[meteorite-list] Volcanic Gases, Not Meteors, May Have Caused Mass Extinctions

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu Mar 16 18:08:25 2006
Message-ID: <005d01c6488e$90c1be50$0859e146_at_ATARIENGINE>

Hi,

    More information on the eleven flood basalt events that
have happened in the last 250,000,000 years can be found at:
<http://www.geolsoc.org.uk/template.cfm?name=fbasalts>
    The fact that there are only eleven such events in that
length of time indicates that these events are not a normal,
i.e., gradual and on-going geological process, but may have
a specific incidental cause (like an impact?).
    One explanation of how a major impact could cause a flood
basalt event is by decompression melting:
<http://www.mantleplumes.org/Impacts.html>
    Decompression melting is easy to understand; just try
suddenly removing the lid from a working pressure cooker!
(Don't really try this. You could be injured. My lawyer made
me write this parenthesis.)
    However, it's a little hard to support the idea that flood
basalts occur at the point of impact when you look at the
"coincidental" timing of the Chicxulub impact and the Deccan
Traps, unless you believe there were two impacts. And, indeed,
the two impact scenario has been proposed. (If you're going to
argue for decades, it's good to have lots of things to argue
about!)
    I have always favored the notion that the Traps occur at
the point on the globe directly opposite the point of impact,
by the focusing of shock waves at the "antipodes." The solar
system has examples of this phenomenon, like the "chaotic
terrain" on Mercury opposite the great Caloris Basin. Even
our little Moon shows some fracture features opposite the
Imbrium Basin. And the case has been made for some
features on Mars.
    Googling up a storm while the List was down, I found most
geologists utterly contemptuous of this idea. Naturally, this made
me like it better. I found that their major objection to this is that
the location of the Traps is NOT precisely "antipodal" to the
impact sites. There is a heralded claim by a prominent geologist
that the offset between the Chicxulub impact and the Deccan
Traps was 30 degrees or even 50 degrees.
    So, I tried to find what their LatLong was 65 million years
ago, only to find that every reconstructor of past continental
drift comes up with a slightly different answer, varying from
a perfect "antipodal" match to about 50 degrees off. Hmm.
    Next, it was off to Seismology to study the focusing of
shock waves which of course is, in a mild way, what Seismology
is all about. After a certain amount of puzzling over diagrams
showing perfect "antipodal" focus, it dawned on me. In all cases,
Seismology assumes all forces to be "normal" (orthogonal) to
the surface of the Earth. They are, in an earthquake, but...
    This corresponds to an impact event only when the Big Rock
comes straight down from the zenith, a 90 degree impact. But, as
we know, this is an unlikely scenario for an impact.
<http://www.osti.gov/bridge/servlets/purl/10197028-5vKwmj/webviewable/10197028.pdf>
    Searching around to see what would happen if you struck
the Earth at an angle, like an impactor almost certainly would,
I discovered that -- yes, oblique impact shifts the direction of
the shock waves and the location of the "antipodal" focus.*
    This displacement of the primary focus of the shock waves
is almost as great as the angle of incidence, because they
are orthogonal -- to the impactor, not the Earth. So, "antipodal"
can be anywhere from less than 135 degrees up to 180 degrees
from the point of impact. This shifts the meaning of "antipodal"
considerably.
    Still, geologists seem to be terribly annoyed by the suggestion
that impacts could have seismic or volcanic effects. In my simple-
minded way, I look at it like this. The Earth is a ball of rock. (OK,
it has a delicious molten center, but mostly it's a ball of rock.) Rock
is defined as a crystal. That's what rocks are: crystals, maybe not
all gemmy, but crystals nevertheless. Take a hammer and hit a
crystal, very lightly at first but getting more energetic. At some
point, effects will commence. What happens? Well, cracks,
for a start. Forces in the crust (and mantle) are in equilibrium,
a meta-stable condition. How much does it take to disturb
an equilibrium of contained and constrained forces? Only a
fraction of the total forces in the equilibrium.
    If you like really whacky geologic notions, try Googling
"Verneshot"!
    The triggering of catastrophic vulcanism also goes a long
way to answering the question, "Exactly HOW did this asteroid
kill the dinosaurs?" It effectively sucks up all of the vulcanism
effects into the list of things that would be caused by the
impact. That full list of global nasties ought to be enough
to kill those dino guys. You hear so many that-couldn't-kill-
ALL-the-dinosaurs objections that you half expect to bump
into a raptor in the woods... All I know is I haven't seen
too many of them (outside of their wonderful movies) lately...


Sterling K. Webb
-------------------------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Monday, March 13, 2006 5:02 PM
Subject: [meteorite-list] Volcanic Gases, Not Meteors,May Have Caused Mass
Extinctions


>
> http://www.ens-newswire.com/ens/mar2006/2006-03-13-05.asp
>
> Volcanic Gases, Not Meteors, May Have Caused Mass Extinctions
> Environment News Service
> March 13, 2006
>
> LEICESTER, UK, March 13, 2006 (ENS) - Earth's history has been
> punctuated by mass extinctions that have rapidly wiped out nearly all
> life forms on the planet. To determine what caused these events, British
> geologists are challenging the currently held theory that meteorite
> impacts are to blame for wiping out the dinosaurs 65 million years ago
> and other mass extinctions.
>
> Professor Andy Saunders and Dr. Marc Reichow are testing the theory that
> gases released by volcanic activity led to a prolonged volcanic winter
> brought on by sulphur-rich aerosols, followed by a period of warming
> induced by carbon dioxide in the atmosphere.
>
> Flood basalt eruptions correspond with all main mass extinctions, says
> Saunders, within error of the techniques used to determine the age of
> the volcanism. Flood basalt eruptions are vast outpourings of lava that
> covered large areas of the Earth's surface, creating what geologists
> call flood basalt provinces.
>
> Saunder says, these flood basalt events may have released enough
> greenhouse gases - sulfur dioxide (SO2) and carbon dioxide (CO2) - to
> "dramatically change the climate."
>
> The largest flood basalt provinces on Earth, known as traps, coincide
> with the largest extinctions. The Siberian Traps correspond with the end
> of the Permian era some 251 million years ago when around 95 percent of
> all living species died out. The Deccan Traps in India correspond with
> the end of the Cretaceous era, some 65 million years ago when the
> dinosaurs disappeared, leaving only fossils.
>
> Saunders and Reichow at Leicester, in collaboration with Anthony Cohen,
> Steve Self, and Mike Widdowson at the Open University, have recently
> been awarded a Natural Environment Research Council grant to study the
> Siberian Traps and their environmental impact.
>
> The Siberian Traps are the largest known continental flood basalt
> province. Erupted about 250 million years ago at high latitude in the
> northern hemisphere. A scientific debate is underway concerning the
> origin of these provinces and their environmental impact that this
> research team hopes to clarify.
>
> Using radiometric dating techniques, they hope to constrain the age and,
> combined with geochemical analysis, the extent, of the Siberian Traps.
>
> Measuring how much gas was released during these eruptions 250 million
> years ago is "a considerable challenge," Saunders says.
>
> The researchers will study microscopic inclusions trapped in minerals of
> the Siberian Traps rocks to estimate the original gas contents. Using
> these data they hope to be able to assess the amount of SO2 and CO2
> released into the atmosphere 250 million years ago, and whether or not
> this caused climatic havoc, wiping out nearly all life on Earth.
>
> By studying the composition of sedimentary rocks laid down at the time
> of the mass extinction, they also hope to detect changes to seawater
> chemistry that resulted from major changes in climate.
>
>>From these data Professor Saunders and his team hope to link the
> volcanism to the extinction event. "If we can show, for example, that
> the full extent of the Siberian Traps was erupted at the same time, we
> can be confident that their environmental effects were powerful," said
> Saunders. "Understanding the actual kill mechanism is the next stage."
>
> The idea that meteorite impacts caused mass extinctions has been in
> fashion over the last 25 years, since Louis Alverez's research team in
> Berkeley, California published their work about an extraterrestrial
> iridium anomaly found in 65 million year old layers at the
> Cretaceous-Tertiary boundary.
>
> This anomaly only could be explained by an extraterrestrial source, a
> large meteorite, hitting the Earth and ultimately wiping out the
> dinosaurs and many other species, according to Alverez.
>
> Professor Saunders observed, "Impacts are suitably apocalyptic. They are
> the stuff of Hollywood. It seems that every kid's dinosaur book ends
> with a bang. But are they the real killers and are they solely
> responsible for every mass extinction on Earth?"
>
> There is scant evidence of impacts at the time of other major
> extinctions such as at the end of the Permian, 251 million years ago,
> and at the end of the Triassic, 200 million years ago. Saunders says the
> evidence that has been found does not seem large enough to have
> triggered an extinction at these times.
>
> Dr. Michael Benton, a professor of paleontology at Bristol University,
> is also studying the extinctions of 251 million years ago. "Over the
> past decade or so, new discoveries in the field and important progress
> in dating techniques have given us a more precise picture of this
> period," he wrote in April 2005.
>
> The suddenness and the scale of the event first suggested a collision
> with an asteroid or other meteor. Recent paleontological data suggest a
> different cause, Benton wrote in "RTD Info," a magazine on European
> research.
>
> Volcanic eruptions over 600, 000 years shook the only continent existing
> 251 million years ago, Pangaea. Huge eruptions occurred in what is now
> Siberia, spreading basaltic lava onto the Earth's surface across an area
> equivalent to the size of Europe to a depth of between 400 and 3,000
> meters - the Siberian Traps. Recent dating techniques place these
> eruptions at the end of the Permian era, Benton and Saunders' team both
> say.
>
> "Volcanism, and the colossal CO2 emissions that accompany it, are today
> seen by many scientists as the element that triggered the array of
> factors at the origin of this brutal crisis," Benton wrote.
>
> As far back as 1991, two American scientists suggested that the volcanic
> activity in Siberia was linked with the end-Permian extinctions.
>
> The work by Paul Renne of the Institute of Human Origins in Berkeley,
> California, and Asish Basu of the University of Rochester indicates that
> the volcanic activity occurred very rapidly.
>
> "This eruption occurred over an extremely short period of time,
> geologically speaking," said Renne in 1991. "We believe we've nailed the
> date down fairly precisely. It's even conceivable that it occurred over
> an interval as short as 200,000 years."
>
> There are other suggestions that atmospheric hydrogen sulfide and carbon
> dioxide led to the mass extinctions.
>
> In February 2005, Pennsylvania State geoscientist Dr. Lee Kump, studying
> bacteria in deep sea sediments, said the volcanic eruptions in Siberia
> 250 million years ago in the end-Permian period, may have started a
> cascade of events leading to high hydrogen sulfide levels in the oceans
> and atmosphere and precipitating the largest mass extinction in Earth's
> history.
>
> "The recent dating of the Siberian trap volcanoes to be contemporaneous
> with the end-Permian extinction suggests that they were the trigger for
> the environmental events that caused the extinctions," wrote Kump in
> 2005. "But the warming caused by these volcanoes through carbon dioxide
> emissions would not be large enough to cause mass extinctions by itself."
>
> As the levels of atmospheric oxygen fell and the levels of hydrogen
> sulfide and carbon dioxide rose, the upper levels of the oceans could
> have become rich in hydrogen sulfide. Kump says this would kill most the
> oceanic plants and animals and the hydrogen sulfide dispersing in the
> atmosphere would kill most terrestrial life.
>
> "A hydrogen sulfide atmosphere fits the extinction better than one
> enriched in carbon dioxide," says Kump. "Carbon dioxide would have a
> profound effect on marine life, but terrestrial plants thrive on carbon
> dioxide, yet they are included in the extinction."
>
> Another piece in the puzzle surrounding the end-Permian extinction is
> that hydrogen sulfide gas destroys the ozone layer. Recently, Dr. Henk
> Visscher of Utrecht University and his colleagues suggested that there
> are fossil spores from the end-Permian that show deformities that
> researchers suspect were caused by ultraviolet light.
>
> "These deformities fit the idea that the ozone layer was damaged,
> letting in more ultraviolet," says Kump.
>
> Once this process is underway, methane produced in the ample swamps of
> this time period has little in the atmosphere to destroy it. The
> atmosphere becomes one of hydrogen sulfide, methane and ultraviolet
> radiation.
>
> More about the research on Siberian Traps is online at:
>
> http://www.le.ac.uk/gl/ads/SiberianTraps/Index.html
>
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Received on Wed 15 Mar 2006 07:14:17 PM PST