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
--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
--Leonard David,, 5 March 2001

    Andrew Yee <>


    Phil Bland <>

    Andrew Glikson <>
    Iain Gilmour <>

    Hermann Burchard <>
    Robert Clements <>

    Michael Paine <>










     Australian Broadcasting Coporation, 6 March 2001


From Andrew Yee <>

Office of Public Relations
University of Rochester
Rochester, New York

CONTACT: Jonathan Sherwood, (716) 273-4726

March 2, 2001


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

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


From, 5 March 2001


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

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

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
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,


From Phil Bland <>


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


From Andrew Glikson <>
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 3648 Ma to 3528 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



From Iain Gilmour <>

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.



From Hermann Burchard <>
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.

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


Hermann Burchard


From Robert Clements <>

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 <>


From Michael Paine <>

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
(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

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

"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



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.

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


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.

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,
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.


Jones TP, Lim B: Extraterrestrial impacts and wildfires

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.

Jones TP, Univ Wales Coll Cardiff, Sch Biosci, Cardiff CF1 3US, S Glam,
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.


Morgan JV, Warner MR, Collins GS, Melosh HJ, Christeson GL: Peak-ring
formation in large impact craters: geophysical constraints from Chicxulub

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.

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,
Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA.
Univ Texas, Inst Geophys, Austin, TX USA.


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.

Tsujita CJ, Univ Western Ontario, Dept Earth Sci, London, ON N6A 5B7,
Univ Western Ontario, Dept Earth Sci, London, ON N6A 5B7, Canada.

Copyright 2001 Institute for Scientific Information


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)).

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


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.

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.


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

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.

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


From the Australian Broadcasting Coporation, 6 March 2001


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

Emergency Management from today will issue media updates on the Mir

2000 Australian Broadcasting Corporation

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