
science, exploration and commercial activities in Earth orbit --
such as
space business parks or energizing large communications platforms
-- could
be supported by taking this approach, Mankins said.
Near-term market
Is there a market for in-space delivery of power?
"You bet," said Molly Macauley, research fellow at
Resources for the Future,
a think tank on energy and environmental issues. Communications
satellites
and remote-sensing spacecraft would benefit by being recharged
from
time-to-time by a power-beaming satellite, she said.
"It would be great even if the International Space Station
didn't have to
have those big, cumbersome football field sized arrays,"
Macauley said. "An
SSP could be like in-flight refueling -- constantly," she
said.
"Right now, there's a near-term market for this. The
question is how do we
configure the SSP system to best serve that market? That's the
next step,"
Macauley said.
View from Congress
Orbiting power stations as an environmentally friendly,
economical energy
technology for Earth is strongly backed by Margo Deckard,
director and space
solar-power project manager for the Space Frontier Foundation,
based in
Studio City, California.
At a Feb. 28 "Space Roundtable" on Capitol Hill here,
Deckard joined other
SSP supporters to discuss space solar power as an investment in
our energy
future. She emphasized that a natural development plan for SSP is
needed.
Deckard and the Space Frontier Foundation called for a government
role in
the early stages of SSP technology development, with private
industry
commercializing the technology in the later stages.
To kick the effort off, Deckard proposed that NASA establish a
space
solar-power program akin to the space agency's Discovery-class
armada of
cheaper, better, faster spacecraft. "Specifically, we are
calling for a
five-year program, at a total cost of $295 million, to enable a
space-to-Earth power transmission demonstration.
"We also believe that not only will SSP deliver a benefit to
consumers on
Earth, but will also contribute to opening the space frontier to
human
settlement by providing power in space," she said.
It seems that power-beaming satellites may have already found a
friend in
Congressman Dana Rohrabacher (R-California), chairman of the
Space and
Aeronautics Subcommittee in the House of Representatives.
"I think we need to take positive steps toward space
solar-power systems,"
the lawmaker told the round table, promising to push for new SSP
research
monies over the next few years. "We need to move in a
step-by-step manner,"
Rohrabacher said.
"It's a real possibility to have a great new energy source
for mankind,"
Rohrabacher said.
Copyright 2001, Space.com
============================
* LETTERS TO THE MODERATOR *
============================
(3) EXPECTED IMPACT CRATERS AROUND P/T TRANSITION
From Phil Bland <P.A.Bland@open.ac.uk>
Benny,
Just a quick word on the PT boundary and this possibly associated
crater.
Most estimates of the rate of production of craters >40km on
the Earth
suggest that we should see at least one crater of this size, and
possibly
more, within the 6-10 million years that seems to be the error on
the age
estimates for the Araguinha structure ie. unless we get better
constraints
on this age, it's not at all surprising that there is a crater of
this size
within 3-5 Ma of the PT.
Phil Bland
===================
(4) ORIGIN OF THE P-T EXTINCTION: RESPONSE TO IAIN GILMOUR'S
COMMENTS
From Andrew Glikson <geospec@webone.com.au>
Dear Benny,
In his comment "more problems with P/T "impact"
evidence" (CCNet 05-03-01),
responding to my communication ("Evidence for P/T boundary
impact/s from the
age of a large Brazilian impact crater and from shocked quartz in
P-T
boundary sediments", CCNet 05-03-01), I. Gilmour writes:
"if a crater this
size (Araguinha - 42 km) could cause an extinction the size of
the P-T then
we really should be worried!". This misrepresents my
letter, where it is
stated: "The real question is whether the magnitude of the
impact/s has been
sufficient to trigger the Norilsk volcanism and the P-T boundary
mass
extinction? Clearly, the size of Araguinha (42 km) is
insufficient in this
regard." (CCNet 05-03-01).
Gilmour seeks to question the occurrence of impacts along the P-T
boundary
on the basis of: (1) doubts about the coincidence or otherwise of
Araguinha
(245.5 +/- 3.5 Ma and 243.3 +/- 3.0 Ma - Ar-Ar ages on impact
melt) with the
P-T boundary (251.4 Ma+/-0.3); (2) doubts regarding the
precise
stratigraphic location of the P-T boundary suggested by Retallack
et al.
(1998) in connection with the discovery of shocked quartz grains
at Mount
Crean, southern Victoria Land, Antacrtica; (3) the low abundance
and small
size (176 microns) of shocked quartz fractions; (4) the low
Ir anomalies
along the P-T boundary. While a genetic connection between
impacts,
volcanism and mass extinction along the P-T boundary remains
hypothetical,
nor do the points made by Gilmour constrain this possibility, for
the
following reasons:
1. In so far as the Ar-Ar ages of Araguinha impact may be
2-3 million years
younger than the P-T boundary -
A. asteroid/comet impacts may occur as clusters over intervals of
several
million years, as attested by the late Devonian (Woodleigh, Alamo
Breccia,
Siljan, Charlevoix, Kaluga), late Triassic (Manicouagan,
Putchez-Katunski,
Saint Martin) and late Jurassic (Morokweng, Mjolnir, Gosses
Bluff) clusters.
Mass extinctions may in some instances represent the cumulative
effects of
several impacts and related environmental consequences.
B. post-impact long term hydrothermal activity within crater
aureoles can
result in isotopic age resetting of primary impact ages.
For example, at
the 120 km-diameter Woodleigh impact structure, Western
Australia, K-Ar ages
of illite and smectite range from 364±8 Ma to 352±8 Ma to 342
Ma (Mory et
al., 2001, EPSL, 184, 359-365).
2. In so far as the P-T extinction was caused by the cumulative
effect of an
impact cluster, the precise stratigraphic positions of shocked
quartz and Ir
anomalies may vary over the age interval of such a cluster.
Referring to
Gilmour's points (3) and (4) above, the amount and grain size of
shocked
quartz are related to the composition of the target rocks and the
distance
of the source crater/s, respectively. For example, impacts
on oceanic
basaltic crust will produce little or no shocked quartz.
Nor will cometary
impacts result in strong Iridium anomalies.
Referring to Gilmour's call for "the need for detailed,
rigorous research."
- I suggest Rettalack et al.'s work is an example of such
excellent
research. While no serious scientist is claiming a demonstrable
genetic link
between impacts, Norilsk volcanism and P-T extinction, nor can
this
possibility be refuted at the present state of knowledge. In
particular, the
role of cometary oceanic impacts, which may be difficult to test
due to
subduction, low abundances of shocked quartz and weak Ir
anomalies, remains
a tantalizing possibility.
Andrew Glikson
Australian National University
Canberra, ACT 0200
06-03-01
===========
(5) EVIDENCE FOR P/T IMPACT REMAINS UNCONVINCING
From Iain Gilmour <I.Gilmour@open.ac.uk>
Dear Benny:
I have no real problems with Glikson's response. Afterall, I
don't dispute
the possibility that the P-T extinction may be impact related,
but to my
mind the evidence remains unconvincing.
I certainly don't query the carefulness of Retallack et al's
study, but
CCNET readers should be aware that questions were raised in the
peer-reviewed literature at the time as to whether there was
sufficient
biostratigraphic information available to constrain the P-T
transition in
the sections studied. Not a mute point, if the actual P-T
transition can't
be located precisely enough then correlation to other successions
will be
well nigh impossible. These sorts of questions will not surprise
the
geologists amongst CCNET's readership; geology is an
observational and
interpretive science.
Glikson draws attention to one of several factors that can cause
errors in
age determinations thereby making it more difficult to
demonstrate any
coincidence without the supporting evidence of stratigraphic
correlation. As
I previously mentioned, it is this demonstrable coincidence at
the K-T that
makes such a compelling argument for a link between an impact
event and a
mass extinction.
On a philosophical note. Twenty-one years after the landmark
papers by
Alvarez et al., Smit, Ganapathy, and Hsu et al., most
geoscientists now
accept the compelling evidence for an impact at the K-T. A
growing number
regard this impact as a major cause of the K-T mass extinction,
indeed much
research is being done on the precise mechanisms. However, this
is one
boundary and one mass extinction. The evidence for an impact
having caused a
second mass extinction must be subjected to the same degree
scrutiny and
must be just as convincing.
Iain
=============
(6) CORE/MANTLE BOUNDARY
From Hermann Burchard <burchar@mail.math.okstate.edu>
Dear Benny,
thanks for posting my notes on CCNet. Deep mantle convection and
plumes
rising from the core-mantle boundary are apparently real, after
all. Deep
Earth structure has become quite well known using seismic
tomography and
mineral physics, as I am beginning to learn. Here is one
excellent
article that I could find by Michael Wysession of Washington
University, St.
Louis, MO. This particular work is five or six years old, so even
better
results may exist now that I have not been able to locate yet.
http://www.sigmaxi.org/amsci/articles/95articles/Wysession-full.html
After I sent my last note to you, it bothered me that I had
written "..the
mantle is not being heated from below..". I realized I had
not checked this
out. Would there be more Uranium and Thorium in the core of Earth
than in
the mantle? The above article doesn't address this question
directly (see below; radioactive potassium 40 is mentioned as a
possibility
in connection with the core), and the answer may not be known.
Also, there
is no mention made at all of cosmic impacts, hence neither of any
connections of mantle plumes and impacts. The mechanism suggested
for plume generation does seem to be based on a few hypotheses
that are not
so certain, and I continue to favor an impact-genetic
explanation. After
reading the above work, it looks possible, that lower pressure
due to
crustal excavation in an impact explosion might start a plume
going all the
way down to the core-mantle boundary.
Surprisingly, outer core temperature and density have lower and
less certain
values than used to be given in the past, with few data for the
inner core
stated at all, if any. Actinides -- Uranium, Thorium, and
Potassium 40 --
dispersed evenly in the mantle are seen as primary heat sources.
Core heat
output does not seem all that certain or important any longer.
Quoting: "In
addition to the primordial heat that is still flowing from the
core into the
mantle, mantle convection has a heat source that is generated
internally by
the radioactive decay of unstable isotopes such as uranium-235,
uranium-238,
thorium-232 and potassium-40." The older, very natural
notion is of
actinides heating the core. That view now seems ruled out,
apparently by
constraints on core density. Core temperature may exceed the
bottom of the
mantle only by 500 degree C.
Convection in the upper mantle is predominant to a depth of 660
km. Again,
quoting: "..upper and lower .. mantle .. behave largely
independently." In
the lower mantle very high viscosity (30 to a 100 times greater
than upper
mantle) slows down convection to move on a much longer time
scale. Seismic
velocities vary by a few percentage points only. Near steady
state
conditions appear agreed upon generally in the lower mantle when
measured as
against the upper mantle with its much more rapid time scales of
convection
(at a few centimeters a year). Time scale for events at the
bottom of the
mantle is given in billions of years.
But notice strange "anticontinents" making their
appearance at the
core-mantle boundary, mirroring the lands on the crust of the
planet. This
seems to require dynamic coupling, perhaps via plumes, at a much
faster
rate. Direct seismic evidence for plume activity in the lower
mantle is
tenuous given the small variations in signal speed.
Two arguments are made for convection in the lower mantle. First,
the great
plumes (Hawaii, Yellowstone, Galapagos, the African hotspots,
etc, are
mentioned by name) apparently are anchored firmly in the lower
mantle as
they do not participate in plate tectonics. Second, high seismic
velocities
are seen near subduction zones of greatest age. Younger zones
have the
subducted slab lie down flat on the 660 km discontinuity. At the
older
zones, in order to explain higher velocities of earthquake
signals in these
areas by the lower temperature of the subducted slab, it is
surmised that
the slab is drawn beneath 660 km.
Here, it would seem possible to me instead that the ancient slab
in contact
with the lower mantle at the 660 km discontinuity has chilled the
underlying
denser rock over time (>100 Ma), although thermal conductivity
is said to be
very low, to sufficient extent that seismic velocities are raised
to
observed levels.
The fact that plumes convect all the way down to the core is
perhaps not all
that surprising, given that surface crust is excavated initially
by impact
explosion. Once the pressure is lowered in the zone under the
plume by
basalt flooding to the surface, and expecting some anisotropy in
the nearly
rigid and highly viscous lower mantle, there may not be any
stopping for a
chain of phase transitions to propagate all the way down to the
core.
Wysession's article provides excellent factual detail regarding
the mineral
physics and the phase transitions which ultimately are
responsible for the
existence of the various discontinuous layers. This picture
based on the
best geophysics data from the deep mantle available five years
ago, in
overall terms may not be all that different from the one that I
tried to
paint, with much cruder brush strokes, except for a complete
neglect of any
impact scenarios in Wysession's account.
Of the rest of my March 1 note to CCNet, I hope that some of my
guesses on
the geology of Sibiria (where placer deposits of gold and
diamonds in Far
Eastern Sibiria are significant indicators of a relationship with
a still
controversial impact scenario at Norilsk), the Yucatan, etc, can
be
sustained.
Regards,
Hermann Burchard
============
(7) WILL NEAR AWAKE FROM THE DEAD?
From Robert Clements <Robert.Clements@dva.gov.au>
Please forgive this late comment; but i've be in the mountains of
western
Guangdong watching preparations for the rice planting. It's a
long story....
Assume the best case scenario; & NEAR survives hibernation.
What's the
chances of the Deep Space Network being available for a mission
contact
experiment at this time?; or, alternatively: how large a
radiotelescope
would be required to contact the reactivated probe ex-DSN? I know
that a
number of independent mission designers are looking at the old
Soviet spysat
telescopes in the Baltics & elsewhere as potential cutprice
command &
control systems for nearEarth missions.
All the best,
Robert Clements <Robert.Clements@dva.gov.au>
============
(8) MURPHY'S LAW APPLIES TO NEOs
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
Although it seems a slight diversion from regular CCNet topics,
the item
about a "Murphy's Law" experiment is interesting. The
April (no joke) 97
edition of Scientific American had a good article The Science of
Murphy's
Law http://www.sciam.com/0497issue/0497quicksummary.html
(not available online)
It explains the physics of toast falling butter side down (to do
with the
height of the table which is related to the height of a human
which is
related to the strength of gravity which determines the forces
acting on the
toast... sorry to ruin it for those school kids doing the
experiment!)
The "deceleration" experiment that led to Murphy's Law
was actually a sled
test by Dr John Stapp, who became famous in road safety circles.
Not wishing
to endanger "volunteers" he strapped himself into the
sled and unwent
decelerations that, literally, made his eyes (almost) pop out.
After one
particularly severe run he asked Murphy for the readings and was
told the
instrumentation had been set up incorrectly so it was all in
vain.
More importantly, the son of Murphy also wrote in with MURPHY WAS
A
PERFECTIONIST
http://www.sciam.com/0897issue/0897letters.html
"I would suggest, however, that Murphy's Law actually refers
to the
CERTAINTY of failure. It is a call for determining the likely
causes of
failure in advance and acting to prevent a problem before it
occurs."
Here here!
Michael Paine
=============
* ABSTRACTS *
=============
(9) PERIODIC MASS EXTINCTIONS?
Prokoph A, Fowler AD, Patterson RT: Periodically forced
self-organization in
the long-term evolution of planktic foraminifera CANADIAN JOURNAL
OF EARTH
SCIENCES 38: (2) 293-308 FEB 2001
Wavelet transform and other signal analysis techniques suggest
that the
planktic foraminiferal (PF) long-term evolutionary record of the
last 127 Ma
can be attributed to complex periodic and nonlinear patterns.
Correlation of
the PF extinction pattern with other geological series favors an
origin of
the similar to 30 Ma periodicity and self-organization by
quasi-periodic
mantle-plume cycles that in turn drive episodic volcanism,
CO2-degassing,
oceanic anoxic conditions, and sea-level fluctuations. Stationary
similar to
30 Ma periodicity and a weak secular trend of similar to 100 Ma
period are
evident in the PF record, even without consideration of the mass
extinction
at the K-T boundary. The 27-32 Ma periodicity in the impact
crater record
and lows in the global sea-level curve, respectively, are similar
to 6.5 Ma
and similar to 2.3 Ma out of phase with PF-extinction data,
although major
PF-extinction events correspond to the bolide impacts at the K-T
boundary
and in late Eocene. Another six extinction events correspond to
abrupt
global sea-level falls between the late Albian and early
Oligocene.
Self-organization in the PF record is characterized by increased
radiation
rates after major extinction events and a steady number of
baseline species.
Our computer model of long-term PF evolution replicates this SO
pattern. The
model consists of output from the logistic map, which is forced
at 30 Ma and
100 Ma frequencies. The model has significant correlations with
the relative
PF-extinction data. In particular, it replicates singularities,
such as the
K-T event, nonstationary 2.5-10 Ma periodicities, and phase
shifts in the
similar to 30 Ma periodicity of the PF record.
Addresses:
Fowler AD, Univ Ottawa, Ottawa Carleton Geosci Ctr, POB 450,
Ottawa, ON K1N
6N5, Canada.
Univ Ottawa, Ottawa Carleton Geosci Ctr, Ottawa, ON K1N 6N5,
Canada.
Univ Ottawa, Dept Earth Sci, Ottawa, ON K1N 6N5, Canada.
Carleton Univ, Ottawa Carleton Geosci Ctr, Ottawa, ON K1S 5B6,
Canada.
Carleton Univ, Dept Earth Sci, Ottawa, ON K1S 5B6, Canada.
Copyright © 2001 Institute for Scientific Information
==============
(10) A JURASSIC/CRETACEOUS (J/K) BOUNDARY IMPACT?
McDonald I, Andreoli MAG, Hart RJ, Tredoux M: Platinum-group
elements in the
Morokweng impact structure, South Africa: Evidence for the impact
of a large
ordinary chondrite projectile at the Jurassic-Cretaceous boundary
GEOCHIMICA
ET COSMOCHIMICA ACTA 65: (2) 299-309 JAN 2001
Radiometric dating of melt rocks at impact craters has revealed
that some
giant impacts appear to overlap in time with major boundaries in
Earth
history [e.g., the Cretaceous-Tertiary (K/T) and
Jurassic-Cretaceous (J/K)
boundaries]. The Morokweng impact crater in South Africa is
coincident in
age with the J/K boundary. However, the types of objects that
generate large
craters are poorly known because it is difficult to unambiguously
identify
the projectile from the signature it imparts into the impact
rocks.
Meteorites are highly enriched in the platinum-group elements
(PGE), which
have been widely used as a tool for identifying the presence of a
meteorite
signature. Here we present new PGE analyses from the Morokweng
impact melt
sheet. Our data reveal high PGE concentrations and high degree of
PGE
correlation through the melt sheet. Regression analysis was used
to
determine the projectile PGE signature and constrain input from
the
terrestrial target rocks. The closest match to Morokweng is the
PGE
signature of ordinary (L or LL) chondrite meteorites, which is
broadly in
agreement with the results of an earlier Cr isotope study. The
results of
these independent studies provide strong evidence that a large,
ordinary
chondrite projectile struck the area of Morokweng in the late
Jurassic.
Copyright (C) 2001 Elsevier Science Ltd.
Addresses:
McDonald I, Univ Greenwich, Sch Earth & Environm Sci, Chatham
Maritime ME4
4TB, Kent, England.
Univ Greenwich, Sch Earth & Environm Sci, Chatham Maritime
ME4 4TB, Kent,
England.
Univ Witwatersrand, Schonland Res Ctr, ZA-2050 Wits, South
Africa.
NECSA, ZA-0001 Pretoria, South Africa.
Univ Cape Town, Dept Geol Sci, ZA-7700 Rondebosch, South Africa.
=============
(11) XTERRESTRIAL IMPACTS AND WILDFIRES
Jones TP, Lim B: Extraterrestrial impacts and wildfires
PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY 164: (1-4) 57-66
DEC 2000
Small extraterrestrial impacts are inefficient at starting fires,
and the
evidence connecting larger impacts with wildfires is not secure.
The
association between impacts and wildfires has been re-assessed by
reviewing
records of recent small impacts, examining material incorrectly
identified
as 'charcoal' from the Miocene Ries impact crater, and charcoal
from K-T
boundary sediments. Fossil charcoal was collected from five
well-researched
K-T sites, and examined using scanning electron microscopy and
reflected
light microscopy. An important discovery was that a significant
proportion
(53%) of the charcoal fragments examined, from all five sites,
displayed
features interpreted as resulting from biodegradation prior to
being
charcoalified. Furthermore, there was a complete absence of
morphological
features recognised as resulting from the charring of living
plants. The
clear inference from this observation is that there could have
been a
significant time lag (months, years, and possibly decades)
between plant
mortality and the firsts) that preserved them as charcoal, maybe
involving
accelerated drying-out due to impact-related atmospheric
processes. These
results do not support or oppose the extraterrestrial impact
hypothesis, but
do suggest that any putative impact(s) was not immediately
followed by
'global' wildfires. (C) 2000 Elsevier Science B.V. All rights
reserved.
Addresses:
Jones TP, Univ Wales Coll Cardiff, Sch Biosci, Cardiff CF1 3US, S
Glam,
Wales.
Univ Wales Coll Cardiff, Sch Biosci, Cardiff CF1 3US, S Glam,
Wales.
Environm Directorate OECD, Intergovt Panel Climate Change Unit
Greenhouse
Ga, F-75016 Paris, France.
=============
(12) PEAK-RING FORMATION IN LARGE IMPACT CRATERS
Morgan JV, Warner MR, Collins GS, Melosh HJ, Christeson GL:
Peak-ring
formation in large impact craters: geophysical constraints from
Chicxulub
EARTH AND PLANETARY SCIENCE LETTERS 183: (3-4) 347-354 DEC 15
2000
A seismic reflection and three-dimensional wide-angle tomographic
study of
the buried, similar to 200-km diameter, Chicxulub impact crater
in Mexico
reveals the kinematics of central structural uplift and peak-ring
formation
during large-crater collapse. The seismic data show downward and
inward
radial collapse of the transient cavity in the outer crater, and
upward and
outward collapse within the central structurally uplifted region.
Peak rings
are formed by the interference between these two flow regimes,
and involve
significant radial transport of material. Hydrocode modeling
replicates the
observed collapse features. Impact-generated melt rocks lie
mostly inside
the peak ring; the melt appears to be clast-rich and
undifferentiated, with
a maximum thickness of 3.5 km in the center. (C) 2000 Elsevier
Science B.V.
All rights reserved.
Addresses:
Morgan JV, Univ London Imperial Coll Sci Technol & Med, TH
Huxley Sch,
London SW7 2BP, England.
Univ London Imperial Coll Sci Technol & Med, TH Huxley Sch,
London SW7 2BP,
England.
Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA.
Univ Texas, Inst Geophys, Austin, TX USA.
=========
(13) MUTIPLE CAUSES OF CATASTROPHIC EVENTS
Tsujita CJ: The significance of multiple causes and coincidence
in the
geological record: from clam clusters to Cretaceous catastrophe
CANADIAN
JOURNAL OF EARTH SCIENCES 38: (2) 271-292 FEB 2001
Specific causes of unusual events recorded in the geological
record are
commonly difficult to distinguish and isolate; in some instances,
event
strata contain features that cannot be explained by a single
causal
mechanism. Unicausal hypotheses, when applied to complex
problems, can lead
to the misidentification, misinterpretation, and force-fitting of
observations ("great expectations syndrome"). The close
timing or temporal
overlap of significant events, although statistically improbable
on short
time scales, becomes possible on long time scales. Event
coincidence may
occur on a wide range of scales, from local to global. On the
local scale, a
multiple-event interpretation is offered for both the
concentration and
clustering of bivalves at specific levels within the Upper
Cretaceous
Bearpaw Formation of southern Alberta. For this example, the
relative timing
of fluctuations in benthic substrate texture, oxygen
concentration,
abundance of planktotrophic larvae, and degree of sea-floor
scouring was
crucial to the formation and preservation of shell
concentrations. On the
sharply contrasted global scale, the implications of multiple
events warrant
much closer consideration than they have received hitherto in
terms of major
proposed causes for the Cretaceous-Tertiary (K-T) mass-extinction
event:
bolide impact, sea-level change, climatic change, and
flood-basalt
volcanism. By considering the predictable effects of these
synchronous
factors, both individually and in combination, a multiple-cause
explanation
of the K-T mass extinction emerges as entirely plausible.
Certainly it needs
to be considered in all future investigations of this important
issue.
Addresses:
Tsujita CJ, Univ Western Ontario, Dept Earth Sci, London, ON N6A
5B7,
Canada.
Univ Western Ontario, Dept Earth Sci, London, ON N6A 5B7, Canada.
Copyright © 2001 Institute for Scientific Information
========
(14) IMPACT VAPORIZATION AND IONIZATION OF COSMIC DUST PARTICLES
Hornung K, Malama YG, Kestenboim KS: Impact vaporization and
ionization of
cosmic dust particles
ASTROPHYSICS AND SPACE SCIENCE 274: (1-2) 355-363 2000
We report on theoretical efforts to understand the process of
vaporization
and ion formation upon hypervelocity impact of small cosmic dust
particles
on a solid surface. Such collisions occur at the surface of solid
bodies
within the planetary system, which do not have an atmosphere as
well as in
various actual and upcoming space missions for in-situ
measurements of
interplanetary, interstellar and cometary dust. The investigation
uses
Godunov's method to simulate the impact. For the very high
velocitites
investigated, the impacting dust particle as well as parts of the
target
vaporize and some of the vapor cloud may change to partially
ionized.
Numerical results of the impact process are communicated for an
80 km s(-1)
impact of a slightly porous SiO2 particle on a compact SiO2
surface. Values
of the amount of vapor and liquid excavated from the target are
given.
Ionization rates are calculated for the example investigated and
an estimate
is given how this extrapolates to the highest conceivable
velocities in the
planetary system (above 100 km s(-1)).
Addresses:
Hornung K, Univ BW Muenchen, Munich, Germany.
Univ BW Muenchen, Munich, Germany.
RAS, Inst Problems Mech, Moscow 117901, Russia.
Copyright © 2001 Institute for Scientific Information
=================
(15) BACTERIAL SPORES SURVIVE SIMULATED IMPACT
Horneck G, Stoffler D, Eschweiler U, Hornemann U: Bacterial
spores survive
simulated meteorite impact ICARUS 149: (1) 285-290 JAN 2001
A hypothetical interplanetary transfer of viable microorganisms
requires
that the microbes survive the following steps: (i) escape
process, (ii)
transient journey in space, and (iii) entry process. Step 1
involves
hypervelocity impact under strong shock metamorphism of the
ejected
microbe-bearing rock fragment. This paper reports experimental
studies on
the survival of microbes after a simulated meteorite impact. In
shock
recovery experiments with an explosive setup, spores of Bacillus
subtilis HA
101, immobilized between two quartz plates, were subjected to a
peak shock
pressure of 32 GPa, Although the spore layer showed an intense
darkening
after the shock treatment, up to 500 spores per sample survived,
resulting
in a survival rate up to 10(-4). This experimental pressure is in
the
pressure range which some martian meteorites have experienced
according to
well-calibrated shock effects of their mineral constituents. The
data
support the hypothesis that bacterial spores may survive an
impact-induced
escape process in a scenario of interplanetary transfer of life,
(C) 2000
Academic Press.
Addresses:
Horneck G, German Aerosp Ctr, DLR, Inst Aerosp Med, Cologne,
Germany.
German Aerosp Ctr, DLR, Inst Aerosp Med, Cologne, Germany.
Humboldt Univ, Museum Naturkunde, Inst Mineral, Berlin, Germany.
Ernst Mach Inst Kurzzeitdynam, Freiburg, Germany.
============
(16) NEW FINDS OF AUSTRALIAN MICROTEKTITES
Lee MY, Wei KY: Australasian microtektites in the South China Sea
and the
West Philippine Sea: Implications for age, size, and location of
the impact
crater
METEORITICS & PLANETARY SCIENCE 35: (6) 1151-1155 NOV
2000
Microtektites from two deep-sea cores in the South China Sea and
the West
Philippine Sea are identified as belonging to the Australasian
tektite
strewn field based on the morphology, chronostratigraphic
occurrence, and
geographical location of these microtektites. The higher
concentrations of
microtektites (>1000/cm(2)) in the marginal seas of the
western Pacific,
with the peak concentration in the South China Sea, support the
hypothesis
of a large impact crater in Indochina. These two new occurrences
lead to a
more precise dating of the impact event at 793 ka, whereas the
size of the
Australasian source crater on the Indochina Peninsula is
estimated to be
90-116 km.
Addresses:
Wei KY, Natl Taiwan Univ, Dept Geosci, 245 Choushan Rd, Taipei,
Taiwan.
Natl Taiwan Univ, Dept Geosci, Taipei, Taiwan.
Copyright © 2001 Institute for Scientific Information
===========
(17) OH DEAR: LACKING MIR INSURANCE WORRIES AUSSIES
From the Australian Broadcasting Coporation, 6 March 2001
http://www.abc.net.au/news/science/space/2001/03/item20010306080821_1.htm
RUSSIA ADMITS NO INSURANCE FOR MIR DAMAGE
Russia's space agency has admitted it does not have insurance
cover for any
damage caused by debris from the Mir Space Station when it is
brought down
from orbit this month.
A policy with a private company was to have been completed last
weekend, but
was complicated by discussion of multi-million dollar sums
involved in a
potential payout for accidental damage.
Up to 10 per cent of the heavier elements of the station are
expected to
survive the burn-up in the earth's atmosphere.
Russian space technicians say there is a 98 per cent chance the
debris will
fall as planned in the southern Pacific Ocean.
Emergency management officials in Australia are also confident
the debris
will fall harmlessly into the ocean.
Emergency Management Australia's David Templeman says there is
little chance
of Mir debris hitting Australia. Mr Templeman says 90 per cent of
the space
station will burn up on re-entry.
Nevertheless, Emergency Management has prepared contingency plans
liaising
with governments around the country on strategies if debris does
strike
Australia.
Emergency Management from today will issue media updates on the
Mir
situation.
© 2000 Australian Broadcasting Corporation
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