PLEASE NOTE:
*
CCNet 66/2002 - 7 June 2002
-----------------------------------
"Military strategists and space
scientists that wonder and worry about a
run-in between Earth and a comet or asteroid have additional
worries in
these trying times. With world tensions being the way they are,
even a small
incoming space rock, detonating over any number of political
hot-spots,
could trigger a country's nuclear response convinced it was
attacked by an
enemy. Being struck by a giant asteroid or comet isn't the main
concern for
Air Force Brigadier General Simon Worden, deputy director of
operations for
the United States Space Command at Peterson Air Force Base,
Colorado. "We
now have 8 or 10 countries around the world with nuclear
weapons...and not
all of them have very good early warning systems. If one of these
things
hits, say anywhere in India or Pakistan today, we
would have a very bad
situation. It would be awfully hard to explain to them that it
wasn't the
other guy," Worden pointed out."
--Leonard David, Space.com, 6 June 2002
"I think Mother Nature has given us yet
another wake-up call. Objects
the size of 2002 EM7 pass as close as this one did every two
weeks or so. We
just haven't found them all yet."
--Don Yeomans, JPL, 3 June 2002
(1) FIRST STRIKE OR ASTEROID IMPACT?
Space.com, 6 June 2002
(2) SCIENTISTS STUDY DEFENDING EARTH AGAINST ASTEROIDS
Scripps Howard News Service, 3 June 2002
(3) STUDY: "PERMIAN-TRIASSIC MASS EXTINCTION NOT CAUSED BY
COSMIC IMPACT"
CNN, 6 June 2002
(4) FORGET NEO IMPACTS: "VOLCANOES KILLED OFF PERMIAN
SPECIES"
Nature, 7 June 2002
(5) FLOOD BASALT: BIGGER AND BADDER
Science, 7 June 2002
(6) FORGET NEO IMPACTS: "COSMIC STORM KILLED OFF
DINOSAURS"
Andrew Yee <ayee@nova.astro.utoronto.ca>
(7) PERMIAN IMPACT CAUSED LARGEST MASS EXTINCTION ON EARTH
Space Daily, 31 August 2001
(8) AN EXTRATERRESTRIAL IMPACT AT THE PERMIAN-TRIASSIC BOUNDARY?
Science, Volume 293, Number 5539, Issue of 28
Sep 2001, p. 2343.
(9) ASTEROID TSUNAMI SIMULATION: NEW WAVE SUPERCOMPUTERS CATCH
BIG WAVES
Space Daily, 5 June 2002
(10) THE INSPIRATION OF ASTRONOMICAL PHENOMENA -- FOURTH
CONFERENCE
Rolf Sinclair <rolf@SANTAFE.EDU>
(11) CRATERS?
Giesinger Norbert <norbert.giesinger@siemens.com>
(12) WHY IS MARS SO HARD?
James Oberg <joberg@houston.rr.com>
================
(1) FIRST STRIKE OR ASTEROID IMPACT?
>From Space.com, 6 June 2002
http://space.com/scienceastronomy/astronomy/nss_asteroid_020606.html
First Strike or Asteroid Impact? The Urgent Need to Know the
Difference
By Leonard David
Senior Space Writer
DENVER, COLORADO -- Military strategists and space scientists
that wonder
and worry about a run-in between Earth and a comet or asteroid
have
additional worries in these trying times. With world tensions
being the way
they are, even a small incoming space rock, detonating over any
number of
political hot-spots, could trigger a country's nuclear response
convinced it
was attacked by an enemy.
Getting to know better the celestial neighborhood, chock full of
passer-by
asteroids and comets is more than a good idea. Not only can these
objects
become troublesome visitors, they are also resource-rich and
scientifically
bountiful worlds.
Slowly, an action plan is taking shape.
Noted asteroid and comet experts met here May 23-27, taking part
in the
National Space Society's International Space Development
Conference 2002.
Sweat the small stuff
Being struck by a giant asteroid or comet isn't the main concern
for Air
Force Brigadier General Simon Worden, deputy director of
operations for the
United States Space Command at Peterson Air Force Base, Colorado.
He sweats
the small stuff.
Worden painted a picture of the next steps needed in planetary
defense. His
views are not from U.S. Department of Defense policy but are his
own
personal perspectives, drawing upon a professional background of
astronomy.
For example, Worden said, several tens of thousands of years ago
an asteroid
just 165-feet (50 meters) in diameter punched a giant hole in the
ground
near Winslow, Arizona. Then there was the Tunguska event. In June
1908, a
massive fireball breached the sky, then exploded high above the
Tunguska
River valley in Siberia. Thought to be in the range of 165-feet
(50 meters)
to 330 feet (100 meters) in size, that object created a
devastating blast
equal to a 5 to 10 megaton nuclear explosion. A similar event is
thought to
have taken place in the late 1940s in Kazakhstan.
"There's probably several hundred thousand of these
100-meter or so
objects...the kind of ones that we worry about," Worden
said. However, these
are not the big cosmic bruisers linked with killing off dinosaurs
or
creating global catastrophes.
On the other hand, if you happen to be within a few tens of miles
from the
explosion produced by one of these smaller near-Earth objects,
"you might
think it's a pretty serious catastrophe," Worden said.
"The serious planetary defense efforts that we might mount
in the next few
decades will be directed at much smaller things," Worden
said. Some 80
percent of the smaller objects cross the Earth's orbit,
"some of which are
potentially threatening, or could be in the centuries
ahead," he said.
Nuclear trigger
One set of high-tech military satellites is on special
round-the-clock
vigil. They perform global lookout duty for missile launches.
However, they
also spot meteor fireballs blazing through Earth's atmosphere.
Roughly 30
fireballs detonate each year in the upper atmosphere, creating
equivalent to
a one-kiloton bomb burst, or larger, Worden said.
"These things hit every year and look like nuclear weapons.
And a couple
times a century they actually hit and cause a lot of
damage," Worden said.
"We now have 8 or 10 countries around the world with nuclear
weapons...and
not all of them have very good early warning systems. If one of
these things
hits, say anywhere in India or Pakistan today, we would have a
very bad
situation. It would be awfully hard to explain to them that it
wasn't the
other guy," Worden pointed out.
Similarly, a fireball-caused blast over Tel Aviv or Islamabad
"could be
easily confused as a nuclear detonation and it may trigger a
war," Worden
said.
Meanwhile, now moving through the U.S. Defense Department
circles, Worden
added, is a study delving into issues of possibly setting up an
asteroid
warning system. That system could find a home within the Cheyenne
Mountain
Complex outside Colorado Springs, Colorado. The complex is the
nerve center
for the North American Aerospace Defense Command (NORAD) and
United States
Space Command missions.
Next steps
Where do we go from here?
An important step, Worden said, is cataloging all of the objects
that are
potentially threatening, down to those small objects that could
hit and
destroy a city. To do this type of charting, military strategists
now
champion a space-based network of sensors that keep an eye on
Earth-circling
satellites. These same space sentinels could serve double-time
and detect
small asteroids, he said.
Secondly, more money should be applied to building
microsatellites. Some of
these tiny craft might be placed in a kind of sleep mode - put in
parking
orbits and ready to spring into action in the event of a
intimidating
intruder of the asteroid kind.
For one, these microsatellites can offer "up-close and
personal" looks at
menacing objects. Is an asteroid, for example, solid rock or
rubble pile?
The answer would make a big difference in dealing with an object
having
Earth's name on it. These microsatellites could ram an object
too, adding
extra energy to the body and putting it on an out-of-harms-way
trajectory.
"Before we start detonating nuclear weapons in space to move
something, we
ought to think long and hard how we really want to do this,"
Worden said. "A
lot of folks believe the next step for NASA is not go back to the
Moon or on
to Mars, but go to the asteroids. That's something we ought to be
thinking
about," he added.
Asteroids are interesting from a scientific and space
industrialization
basis, as well as being a threat, Worden said.
"For fear...for greed...for curiosity. Asteroids are about
the only thing in
space that combine all three of those," Worden concluded.
Unlike the dinosaurs
Advancements are being made to take the edge off impact hazard
worry, said
Clark Chapman, planetary scientist at the Southwest Research
Institute in
Boulder, Colorado.
"For one, to mitigate impact hazard is simply to hunt for
them. In hunting
for them, first we learn that many of the objects aren't going to
hit the
Earth. In fact, none of them that we've found so far, that are
large, are
going to hit the Earth," Chapman said.
Chapman said that while the impact hazard from large objects is
real, it is
very unlikely to happen in our lifetimes. He remarked that he
wasn't sure
the logic is in favor of ramping up efforts to search for every
object that
might cause a smaller, Tunguska-like blast.
Underscoring the demolition stemming from a mega-Earth impactor,
Chapman
said that, indeed, the "potential consequences are horrific,
exceeding any
other natural hazard and roughly that of an all-out nuclear
war." Nations do
have the wherewithal to avert a threatening impact, he said.
"Unlike the dinosaurs, the big picture is that we do have
the capability and
intelligence to protect ourselves from this threat. The questions
are...will
we take a gamble and submit to fate? Or do we undertake a
measured,
rationale response? The first element is to educate ourselves and
our
leaders about this issue, and rationally decide what fraction of
our budget
should be devoted to protecting our planet," Chapman said.
Lingering hazard
Chapman emphasized that once all the asteroids have been located,
comets
remain a "lingering hazard." They can creep into our
solar system on short
notice.
Comet Hale-Bopp -- slipping by Earth in 1997 -- was likely 100
times more
massive than the object that wiped out the dinosaurs, Chapman
explained.
"It was a big one, and it was only discovered something like
a year before
it came in," Chapman said.
There is a current dilemma, the planetary scientist added.
In the event a hostile object is on a collision course with our
home planet,
who does the astronomer call? Furthermore, the existing
infrastructure
within which to communicate, then do something about the
troubling impactor,
is very disorganized, Chapman emphasized.
"Astronomers are just learning how to communicate. But the
relevant agencies
are not prepared to listen and act," Chapman said.
Round-trip rockfest
A top priority on the "to do" list of future space
projects is a "hands-on"
near-Earth asteroid (NEA) mission. That's the belief of planetary
scientist,
Daniel Durda of the Southwest Research Institute in Boulder,
Colorado.
Asteroids are "tempting targets" for human explorers,
he said.
Durda points out that there are about 10,000 near-Earth asteroids
larger
than 33 feet (10 meters) across - and they are easier to reach
from an
orbital energy standpoint than the surface of the Moon.
"That suggests that
there should be many launch opportunities over the course of any
given
year," he said.
One prime piece of unreal estate for human exploration, Durda
said, is
asteroid 1991 VG. It passed about 1.2 lunar distances of Earth in
December
of 1991. The orbit of this tiny world is very Earth-like.
Outbound and return trek times involving asteroid 1991 VG would
each be in
the neighborhood of 15 days. Once at the body, a crew could study
the space
rock for 30 days. The entire mission would take about two months,
"well
within our experience base when you consider the stay times that
we become
accustomed to for International Space Station (ISS)
expeditions," Durda
said.
"It turns out that during the entire mission, the crew would
never venture
farther from Earth than about 4.5 lunar distances. The Earth
would never
appear smaller in the sky than the full Moon appears to us from
here on
Earth! That's not such a daunting trip at all," Durda
remarked.
Cling ons
Once a crew is on-location at an asteroid, it's not a cakewalk.
Because of the very low surface gravity of a small asteroid --
even one
under a mile (1-kilometer) in diameter sports a gravity only
1/28000th that
of Earth -- operations in the vicinity of a NEA would be more
like docking
with and spacewalking around the ISS.
In that sense, Durda said, the experience base we are gaining
with space
station hookups and crew members moving about outside the complex
are
invaluable. Also, the rapidly changing orbital day-night lighting
conditions
are similar to what an astronaut would experience on a small,
rapidly
rotating asteroid.
"However, we still need to learn a great deal about
interacting with the
surface of a small asteroid in essentially non-existent
gravity," Durda
said. For instance, he added, how will electrostatically charged
dust from
an asteroid's surface cling to space suits and equipment? How
might we need
to alter or redesign maneuvering backpacks for extended
transportation and
navigation around the rocky world?
There are many benefits from visiting a giant hunk of space
flotsam.
"The NEAs provide the ideal means to expand our experience
base and our
presence beyond low-Earth orbit and beyond the Earth-Moon
system," Durda
said. Asteroid journeys would provide a bonanza of data useful to
asteroid
and meteorite science.
"Development of an asteroid visit capability will also give
us invaluable
data and skills to develop credible deflection and or destruction
technologies for dealing with the asteroid impact hazard,"
Durda concluded.
Copyright 2002, Space.com
===========
(2) SCIENTISTS STUDY DEFENDING EARTH AGAINST ASTEROIDS
>From Scripps Howard News Service, 3 June 2002
http://www.knoxstudio.com/shns/story.cfm?pk=ASTEROIDS-06-03-02&cat=AS
By MICHAEL WOODS
Toledo Blade
June 03, 2002
The federal government is summoning the world's top scientists to
an urgent
conference this summer to plan defenses against an attack that
could wipe
out an American city or disrupt the whole country's
infrastructure.
No, it's not global terrorism.
The scientists will map ways to combat an asteroid attack, a
cosmic sucker
punch like the collision that killed the dinosaurs 65 million
years ago and
flattened a Siberian forest in 1908.
While the world's attention is focused on the real threat of
terrorism, the
theoretical asteroid menace has been garnering a surprising
amount of
behind-the-scenes attention.
Britain's Royal Astronomical Society hosted an international
meeting of
experts on the asteroid impact threat in December. In January the
world's
astronomers petitioned Australia's government to fund a special
asteroid-detecting telescope. In February NASA announced the
"Workshop on
Scientific Requirements for Mitigation of Hazardous Comets and
Asteroids,"
which will be conducted in Washington in September. In March,
NASA activated
"Sentry," a new system to monitor s near-Earth objects
(NEOs) and assess
their threat to Earth.
NEOs are small objects - asteroids and certain comets - that
orbit in the
solar system relatively close to Earth and could one day collide
with Earth.
"We've had a couple of close shaves during the past few
months," said Dr.
Brian G. Marsden, with the Harvard-Smithsonian Center for
Astrophysics in
Cambridge, Mass.
One asteroid caused public jitters when discovered March 12.
Named 2002 EM7,
it came from the direction of the sun - an astronomical blind
spot where
objects are hidden in the sun's glare.
Astronomers didn't detect 2002 EM7 until four days after it came
within
288,000 miles of Earth, which they regarded as a close encounter.
The asteroid was about 200 feet in diameter - big enough to fill
two-thirds
of a football field - and could have flattened a city, unleashing
the energy
of a 5-megaton nuclear bomb.
"I think Mother Nature has given us yet another wake-up
call," said Dr.
Donald K. Yeomans of NASA. "Objects the size of 2002 EM7
pass as close as
this one did every two weeks or so. We just haven't found them
all yet."
Another scare occurred in January, when a 1,000-foot-diameter
asteroid came
within 375,000 miles of Earth. Astronomers detected the
mountain-sized rock,
named 2001 YB5, only a few weeks earlier.
Dr. Richard P. Binzel, with the Massachusetts Institute of
Technology, said
the public can expect more close-encounter stories. "It is
simply a matter
of our increasing prowess in detection that objects like 2001 YB5
are now
being seen," Binzel said.
NASA, the European Space Agency, and universities have been
monitoring space
for NEOs and tracking their paths with great precision.
Astronomers are
detecting more and more asteroids that sped by unnoticed in the
past.
"The goal is to track NEOs well in advance of any
Earth-threatening
encounters so that a mitigation plan could be put into
effect," said
Yeomans, with NASA's Jet Propulsion Laboratory in Pasadena,
Calif. "No
objects that we know about threaten us, and we're well on the way
to finding
the majority of the entire population of large NEOs."
Finding the smaller ones, like 2002 EM7, will take years longer
and require
bigger telescopes than those used in asteroid search-and-tracking
efforts,
he added.
"That said, NEOs are not something to lose sleep over,"
Yeomans added.
Dr. Gareth Williams of the Smithsonian center cited the
importance of
detecting small asteroids when they're visible - not hidden in
the sun's
glare - so they can be tracked and monitored.
Objects the size of 2002 EM7 make similarly close approaches to
Earth
several times a month, Williams said. They hit Earth every 30 to
100 years,
he said, but usually burn up in the atmosphere.
Such impacts, however, create an "air-burst," or
powerful shock wave that
can cause considerable localized damage on the ground below.
"The 1908 Tunguska event was an example of the local damage
that would occur
under and around the air-burst of such an object," Williams
explained,
referring to the incident near the Stony Tunguska River in
Siberia in which
a mysterious airborne explosion - now believed to be an asteroid
impact -
leveled a section of forest half the size of Rhode Island.
Scientists
estimate it caused as much destruction as a 15-megaton nuclear
bomb.
"Impacts by such objects are not likely to cause major loss
of human life,"
Williams asserted. "About 70 percent of the world's surface
is water, and
much of the land mass is either uninhabited or very sparsely
populated."
Using the 1,000-foot diameter 2000 YB5 asteroid as an
illustration, Binzel
said there is about a 1-in-10,000 chance of an impact with Earth
each year
or a 1-in-100 chance of an impact sometime during the 21st
century.
Binzel said 2000 YB5 and 2002 EM7 were essentially no-risk
asteroids.
"Most of these chances are in the 1-in-a-million or
1-in-a-billion range,"
Marsden said. "And it is very likely that that, as we make
further
observations, the impact probabilities will become precisely
zero."
The only nightmare near-Earth object known today is 2002 CU11,
which is
about 2,000 feet in diameter and has a 1-in-9,000 chance of
hitting Earth on
Aug. 31, 2049. It was discovered in February. Scientists think
there are at
least eight other Earth-impact possibilities between 2032 and
2096.
NASA described its September conference as "urgent"
because scientists
believe it will take 70 years to develop mitigation technology
and learn to
use it against an Earth-threatening object. Experts will propose
and discuss
specific countermeasures in September.
"The more we know about NEOs, and the longer the advance
notice of possible
impacts, the better off we are," said Marsden. "We can
do it," he added.
"Pity the poor dinosaurs, who couldn't."
On the Web: Forecasts of known asteroid encounters are easily
available on
the Internet as well, including sites like the NASA-affiliated
www.spaceweather.com.
(Distributed by Scripps Howard News Service, http://www.shns.com .)
===============
(3) STUDY: "PERMIAN-TRIASSIC MASS EXTINCTION NO CAUSED BY
COSMIC IMPACT"
>From CNN, 6 June 2002
http://www.cnn.com/2002/TECH/science/06/06/volcanic.extinction.ap/index.html
WASHINGTON (AP) -- A massive flow of molten rock, bubbling to the
surface
and spreading more than a mile deep over an area half the size of
Australia,
may have killed up to 90 percent of all animal species on Earth
some 250
million years ago, a study suggests.
The study shows that the flood of molten rock that created what
is known as
the Siberian Traps in Russia was almost twice as big as
previously believed
and could have continued for thousands of years, changing the
climate of the
entire planet.
The researchers, a group of United Kingdom and Russian
scientists, say in a
report to appear Friday in the journal Science that such an
eruption of
flood basalt would have filled the atmosphere with a choking
concentration
of sulfur dioxide, carbon dioxide and other gasses, making it
difficult for
any species to survive.
Samples from the lava flow have been age-dated at about 250
million years.
Other studies have shown during this same period the Earth
experienced its
most extensive extinction crisis -- a die-off that killed at
least 90
percent of ocean species and more than 70 percent of land
creatures.
Called the Permian-Triassic extinction, it is a key event in the
history of
the planet. It was followed by the rise of the dinosaurs, the
animal species
that dominated the Earth, until they too went extinct about 65
million years
ago.
In the study, the researchers analyzed samples drilled from deep
below the
floor of a basin beside the known Siberian Traps. They found that
the basin
was underlain with the same type and age of lava that created the
Traps.
This means that the flood of lava that formed the Traps was at
least twice
as massive and lasted perhaps twice as long as previously
believed, they
said.
Asteroid theory
Such a large volume of lava spewing to the surface over hundreds
of
thousands of years would inject millions of tons of chemicals
into the
atmosphere, causing long-lasting changes in the climate and an
ecological
collapse, they said.
"The larger area of volcanism strengthens the link between
the volcanism and
the end-Permian mass extinction," the authors say in
Science.
Some earlier studies have suggested that the Permian-Triassic
extinction was
caused by an asteroid striking the Earth and wiping out much of
life with a
sudden, single stroke.
But the evidence from the new study points toward a prolonged
extinction
event, stretching over hundreds of thousands of years.
Peter D. Ward, professor of geological sciences and a
paleontologist at the
University of Washington, said the United Kingdom and Russian
study
reinforces what is becoming a widely accepted view of many other
researchers.
"It looks like the Earth was getting multiple levels of
extinction," said
Ward. He said chemical studies of ancient geology suggest that
plant
productivity was impacted "over and over again" during
the period around the
Permian-Triassic boundary.
'Not a single event'
He said phased cycles of extinction, as evidenced in the
geological record,
are compatible with a massive, prolonged flood of molten basalt.
"We don't see all of the basalt coming out at once, as a
steady stream,"
said Ward. "It was not a single event" such as an
asteroid impact.
This is in contrast to the extinction event that killed the
dinosaurs. Ward
said many different studies show that an asteroid did deliver
"a one-time
hit" on the Earth that caused rapid changes that snuffed out
the dinosaurs.
Marc K. Reichow of the University of Leicester in the United
Kingdom was
lead author of the study. Other researchers were from the
Scottish
Universities Environmental Research Center in Scotland, and from
the
Institute of Geochemistry and the Institute of Geology Oil and
Gas, both in
Russia.
Copyright 2002 The Associated Press.
=============
(4) FORGET NEO IMPACTS: "VOLCANOES KILLED OFF PERMIAN
SPECIES"
>From Nature, 7 June 2002
http://www.nature.com/nsu/020603/020603-6.html
Lava flow twice the size of Europe covered Siberia 250 million
years ago.
PHILIP BALL
We knew it was big - but not this big. Geologists now suspect the
massive
eruption of lava in Siberia 250 million years ago was at least
twice as
large as they'd thought. This makes it even more likely to have
caused the
biggest extinction the world has ever seen.
The Permian period ended with the extinction of 85% of all ocean
creatures
and 70% of land ones - a toll three times greater than the
extinction that
killed off the dinosaurs at the end of the Cretaceous, 65 million
years ago.
At the same time Siberia was flooded with at least a million
cubic
kilometres of lava. Scientists have wondered for years whether
the two were
related.
Very probably, say Andrew Saunders of the University of Leicester
in the UK
and co-workers. They have found that the Siberian flood basalt
province
extends much farther west than previously analyses suggested.
Lava, arising from deep within the Earth, brings up with it huge
amounts of
gases such as sulphur dioxide, carbon dioxide and hydrogen
fluoride.
Released into the atmosphere, these gases can drastically change
environmental and climatic conditions. Sulphur dioxide, for
instance, is
poisonous and creates acid rain. Carbon dioxide is a greenhouse
gas.
Ash and sulphur gases can also create airborne particles that
block out
sunlight, cooling the Earth's surface. There is evidence that sea
level
plummeted at the end of the Permian - possibly as a result of an
expansion
of the ice sheets.
No one knows exactly how big these effects might have been, or
how they
might have affected life on the planet. But they could have
caused the kind
of disruptions to ecosystems that tip species towards extinction.
Under Traps
The Siberian Traps are a plain of volcanic rock stretching for
over 1,000 km
from north to south. Centred around the city of Tura, the Traps
cover around
2 million square kilometres: more than the entire land surface of
Europe.
Saunders's team bored holes more than 4 km deep into the West
Siberian
Basin, to the west of the Traps. The researchers found yet more
basalt
hidden deep below these rocks.
They calculate that the buried basalt is 249 million years old -
the same
age as that in the Traps. It is more material from the Siberian
Traps, they
reason, which later became flooded and buried.
The researchers estimate that the buried basalt covers at least
as great an
area, and contains as great a volume, as the exposed Siberian
Traps to the
east. In other words, the vast outpouring of lava at the end of
the Permian
was twice as extensive as previously thought, maybe even more.
Cloud cover
A more speculative explanation for mass extinctions has also been
put
forward this week. Hans Jorg Fahr of the Bonn Institute of
Astrophysics and
Extraterrestrial Research in Germany and colleagues propose that,
on its
orbit around the centre of the Galaxy, our Solar System passes
once every 60
million years or so through dense clouds of interstellar gas.
This, the
researchers believe, could disrupt the solar wind, the stream of
charged
particles from the Sun.
The solar wind shields the Earth from cosmic rays. If the wind
weakens, more
cosmic rays break through into the Earth's atmosphere and collide
with air
molecules to produce electrically charged fragments. These
fragments trigger
the formation of cloud droplets. The resulting change in cloud
cover could
alter climate in ways that lead to mass extinctions, Fahr and his
team
reason.
But it is unclear whether the effects of greater cloudiness could
be that
dramatic, and it is far from certain that mass extinctions really
show a
60-million-year periodicity.
References
Reichow, M. K. et al. 40Ar/39Ar dates on basalts from the West
Siberian
Basin: doubled extent of the Siberian flood basalt province.
Science, 296,
1846 - 1849, (2002).
Copyright 2002, Nature News Service / Macmillan Magazines Ltd
2002
================
(5) FLOOD BASALT: BIGGER AND BADDER
>From Science, 7 June 2002
http://www.sciencemag.org/cgi/content/full/296/5574/1812
Paul R. Renne [HN17]*
Flood volcanism [HN1] is an episodic process whereby vast amounts
of mass
and energy are transferred from Earth's interior to its surface
within a
relatively short time. Such events have occurred about a
dozen times during
the last several hundred million years. There is increasing
geochronological
[HN2] evidence that in each of these events, the magma [HN3] was
generated
and erupted within 1 to 3 million years or so. The implied magma
production
rate, on the order of 106 km3/year, is much higher than in
Earth's main
magma-producing environments at the boundaries between
lithospheric plates.
Increasingly, Earth scientists are trying to establish the causes
and
consequences of flood volcanism. The Siberian Traps [HN4] have
played a
central role in shaping thought on the problem.
More than 20 years ago, Morgan [HN5] (1) posited that this
massive mantle
belch might have been the first manifestation of a still-active
magma source
(hot spot) represented by a volcanic island, Jan Mayen
[HN6], in the North
Atlantic. A generalized theory soon linked flood basalts to hot
spots
created by buoyant, superheated mantle plumes, which were
inferred to play
a dynamic role in the rifting apart of continents [HN7] (2). A
leading
alternative to these "plume impact" models holds that
flood volcanism
results when rifting of the lithosphere causes
decompression of the mantle,
allowing it to melt and rise buoyantly without requiring
anomalous heating.
The rifting that precedes decompression melting in the latter
model cannot
happen quickly for mechanical reasons: The lower
lithosphere is ductile and
does not break rapidly under extension. Pure decompression
melting therefore
seems less consistent with the observed rapidity of the eruptions
than does
the plume impact model. On the other hand, there is evidence that
crustal
extension predates volcanism in some cases, which suggests that
at least
some aspects of the decompression model are valid. But what
initiates
extension, if not the dynamic consequences of plume impact? One
possibility
is edge-driven convection (3), hypothesized to originate
from
discontinuities in lithospheric thickness and properties.
Besides establishing the brevity of flood volcanic events,
geochronology has
played a key role in defining the vast provinces wherein
they occur. A
recent example is the central Atlantic magmatic province (CAMP)
[HN8], whose
200-million-year-old remnants are now scattered across eastern
North
America, northeastern South America, western Africa, and western
Europe. It
had been hypothesized that CAMP's remnants formed a single
contiguous
province before the opening of the central Atlantic (4), but it
was only
through precise dating of the dispersed fragments that
identification of an
extensive flood basalt province was confirmed (5).
Similarly, new dating results reported by Reichow et al. [HN9] on
page 1846
of this issue (6) document the subsurface extent of the Siberian
Traps
nearly 1000 km westward from the previously known limits of the
province.
The authors have analyzed drill-core samples from the West
Siberian Basin
[HN10] (WSB). The new dating provides the first definitive
evidence linking
them to the same magmatic event.
Using the 40Ar/39Ar method [HN11], Reichow et al. (6) show that
the WSB
lavas are indistinguishable in age from those to the east,
previously dated
at 250 million years by similar methods (7). The new results
suggest a total
areal extent of 3.9 x 106 km2 for the Siberian Traps. The total
volume of
magma represented by this enlarged province is difficult to
estimate, but 2
x 106 to 3 x 106 km3 is probable, clearly qualifying the
Siberian Traps as
the largest (by volume) known continental flood basalt province.
The WSB underwent rifting during the late Paleozoic or early
Mesozoic (about
300 to 200 million years ago), bearing out the general
relationship between
extension and flood volcanism. Unfortunately, as in many other
cases,
existing data appear equivocal on the crucial question
of whether extension began before or after the onset of
volcanism.
Establishing the relative ages of these events should now become
a priority.
Upward revision of the dimensions of flood volcanic provinces
will doubtless
continue as research progresses. Recent work (8) shows that
magmatism of
essentially the same age as the Siberian Traps occurred as far
south as
central Kazakhstan, and a swath of contemporary magmatic activity
may even
extend semicontinuously from there to south of Lake Baikal. These
complexes
appear to represent the roots of silicic volcanic centers, whose
explosive
eruptions would have provided a mechanism for transporting
volcanogenic
gases [HN12] into the upper atmosphere.
These increasing size estimates have important implications for
the
environmental consequences of flood volcanic events. The more
voluminous a
magma system is, the more likely it is to generate large
quantities of
climate-modifying gases such as CO2 and SO2. The amounts of such
gases
actually delivered to the atmosphere by flood volcanism remain
difficult to
quantify, but there is little doubt that the effects could be
significant.
The synchrony between flood volcanic events and mass
extinctions [HN13] in
the geologic record has been noted for years. For the three
biggest events
(the Siberian, CAMP, and Deccan traps [HN14]), a temporal
correlation with
the most severe extinctions at the end of the Permian, Triassic,
and
Cretaceous periods, respectively, is firmly established.
The empirical connection between major flood volcanism and severe
mass
extinctions is all the more intriguing in light of hints of
evidence of
large meteor impacts coincident with these events. The evidence
is strongest
at the end of the Cretaceous. The latest hint suggests that
CAMP and the extinction at the end of the Triassic may have been
coincident
with an impact [HN15] (9), although the impact evidence in this
case is
permissive rather than indicative.
To some Earth scientists, the need for a geophysically plausible
unifying
theory linking all three phenomena is already clear. Others still
consider
the evidence for impacts coincident with major extinctions too
weak, except
at the end of the Cretaceous. But few would dispute that proving
the
existence of an impact is far more challenging than documenting a
flood
basalt event: It is difficult to hide millions of cubic
kilometers of
lavas--even, as shown by Reichow et al. (6), when they are buried
beneath 2
km or more of sediments in Siberia.
References and Notes
1.W. J. Morgan, in The Sea, C. Emiliani, Ed. (Wiley-Interscience,
New York,
1981), vol. 7, pp. 443-475.
2.M. A. Richards, R. A. Duncan, V. E. Courtillot, Science 246,
103 (1989)
[GEOREF] [JSTOR].
3.S. D. King, D. L. Anderson, Earth Planet. Sci. Lett. 160, 289
(1998)
[ADS].
4.V. Courtillot, Isr. J. Earth Sci. 43, 255 (1994) [GEOREF].
5.A. Marzoli et al., Science 284, 616 (1999).
6.M. K. Reichow et al., Science 296, 1846 (2002).
7.Originally dated at about 248 Ma (10), these ages were revised
after
recalibration of a standard (11).
8.J. O. Lyons et al., J. Geophys. Res., in press.
9.P. E. Olsen et al., Science 296, 1305 (2002).
10.P. R. Renne, A. R. Basu, Science 253, 176 (1991) [GEOREF]
[JSTOR].
11.P. R. Renne et al., Science 269, 1413 (1995) [GEOREF] [JSTOR].
The author is at the Berkeley Geochronology Center, Berkeley, CA
94709, USA,
and in the Department of Earth and Planetary Science, University
of
California, Berkeley, CA 94720, USA. E-mail: prenne@bgc.org
Volume 296, Number 5574, Issue of 7 Jun 2002, pp. 1812-1813.
Copyright © 2002 by The American Association for the Advancement
of Science.
All rights reserved.
=============
(6) FORGET NEO IMPACTS: "COSMIC STORM KILLED OFF
DINOSAURS"
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
Universität Bonn
Bonn, Germany
Contact:
Professor Hans Jörg Fahr
Institute of Astrophysics and Extraterrestrial Research
hfahr@astro.uni-bonn.de,
++49-228-733677
Dr. Michael Bird
Institute of Radio Astronomy
++49-228-733651
4 June 2002
Protective Storm in Space -- a new explanation for the death of
the
dinosaurs
A shower of matter from space millions of years ago could have
led to
drastic changes in the Earth's climate, followed by the
extinction of life
on a massive scale, which also killed off the dinosaurs. This at
least is a
theory put forward by scientists from the University of Bonn.
Normally, the
solar wind acts as a shield against showers of cosmic particles,
which
prevents too many energy-rich particles from raining down on our
atmosphere.
Since 1997 scientists from Bonn, funded by the German Research
Council
(Deutsche Forschungsgemeinschaft or DFG), have been examining how
and
why this gigantic shield works.
They were the undisputed masters of a whole geological era until
they
suddenly disappeared 65 million years ago. "Perhaps Earth
just became too
damp and too cold for dinosaurs at that time," Professor
Hans Jörg Fahr from
the Bonn Institute of Astrophysics and Extraterrestrial Research
surmises.
The reason for the sudden change in climate could have been
excessive
pressure on our cosmic umbrella.
The solar system does not stand still, in fact it orbits the
centre of the
Milky Way once every 250 million years. In the process it also
passes
through dense clouds of interstellar matter, which causes
problems for the
solar wind and thus for the Earth. Whereas the solar wind
normally protects
the Earth from a hail of interstellar particles like a huge
bullet-proof
vest, there are then suddenly up to a hundred times more
particles raining
down into the earth's atmosphere at enormous speeds. On impact
they smash
the air molecules into electrically charged fragments. These
function as
condensation nuclei on which droplets of water form. "The
result is dense
cloud cover with greater precipitation and sinking
temperatures," says Professor
Fahr, who bases his remarks on research worldwide.
Prof. Fahr and his colleagues Dr. Horst Fichtner and Dr. Klaus
Scherer have
shown that every 60 million years on average the solar system
passes through
dense clouds of matter, which could trigger off this sort of
climate shock.
Prof. Fahr adds: "At roughly these intervals many species
suddenly became
extinct." Research by other teams which have examined the
link between cloud
cover and solar activity has shown that cosmic factors could have
had a dramatic impact
on our climate on several occasions in the past. "The less
solar activity there is
and therefore the less protection there is from the solar wind,
the more
cosmic particles reach the earth, and the more clouds form on
earth," is how
Prof. Fahr sums up the process.
Experts call the electrically charged particles which our sun
emits "solar
wind". They race through our solar system at a velocity of
up to 800
kilometres per second, with a range extending a hundred times as
far as the
distance between the Earth and the sun. "Every eleven years
the sun's
activity and therefore the solar wind reaches a maximum. At these
times, for
example, there is an increase in the frequency of the colourful
auroras, when particles of
the solar wind are captured by the Earth's magnetic field and are
then catapulted into the
upper atmosphere, where they make the oxygen glow," Dr.
Michael Bird from
the Institute of Radio Astronomy explains. During particularly
active
phases, e.g. during big solar eruptions, the shower of particles
can even
interfere with short-wave reception, disrupt orbiting satellites
or even
"switch off" whole power stations.
"In Bonn we are especially interested in how the solar wind
reaches its high
velocities," Dr. Bird explains. "These cannot be
explained solely by the
enormous heat in the sun's atmosphere." There seems, in
other words, to be
another source of energy which catapults the particles into
space. The hot
favourites for Bonn's astrophysicists are exotic waves of
magnetic fields in
the corona, the "sun's atmosphere" which are amplified
while they are
expanding and then give the particles the necessary momentum.
"We are
tracking these waves by using radio astronomy," the US
physicist adds.
Incidentally, cosmic weather might also be a decisive factor in
the speed of
evolution. The cosmic rays from which we are protected by the
solar wind are
so full of energy that they can change the DNA of living beings.
If the
solar wind's shield effect is too weak, i.e. the Earth's
protective mantle
is thin, within a short space of time this results in more
mutations, which
are the driving force of the evolution of life.
Notes for editor:
Pictures to this press release are by 2 p.m. available in the
web:
http://www.uni-bonn.de/Aktuelles/Pressemitteilungen/177_02.html
=============
(7) PERMIAN IMPACT CAUSED LARGEST MASS EXTINCTION ON EARTH
>From Space Daily, 31 August 2001
http://www.spacedaily.com/news/life-01ze.html
Boulder - August 30 2001
What actually ended the Permian Period some 251 million years
ago? Most
Earth scientists think gradual sea fall, climate change, oceanic
anoxia, and
volcanism were the causes.
But that's not so. A group of geologists working in southern
China found
evidence that it was an asteroid or a comet that smacked our
planet,
exploded, and then caused the most severe biotic crisis in the
history of
life on Earth.
In the September issue of Geology, Kunio Kaiho from Tohoku
University
reports their findings of a remarkable sulfur and strontium
isotope
excursion at the end of the Permian, along with a coincident
concentration
of impact- metamorphosed grains and kaolinite and a significant
decrease in
manganese, phosphorous, calcium, and microfossils (foraminifera).
Their discoveries at Meishan (Mei Mountain) suggest that an
asteroid or a
comet hit the ocean at the end of the Permian, triggered a rapid
and massive
release of sulfur from the mantle to the ocean-atmosphere system,
swooped up
a significant amount of oxygen, precipitated acid rain, and
possibly set off
large-scale volcanism.
"Understanding the cause of this event is important because
it represents
the largest mass extinction," Kaiho said, "and it led
to the subsequent
origination of recent biota on Earth."
Kaiho discovered the significance of the site when he took
samples from it
in 1996 and again in 1998. He plans to investigate other evidence
of impact
events.
"We would like to clarify paleoenvironmental changes and
causes of the end
Permian mass extinction in different places and of the other mass
extinctions which occurred during the past 500 million years: end
Ordovician, Late Devonian, and end Triassic," he said.
===========
(8) AN EXTRATERRESTRIAL IMPACT AT THE PERMIAN-TRIASSIC BOUNDARY?
>From Science, Volume 293, Number 5539, Issue of 28 Sep 2001,
p. 2343.
An Extraterrestrial Impact at the Permian-Triassic Boundary?
Becker et al. (1) presented geochemical evidence
that suggests that
the largest mass extinction in Earth history, at the
Permian-Triassic
boundary (PTB) 250 million years ago (Ma), coincided
with an
extraterrestrial impact comparable in size to the
one that likely
caused the end-Cretaceous extinctions 65 Ma (2).
Although Becker et
al. analyzed material from sections in Hungary,
Japan, and China, the
Hungarian section yielded no extraterrestrial
signature, and their
identification of the PTB in the Japanese section is
questioned in the
accompanying comment by Isozaki (below). Thus, only
their analyses of
the Chinese section provide hitherto uncontested
evidence for an
impact at the boundary--in the form of data on the
abundance and
composition of fullerenes in the "boundary
clay," a volcanic ash layer
called Bed 25 at Meishan, China (3). Although
fullerenes may be purely
terrestrial [see, e.g., (4)], Becker et al. report
that the fullerenes
from the Meishan ash carry extraterrestrial noble
gases in the cage
structure, rich in 3He and with distinctive 3He/36Ar
and 40Ar/36Ar
ratios, and that this signature therefore derived
from a bolide
impact. Here, we report that we are able to detect
fullerene-hosted
extraterrestrial 3He neither in aliquots of the same
Meishan material
analyzed by Becker et al., nor any in samples of a
second Chinese PTB
section, and that we thus find no evidence for an
impact.
Becker et al. reported helium in bulk rock and in
fullerenes extracted
from Meishan Bed 25 following acid demineralization.
Their two
aliquots of bulk rock yielded 0.43 and 0.58 pcc/g
(10 - 12 cc g - 1 at
standard temperature and pressure) of 3He. From 40 g
of rock, Becker
et al. extracted 14 µg of fullerene that yielded
very high 3He
concentrations, implying that fullerene-hosted
helium accounted for at
least 0.052 pcc/g of the 3He in Bed 25; this number
could be higher,
because Becker et al. provided no indication of
fullerene extraction
efficiency.
We first analyzed 15 aliquots of bulk rock from Bed
25, provided by
S. Bowring to be representative of the material he
supplied to Becker
et al. Samples were initially dried in an oven for 2
hours at ~90 to
100 °C to drive off adsorbed water. Based on
stepped-heating results
on fullerenes (1), no 3He would have been lost
during sample drying.
We then gently powdered 150 g of rock by hand with a
mortar and pestle
and thoroughly homogenized the sample. Ten aliquots
(~350 mg each)
were drawn from this homogenized powder; the
remaining five aliquots
were taken from several different clumps of the
material to assess
spatial heterogeneity. Samples were fused under
vacuum at 1400°C
following procedures reported earlier (5), except
that the acetic acid
step, designed to remove CaCO3, was not used on
these carbonate-poor
rocks. None of these samples yielded a significant
amount of 3He (Fig.
1): The mean of the 15 runs was 0.005 pcc/g, and the
maximum for any
single aliquot was only 0.01 pcc/g. We obtained
similar results from
six samples of the stratigraphically equivalent bed
at Shangsi, China
(also provided by Bowring). Hence, we obtained 3He
concentrations from
bulk rock samples that were a factor of 45 to 150
lower than those
reported by Becker et al. To ensure that we were
quantitatively
extracting all the He at 1400°C, we outgassed a
single sample at
1800°C after fusion at 1400°C; no additional 3He
was released.
Fig. 1. He isotope data for Chinese PTB samples.
Filled symbols, Becker et al. (1); open symbols,
this study.
We then demineralized a 16 g aliquot of Meishan Bed
25, following the
same HF-BF3 digestion procedure (6) used by Becker
et al. This residue
contained only 0.003 pcc of 3He per gram of starting
material. Because
the demineralized residue does not contain
significant 3He,
fullerene-hosted 3He within this residue cannot be
significant either,
so we did not isolate fullerene for noble gas
analysis. This
experiment places an upper limit on the
fullerene-hosted 3He in Bed
25 that is a factor of 15 lower than the
concentration reported by
Becker et al. (1).
The helium we obtained from Bed 25 samples is
reasonable for a
250-million-year-old volcanic ash bed. Large
inter-aliquot variability
in 4He content and the survival of most 4He through
HF
demineralization (Fig. 1) suggest that accessory
zircons, known to
exist in Bed 25 (3), control the distribution of
this isotope. The 3He
concentration and 3He/4He ratio (average <0.003
RA) of Bed 25 are
lower than we obtained from several hundred deep-sea
carbonate
sediments [see, e.g., (5)] and are at the low end of
the range
expected for purely terrestrial radioactive decay
processes (7). The
dearth of 3He from interplanetary dust particles
(IDPs)--not to be
confused with a fullerene-hosted impact
signature--is not surprising,
because Bed 25 is a volcanic ash and was likely
deposited quickly.
We thus find no evidence for the impact-derived 3He
reported by Becker
et al. Our analytical technique for 3He is as
sensitive and precise
[see details in (5)] as that used by Becker et al.,
so the discrepancy
between our results and theirs is probably not
analytical in origin.
Sample heterogeneity is also an unlikely
explanation: Although Becker
et al. found substantial 3He in all three aliquots
they analyzed (a
total of 41 g of rock), we were unsuccessful in
detecting
extraterrestrial 3He in any of our 22 aliquots (150
g of homogenized
Bed 25 in 10 aliquots, 1.5 g of spatially
distributed spot samples in
five aliquots, and 16 g of demineralized rock in one
aliquot from
Meshian, as well as 2 g of rock in six aliquots from
three samples of
the Shangsi P-Tr boundary bed).
Without confirmation of fullerene-hosted 3He in Bed
25, both the
occurrence of an extraterrestrial impact and the
cause of the mass
extinction at the PTB must remain open questions.
K. A. Farley
S. Mukhopadhyay
Division of Geological and
Planetary Sciences
MS 170-25
California Institute of Technology
Pasadena, CA 91125, USA
E-mail: farley@gps.caltech.edu
REFERENCES
1. L. Becker, R. J. Poreda, A. G. Hunt, T. E. Bunch,
M. Rampino,
Science 291, 1530 (2001).
2. L. W. Alvarez, W. Alvarez, F. Asaro, H. V.
Michel, Science 208,
1095 (1980).
3. S. A. Bowring et al., Science 280, 1039 (1998).
4. D. Heymann et al., Geol. Soc. Am. Spec. Pap. 307,
453 (1996).
5. S. Mukhopadhyay, K. Farley, A. A. Montanari,
Geochim. Cosmochim.
Acta 65, 653 (2001).
6. T. L. Robl and B. H. Davis, Org. Geochem. 20, 249
(1993).
7. J. N. Andrews, Chem. Geol. 49, 339 (1985).
27 April 2001; accepted 17 August 2001
Becker et al. (1) reported an anomaly in 3He trapped
in fullerene from
PTB rocks from Japan and China, which in turn
suggested a possible
extraterrestrial impact as the cause of the PTB mass
extinction.
Although the approach of using the 3He signature
appears promising,
the stratigraphy of the Sasayama section in Japan
poses a major
problem that is fatal to their conclusion: The PTB
horizon is missing
in this section, and the "3He-enriched"
sample they analyzed has
actually come from at least 0.8 m (and possibly much
further) below
the PTB.
Owing to absence of good index fossils, the Sasayama
section is dated
by correlation with other sections. The PTB sections
of deep-sea chert
facies have been examined in more than ten sections
in Japan (2, 3);
all showed a constant lithostratigraphy that
comprised, from bottom to
top, (i) Late Permian bedded chert, (ii) latest
Permian siliceous
claystone or shale, (iii) boundary black organic
claystone, (iv) Early
Triassic siliceous claystone, and (v) late Early to
Middle Triassic
bedded chert. The lower chert and siliceous
claystone are
characterized by Chanhsingian (late Late Permian)
radiolarians such as
Neoalbaillella optima and Albaillella triangularis
(4), and the upper
siliceous claystone and chert contain distinct Early
Triassic forms.
The central black claystone, less than 5 m thick,
yields only
ill-preserved microfossils and thus is not dated
precisely.
Nevertheless, these data indicate that the PTB
horizon is somewhere
within the black claystone (2), not in the lower
siliceous claystone.
Thus the "3He-enriched" sample of Becker
et al. (1) was clearly
collected from the Late Permian interval at least
0.8 m below the PTB.
Making the situation worse, this section is cut in
the middle by a
fault, with gouge and chert breccia [described as
sheared black shale
in figure 2 of (1)] that has removed beds nearly 20
to 30 m thick
between the lower siliceous claystone and the upper
chert. Thus, not
only does the section lack the PTB horizon, but this
faulting has
removed an additional, undetermined interval of time
between the
claimed "3He-enriched" sample and the PTB.
In any case, the Permian
radiolarians and conodonts survived even above this
"3He-enriched"
horizon up to the top of the siliceous claystone.
This suggests that
the alleged impact event did not terminate such
cosmopolitan marine
biota that flourished throughout the Permian and
finally disappeared
at PTB.
At least for confirming the background absence of
3He in adjacent
horizons immediately above and below PTB, Becker et
al. should have
checked better PTB sections and used more samples
collected following
a double-blind protocol. Becker et al. also reported
a similar 3He
spike from Bed 25 (a volcanic tuff of terrestrial
origin) immediately
below PTB in the Meishan section in China. Because
the "3He-enriched"
sample from Sasayama is significantly older than
Meishan Bed 25, they
cannot have been from the same impact event.
Yukio Isozaki
Department of Earth Science and Astronomy
University of Tokyo
Komaba, Tokyo 153-8902, Japan
REFERENCES
1. L. Becker, R. J. Poreda, A. G. Hunt, T. E. Bunch,
M. Rampino,
Science 291, 1530 (2001).
2. Y. Isozaki, Science 276, 235 (1997).
3. Y. Kakuwa, Palaeogeogr. Palaeoclimatol.
Palaeoecol. 121, 35 (1996).
4. K. Kuwahara, S. Nakae, A. Yao, J. Geol. Soc.
Japan 97, 1005 (1991).
2 April 2001; accepted 17 August 2001
Response: In our study (1), we suggested that an
impact event occurred
at the 250-million-year-old PTB, triggering the most
severe mass
extinction in the history of life on Earth. By
exploiting the unique
ability of the fullerene molecule to trap noble
gases inside of its
caged structure, we were able to determine whether
the origin of the
fullerenes was extraterrestrial (ET) or terrestrial.
We have found
fullerenes with ET helium associated with extinction
events in five
locations at the 65-million-year-old
Cretaceous-Tertiary boundary
(KTB) and in two locations at the PTB (1, 2).
Although it has been
suggested that the fullerenes isolated from some KTB
sediments may
have been associated with terrestrial
causes--specifically, with
global wildfires triggered by the impact event--it
has now been
accepted that the KTB fullerenes are
extraterrestrial, delivered
exogenously to the Earth during the impact itself
(3, 4).
Farley and Mukhopadhyay, at Caltech, report that
they have measured
background levels of 3He across the PTB in sections
in Meishan and
Shangsi, China, and have concluded that there is no
evidence for the
delivery of ET material to the Earth by a bolide.
Rather, their
results are consistent with helium present in a
250-million-year-old
ash layer found at both boundary sections. We
observed significant
differences between the procedures we used and those
carried out
during their study, however, and we believe that
these differences
influenced the outcome of their experiments.
In our study, we obtained a ~75-g sample of Bed 25
from S. Bowring
that contained the base of this unit, which
represents the time
interval during which more than 90% of all marine
organisms, most of
the terrestrial vertebrates, and many plants were
brought to an abrupt
extinction (1, 5, 6). Because we were interested in
focusing on this
discrete event rather than looking at the continuous
flux of 3He
throughout Bed 25, we separated out the carbon-rich
basal material,
characterized by an interstratified reddish-gray
montmorillonite-illite clay layer. This reduced our
bulk sample to the
~40 g of material that was demineralized using the
procedures outlined
in (1). The acid residue (442 mg) that represented
about 1% of the
original material was extracted with solvents to
isolate the fullerene
component (14 µg). In contrast, the Bed 25 ash,
provided to us by the
Caltech group, contained less than 0.1% (or 6 mg in
7 g of ash)
acid-resistant residue, and that fraction appeared
to be mostly
resistant silicates such as zircon. Thus, our
contention is that the
Caltech sample contained neither the organic carbon
carrier for the
3He-rich fullerene component nor the carrier
(whatever it may be) for
the bulk 3He or background flux. Our bulk 3He
concentrations in two
aliquots of the PTB sample yielded values of 0.43
and 0.58 pcc/g,
while several samples above and below the boundary
had 3He
concentrations about 10 times lower ( <=
0.02 to 0.2 pcc/g) (7).
To further assess the variability in bulk 3He
measured for the Meishan
samples collected at the boundary (Bed 25) and in
samples directly
above and below this interval, we also obtained a
separate suite of
Meishan samples from S. D'Hondt. The samples
collected by D'Hondt were
evaluated for delta 13C and compared to replicate
samples measured in
(5). This material also represented the changes in
lithology at the
base of Bed 25 and in the sediments above and below.
These samples had
even more 4He (3 to 10 µcc/g) than the samples
measured in either our
study (1) or that of Farley and Mukhopadhyay. In our
case, the high
4He concentrations made it impossible to evaluate
the 3He
concentrations because the 3He/4He ratio was at the
abundance
sensitivity limit. Unfortunately, our samples were
not available for
reassessment of the bulk 3He upon submission of the
comment by Farley
and Mukhopadhyay. We have since reproduced our own
results with four
replicate analyses of the boundary layer. The 3He
concentrations at
the Meishan boundary range from 0.15 to 0.5 pcc/g.
We will also
provide our samples to two separate labs for
independent measurements
of the bulk 3He. We are confident that these labs
will reproduce our
results (1) and will further demonstrate the
differences in the
samples provided by S. Bowring to Caltech and us.
The differences in bulk 3He and 3He fullerene
concentrations appear to
be directly attributable to sample selection and
preparation. By
homogenizing a 150-g sample of volcanic ash, Farley
and Mukhopadhyay
may reduce the variability and noise in the 3He
signature, an
important consideration when examining long-term IDP
flux signals. We
concur with their conclusion that the volcanic ash
would have been
deposited very rapidly and would not preserve the
extraterrestrial
signature attributed to IDPs. However, when
examining "event markers"
such as fallout from a bolide impact, the
homogenization strategy
would severely dilute the already weak 3He signal
present in the bulk
ash. Variations in the carbon content and 3He
concentrations in the
Bed 25 samples clearly point to the fact that the
two groups examined
very different samples. The change in lithology at
the base of Bed
25 apparently makes a significant difference in the
identification of
the bolide event marker, and care must be taken to
identify and
quantify the helium carriers present in the
boundary.
In a separate comment, Isozaki suggests that the
fullerenes we
detected in the siliceous claystone at Sasayama did
not come from the
PTB. Instead, using lithostratigraphy, he places the
true boundary
somewhere within the carbonaceous claystone above
this interval.
However, as pointed out both by Kakuwa (8) and in
Isozaki's comment,
the PTB cannot be precisely defined in any of the
Japanese sections
because of poor stratigraphic control. Moreover,
neither the siliceous
claystone nor the carbonaceous claystone have
age-diagnostic fossils
to properly date the boundary at Sasayama or in any
of the Japanese
sections (8), as the comment by Isozaki
acknowledges.
The principal difference underlying our placement of
the boundary
compared with that of Isozaki rests on the mechanism
that led to the
PTB mass extinction. Isozaki favors a model
involving overturn of
CO2-saturated deep anoxic water, coupled with a
hypothesized
"hypercapnia" that apparently lasted some
20 million years (9). As
pointed out by Gin et al. (5), however, the mass
extinction that
occurred at the PTB was abrupt, lasting only a few
100,000 years. Our
boundary sample, provided by M. Rampino, was
selected based upon
evidence for an extraterrestrial cause (10, 11). So
far, we have only
found fullerene at the boundary, and not in
significant concentrations
above and below (1, 2). Thus, in the absence of any
biostratigraphy
and poor stratigraphic control (8), we feel that the
best
interpretation for the boundary at Sasayama is in
the siliceous
claystone, where fullerene and other
extraterrestrial signatures have
been identified (1, 10, 11).
Perhaps the most significant drawback to our
investigation of the PTB
to date is the lack of geographic spread and the
inability to
demonstrate that other extraterrestrial signatures,
like those
reported in some KTB sites (1), are also present in
the PTB. New
results on sediments collected from the Meishan PTB
show that Fe-Si-Ni
grains are concentrated in the top 2 cm of Bed 24e
and in the
overlying basal portion of Bed 25 (12). These
Fe-Si-Ni grains are
produced at very high temperatures (Fe, 2890oC; Ni,
2863oC; Si,
2227 oC), and are thus inconsistent with a volcanic
origin but
consistent with impact-metamorphosed grains found in
some impact
craters and in sediments associated with the KTB
(12, 13).
Interestingly, some Fe-rich nuggets have also been
reported in the
siliceous claystone at Sasayama (14). Based on these
new results, it
would appear that an impact event of global
proportions remains the
best explanation for the most severe biotic crisis
in the history of
life on Earth.
Luann Becker
Department of Geological Sciences
Institute of Crustal Studies
University of California at Santa Barbara
Santa Barbara, CA 93106, USA
E-mail: lbecker@crustal.ucsb.edu
Robert J. Poreda
Department of Earth and
Environmental Sciences
University of Rochester
Rochester, NY 14627, USA
REFERENCES AND NOTES
1. L. Becker, R. J. Poreda. A. G. Hunt, T. E. Bunch,
M. Rampino,
Science 291, 1530 (2001).
2. L. Becker, R. J. Poreda, T. E. Bunch, Proc. Natl.
Acad. Sci. U.S.A.
97, 2979 (2000).
3. D. Heymann, L. P. F. Chibante, R. R. Brooks, W.
S. Wolbach, R. S.
Smalley, Science 256, 545 (1994).
4. P. J. F. Harris, R. D. Vis, D. Heymann, Earth
Planet. Sci. Lett.
183, 355 (2000).
5. Y. G. Gin, et al., Science 289, 432 (2000).
6. The boundary layer (Bed 25) provided by S.
Bowring was from a
collecting trip in 1996 and is the same material
that preserved the
carbonate isotopic excursion reported in (5). Our
sample contained a
thin layer of carbon-rich material in the basal
portion of Bed 25 (15)
and is consistent with our finding of fullerene (a
pure carbon
molecule). In contrast, the samples provided to
Farley and Mukhopadyay
were from a different collecting trip (1999) and
apparently did not
contain the carbonaceous layer found in samples
collected in 1996 (see
discussion in text).
7. These values should have been reported as
upper-limit
concentrations in our paper (1), because the VG5400
mass spectrometer
has an abundance sensitivity of 108 for helium. A
significant fraction
of the 3He signal for nonboundary samples at Meishan
is from the
low-energy tail of the 4He (the MAP 215-50 mass
spectrometer used by
Caltech does not have this limitation).
8. Y. Kakuwa, Palaeogeogr. Palaeoclimatol.
Palaeoecol. 121, 35 (1996).
9. A. H. Knoll, et al., Science 273, 452 (1996).
10. S. Miono, et al., Nucl. Instrum. Methods Phys.
Res. B109, 612 (1996).
11. S. Miono et al., Lunar Planet Sci. XXIX (1998)
(CD-ROM).
12. K. Kaiho, et al., Geology 29, 815 (2001).
13. Y. Miura, et al., Adv. Space Res. 25, 285
(2000).
14. S, Miono, Y. Nakayama and K. Hanamoto, Nucl.
Instrum. Methods
Phys. Res. B150, 516 (1999).
15. S. Bowring, D.H. Erwin, personal communication.
20 July 2001; accepted 12 September 2001
Volume 293, Number 5539, Issue of 28 Sep 2001, p.
2343.
Copyright © 2001 by The American Association for
the Advancement of
Science.
===========
(9) ASTEROID TSUNAMI SIMULATION: NEW WAVE SUPERCOMPUTERS CATCH
BIG WAVES
>From Space Daily, 5 June 2002
http://www.spacedaily.com/news/earthquake-02a.html
Albuquerque - June 5, 2002
The new wave in computing - super-fast machines churning out
three-dimensional models viewable in high-tech, immersive
theaters - may
teach us more about the big waves that sometimes threaten people
who live
near the seashore.
Although earthquakes cause most of these giant waves, called
tsunamis,
researchers at the National Nuclear Security Administration's Los
Alamos
National Laboratory recently completed the largest and most
accurate
simulation of tsunamis caused by asteroids. They presented the
first data
from that model today to the American Astronomical Society
meeting in
Albuquerque,
The scientists aren't working on a sequel to the Hollywood
blockbusters Deep
Impact or Armageddon. They reason that since a large percentage
of the
world's population lives on islands, bays or coastlines, a better
model
could help predict how tsunamis behave, aiding emergency
responders.
Most tsunamis often result when earthquakes send huge landslides
tumbling
into bays or oceans. Recent studies of a 30-foot-high tsunami
that killed
more than 2,100 people on Papua New Guinea in July 1998 showed
the cause was
an underwater landslide more than 2,000 miles away. A landslide
in Lituya
Bay, Alaska, in July 1958 inundated the shore of Gilbert Inlet
nearly a
third of a mile above the high tide line, and its monster wave is
the
largest ever documented.
Computer scientists Galen Gisler and Bob Weaver from the Los
Alamos'
Thermonuclear Applications Group, and Michael Gittings of Science
Applications International Corp., created simulations of six
different
asteroid scenarios, varying the size and composition of a space
visitor
hitting a three-mile-deep patch of ocean at a speed of 45,000
miles an hour.
The Big Kahuna in their model was an iron asteroid one kilometer
in
diameter; they also looked at half-sized, or 500-meter, and
quarter-sized
variants, and at asteroids made of stone, roughly 40 percent less
dense than
iron.
"We found that the one-kilometer iron asteroid struck with
an impact equal
to about 1.5 trillion tons of TNT, and produced a jet of water
more than 12
miles high," Gisler said.
The team's effort builds on the pioneering research of Los
Alamos' Chuck
Mader and Dave Crawford of Sandia National Laboratories. More
accurate
models of tsunami behavior are now possible, thanks to recent
improvements
in high-performance computers and the codes that run on them
funded by the
NNSA's Advanced Simulation and Computing program.
"Although this is important science and has potential value
in predicting
and planning emergency response, it's an great way to test and
improve the
code," Gisler said. "We can do the problem better now
by simulating an
entire tsunami event from beginning to end and bringing more
computing power
to bear on some of the key variables."
The code, called SAGE for SAIC's Adaptive Grid Eulerian, was
developed by
Los Alamos and SAIC. A majority of large simulations come in one
of two
flavors: Lagrange, in which a grid or mesh of mathematical points
matches
with and follows molecules or other physical variables through
space; or
Eulerian, in which the mesh is fixed in space, thereby permitting
researchers to follow fluids as they move from point to point.
SAGE's power lies in its flexibility. Scientists can continuously
refine the
mesh and increase the level of detail the code provides about
specific
physical elements in the mesh. The new Los Alamos simulation uses
realistic
equations to represent the atmosphere, seawater and ocean crust.
To follow a tsunami from the point of splashdown to a city like
Honolulu or
Long Beach, Gisler and his colleagues needed to model in great
detail the
interactions between air and water and between water and the
surface of an
asteroid. Then they followed how the shock waves moved through
the ocean and
the seabed below and how water waves propagated through the
water.
"We looked in some detail at a couple of the key variables,
especially the
heights of tsunamis as a function of their distance from the
point of
impact; we modeled the heights of individual waves and studied
how densely
spaced they would be at various distances," Gisler
explained.
When the enormous simulation was done - more than a million hours
of
individual processor time, or three weeks on Los Alamos' Blue
Mountain
supercomputer and the ASCI White machine at Lawrence Livermore
National
Laboratory - the team found they had some good news and some bad
news for
coastal dwellers.
"The waves are nearly double the height predicted in the
earlier simulation,
that's the bad news, but they take about 25 percent longer to get
to you,
which could help more people get to higher ground if they had
some warning,"
Gisler said.
The model predicts that wave velocities for the largest asteroid
will be
roughly 380 miles an hour, while the older model calculated their
speed at
close to 500 miles an hour. However, the initial tsunami waves
are more than
half a mile high, abating to about two-thirds of that height 40
miles in all
directions from the point of impact.
The earlier model of asteroid-caused tsunamis actually was a
patchwork of
three different computer codes, Gisler said. The first code
simulated the
big splash and formation of the cavity, the second depicted how
the water
collapsed to create the tsunami and a final code followed the
tsunami wave
through the ocean.
"With the SAGE code, we were able to avoid a series of
potential mistakes
that happen when the model doesn't understand the conditions that
you're
passing on from each separate code," Gisler said.
In addition to learning more about how wave height and density
vary with
distance from the asteroid impact, the Los Alamos team also
improved the way
the computer model represents the strength of materials, which
can be
applied to other codes with industrial, defense and scientific
applications.
As the asteroid strikes the water, its overall density decreases
rapidly.
One challenge for the team was to model accurately how acoustic
waves
propagate through the asteroid as it vaporizes. Initially, that
problem
appeared insurmountable because both the earlier codes and SAGE
showed the
acoustic waves -moving at physically impossible speeds through
the highly
mixed materials. By adjusting how the cells in the mesh represent
those
rapidly changing materials, the team was able to model the
acoustic waves
accurately.
Gisler said the team produced both two-dimensional and
three-dimensional
versions of the SAGE tsunami code. The 3-D code required more
than 200
million separate cells and ran for three weeks on one-eighth of
ASCI White.
Clever code writing and the enormous computational power in the
3.1 teraOPS
Blue Mountain and 12.1 teraOPS ASCI White weren't the only
crucial factors
in building the model.
"It's not all about better and better resolution,"
Gisler said. "You must
have good visualization techniques, such as the three-dimensional
power
walls we use at Los Alamos, if you're going to make sense of the
data from
these huge calculations."
The modeling continues. Gisler, Weaver and Gittings next plan to
study in
three dimensions how an asteroid-induced tsunami will behave if
the space
rock strikes a glancing blow, 30 degrees from the horizontal,
instead of the
45- and 90-degree angles they've already calculated.
Los Alamos National Laboratory is operated by the University of
California
for the National Nuclear Security Administration of the
Department of Energy
and works in partnership with NNSA's Sandia and Lawrence
Livermore national
laboratories to support NNSA in its mission.
Los Alamos enhances global security by ensuring the safety and
reliability
of the U.S. nuclear weapons stockpile, developing technical
solutions to
reduce the threat of weapons of mass destruction and solving
problems
related to energy, environment, infrastructure, health and
national security
concerns.
Copyright 2002, Space Daily
==============
(10) THE INSPIRATION OF ASTRONOMICAL PHENOMENA -- FOURTH
CONFERENCE
>From Rolf Sinclair <rolf@SANTAFE.EDU>
THE INSPIRATION OF ASTRONOMICAL PHENOMENA -- FOURTH CONFERENCE
Magdalen College, Oxford (UK) August 3-9, 2003
SECOND ANNOUNCEMENT AND CALL FOR ABSTRACTS/PAPERS
This is the second announcement for the Fourth International
Conference on
The Inspiration of Astronomical Phenomena ("INSAP IV")
which is now
confirmed to take place in Oxford, England, 3-9 August 2003.
As at previous meetings (Castel Gandolfo, 1994; Malta, 1999;
Palermo, 2001),
the conference will explore humanity's fascination with
astronomical
phenomena as strong and often dominant elements in life and
culture. The
conference will provide a meeting place for artists and scholars
from a
variety of disciplines (including Archaeology and Anthropology,
Art and Art
History, Classics, History and Prehistory, the Physical and
Social Sciences,
Mythology and Folklore, Philosophy, and Religion) to present and
discuss
their studies on the influences of astronomical phenomena and
address topics
of common interest.
The fourth meeting will be held at Magdalen College, Oxford (UK),
starting
Sunday 3 August, 2003. There will be a wide range of guest and
keynote
speakers, with confirmed speakers so far including:
Professor Ronald Hutton, University of Bristol
Professor John North, University of Oxford
Opportunities will be provided for 30 minute presentations as
well as poster
presentations and the new application form is now linked within
the
"application process" section in the INSAP IV webpage:
http://ethel.as.arizona.edu/~white/insap/i4applyx.htm
During the meeting there will be receptions at the Ashmolean
Museum, the
Christ Church Picture Gallery, and the Museum of History of
Science. The
traditional banquet will be held at the Magdalen College dining
hall. A trip
is being planned to Stonehenge and Avebury.
Applications to attend and abstracts must be submitted by 1
December 2002 to
Professor Ray White (rwhite@as.Arizona.edu)
Mr Nick Campion (ncampion@caol.demon.co.uk)
Details of abstracts and proceedings of previous meetings are
described on
the website relating to each INSAP Conference, and will give an
idea of the
range of subjects presented at these meetings. A similar
publication is
planned for the fourth meeting. Further information on INSAP IV
and on the
earlier conferences, can be found on the following websites:
http://ethel.as.arizona.edu/~white/insap
(general information)
http://ethel.as.arizona.edu/~white/insap/insap4x.htm
(for INSAPIV)
http://ethel.as.arizona.edu/~white/insap/insap3.htm
and
http://www.astropa.unipa.it/INSAPIII/index.html
(for INSAPIII)
Attendance will be by invitation from among those applying. All
presentations and discussions will be in English. This Conference
is
sponsored by the Vatican Observatory and the Steward Observatory
For further information, contact the above or members of the
International
Executive or Local Organising Committees (contact details and
email
addresses as provided on the INSAPIV website).
June 3, 2002
Please circulate or post this announcement.
================
(11) CRATERS?
>From Giesinger Norbert <norbert.giesinger@siemens.com>
Dear Dr. Peiser,
looking on a NASA Satellite picture of the Balcan, I
immediately saw some
(vegetation enhanced) markings resembling parts of craters.
See the attaches. In the second, a big circular structure and a
small one in
the right lower corner. The pic is from
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=9270
Text:
The Transylvanian Basin in Romania stands out in brilliant green
in this
image from the Moderate-resolution Imaging Spectroradiometer
(MODIS) on May
3, 2002. Near the top of the image, the hilly, forested basin is
tucked in
between the Carpathian Mountains, running northwest-southeast,
and the
Transylvanian Alps, running west-east. To the right of the image
is the
Black Sea. The large patch of turquoise water in the Black Sea
</Newsroom/NewImages/Images/images.php3?img_id=9265> is a
large
phytoplankton bloom. At the bottom of the image, the Aegean Sea
and the Sea
of Marmara is ringed by Greece (left) and Turkey (right).
Greetings from Vienna
Norbert Giesinger
===========
(12) WHY IS MARS SO HARD?
>From James Oberg <joberg@houston.rr.com>
This conference outside of Washington, DC, in September will have
a panel on
'Why Is Mars So Hard?', with a gaggle of NASA officials, and me.
Look
forward to illumination from struck sparks!
http://klabs.org/richcontent/MAPLDCon02/panel/panel.htm
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