[meteorite-list] Latest from Gerta Keller - Chixilub didn't really do it...

From: cdtucson at cox.net <*cdtucson_at_meteoritecentral.com*> Date: Fri, 18 Nov 2011 13:52:07 -0500 Message-ID: <20111118135207.TEPUS.44839.imail_at_fed1rmwml207> · cdtucson_at_meteoritecentral.com

--
Cheers
---- Galactic Stone & Ironworks <meteoritemike at gmail.com> wrote: 
> Hi David and List,
> 
> Interesting theory.  I am a little confused at what this new research
> is trying to say.
> 
> Are they claiming that the volcanism from the Deccan Traps is largely
> responsible for the mass extinctions and that the coincidental
> meteorite impact aggravated the problem?
> 
> Or, are they claiming that a meteorite impact near the area of the
> Deccan Traps triggered the resulting volcanism?
> 
> It is not inconceivable to think that the latent potential of the
> Deccan Traps was unleashed by a catastrophic meteorite impact that
> punctured the crust and released the volcanism that caused the
> extinctions?  In effect, this would mean that the Deccan Traps would
> not have caused the extinctions on their own, because the volcanism
> would not have been "triggered" if the meteorite impact had not
> happened.
> 
> Considering the massive size and global cataclysmic effects caused by
> the Chicxulub event, it is hard to imagine that such an impact could
> not have caused the extinctions on it's own without any help from
> unrelated volcanism.  However, if the Deccan Traps were already
> pummeling life on Earth with it's toxic effects, then the subsequent
> Chicxulub event may have been the knock out punch that finished off
> the species that were already on the ropes from the Deccan volcanism.
> 
> Either way, the new research still admits that a meteorite impact
> played a role - even if it was secondary.
> 
> Best regards,
> 
> MikeG
> 
> -- 
> ---------------------------------------------------------------------------------
> Galactic Stone & Ironworks - Meteorites & Amber (Michael Gilmer)
> 
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> 
> 
> 
> On 11/18/11, David R. Vann <drvann at sas.upenn.edu> wrote:
> >
> > Not sure how much I agree with all this, but it sures seems the end
> > Cretaceous
> > would have been a bad time to be on planet Earth.
> >
> > One-Two Punch Caused Mass Extinction
> > November 18, 2011
> >
> > Princeton Univ. researchers found that massive, prolonged eruptions of the
> > Deccan Traps in India gradually eliminated species and resulted in the
> > Cretaceous-Tertiary mass extinction that killed the dinosaurs 65 million
> > years
> > ago. Marine sediment trapped between Deccan lava flows revealed that a
> > species
> > known as planktonic foraminifera-widely used to gauge the severity of
> > prehistoric disasters-succumbed to lava mega-flows and volcano-induced
> > environmental stress such as acid rain and drastic climate changes. As
> > conditions on Earth worsened, large, variedspecies (left) were eliminated.
> > The
> > no more than seven or eight smaller species (right) that remained dwarfed
> > further. Image: Gerta Keller
> > A cosmic one-two punch of colossal volcanic eruptions and meteorite strikes
> > likely caused the mass-extinction event at the end of the Cretaceous period
> > that
> > is famous for killing the dinosaurs 65 million years ago, according to two
> > Princeton Univ. reports that reject the prevailing theory that the
> > extinction
> > was caused by a single large meteorite.
> >
> > Princeton-led researchers found that a trail of dead plankton spanning half
> > a
> > million years provides a timeline that links the mass extinction to
> > large-scale
> > eruptions of the Deccan Traps, a primeval volcanic range in western India
> > that
> > was once three-times larger than France. A second Princeton-based group
> > uncovered traces of a meteorite close to the Deccan Traps that may have been
> > one
> > of a series to strike the Earth around the time of the mass extinction,
> > possibly
> > wiping out the few species that remained after thousands of years of
> > volcanic
> > activity.
> >
> > Researchers led by Princeton professor of Geosciences Gerta Keller report
> > this
> > month in the Journal of the Geological Society of India that marine
> > sediments
> > from Deccan lava flows show that the population of a plankton species widely
> > used to gauge the fallout of prehistoric catastrophes plummeted nearly 100
> > percent in the thousands of years leading up to the mass extinction. This
> > eradication occurred in sync with the largest eruption phase of the Deccan
> > Traps-the second of three-when the volcanoes pumped the atmosphere full of
> > climate-altering carbon dioxide and sulfur dioxide, the researchers report.
> > The
> > less severe third phase of Deccan activity kept the Earth nearly
> > uninhabitable
> > for the next 500,000 years, the researchers report. A substantially weaker
> > first
> > phase occurred roughly 2.5 million years before the second-phase eruptions.
> >
> > Another group based in Keller's lab found evidence in Indian sediment of a
> > meteorite strike from the time of the mass extinction that would have been
> > sufficient to finish off the few but weakened species that survived the
> > Deccan
> > eruptions, according to a report in the journal Earth and Planetary Science
> > Letters (EPSL). This same sediment-located in Meghalaya, India, more than
> > 600
> > miles east of the Deccan Traps-portrayed the Earth during this period as a
> > harsh
> > environment of acid rain and erratic global temperatures.
> >
> > Taken together, Keller says, the Princeton findings could finally put to
> > rest
> > the theory that the mass-extinction event-known as the Cretaceous-Tertiary,
> > or
> > KT, for the periods it straddles-was triggered solely by a large meteorite
> > impact near Chicxulub in present-day Mexico. That impact -which occurred
> > around
> > the time of the second-phase Deccan eruptions-is thought to have been 2
> > million
> > times more powerful than a hydrogen bomb and generated an enormous dust
> > cloud
> > and gases that radically altered the climate. Keller has long held that the
> > Chicxulub impact was not catastrophic enough to cause the KT mass
> > extinction-the
> > newest work from her lab, however, shows that the largest Deccan eruptions
> > were.
> >
> >
> > "Our work in Meghalaya and the Deccan Traps provides the first one-to-one
> > correlation between the mass extinction and Deccan volcanism," says Keller,
> > who
> > is lead author of the Geological Society paper and second author of the EPSL
> > paper after lead author Brian Gertsch, who earned his Ph.D. from Princeton.
> > Gertsch is now a postdoctoral researcher at the Massachusetts Institute of
> > Technology.
> >
> > "We demonstrate a clear cause-and-effect relationship that these massive
> > volcanic eruptions were far more destructive than previously thought and
> > could
> > have caused the KT mass extinction even without the addition of large
> > meteorite
> > impacts," Keller says. "But given the environmental instability caused by
> > the
> > massive Deccan eruptions, an impact could easily have killed off the few
> > survivor species at the end of the Cretaceous. It would have been a double
> > whammy."
> >
> > Vincent Courtillot, a geophysicist and professor at Paris Univ. Diderot,
> > says
> > that the Princeton papers are based on a closer examination of Deccan
> > volcanism
> > and its aftermath than has been conducted previously. As such, he says, the
> > researchers' "impressive analysis" confirms the timing of the Deccan
> > eruptions
> > and environmental fallout reported in recent years by various research
> > teams,
> > including his own.
> >
> > Courtillot, who is familiar with the Princeton work but had no role in it,
> > led
> > the team that reported in the Journal of Geophysical Research in 2009 that
> > Deccan volcanism occurred in three phases, the second and largest of which
> > coincides with the Cretaceous-Tertiary mass extinction; the Keller-led study
> > published in the Journal of the Geological Society of India confirms the
> > second
> > and third phases, he says.
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> >
> > "The significance of this recent work is that the analysis was conducted in
> > important sections near the volcanic action, and not thousands of kilometers
> > away as had been the case previously," Courtillot says. "They provide
> > support
> > for the idea that carbon and sulfur dioxide emissions were the principal
> > agents
> > of environmental change and stress, and conclude that the characteristics of
> > the
> > second-phase eruptions were such that it could alone have caused the mass
> > extinction."
> >
> > In addition, Courtillot says, the approach the teams used could prove
> > valuable
> > to understanding the part volcanoes played in other extinction events in
> > Earth's
> > history. "Exceptional, massive volcanism, I am now quite sure, is the
> > general
> > cause of mass extinctions," he says. "But in order to be considered as
> > proven
> > and quantitatively explained, we need the kind of extensive, detailed work
> > described by these teams to be conducted for all other extinctions."
> >
> > The case for Deccan over the Chicxulub impact as the cause of the KT
> > extinction
> >
> > Keller is prominent among scientists who reject the Chicxulub impact's role
> > in
> > the end-Cretaceous mass extinction. She is well known for leading a team of
> > researchers who announced in 2003 that a sediment core from the Chicxulub
> > crater
> > revealed that the impact predated the mass-extinction event by about 300,000
> > years.
> >
> > Keller and her co-authors published their findings in the journal
> > Proceedings of
> > the National Academy of Sciences in 2004 and suggested that the Chicxulub
> > meteorite was instead one of several meteorite strikes that occurred in the
> > several hundred thousand years leading up to the mass-extinction event. They
> > concluded that while destructive, the Chicxulub impact was not powerful
> > enough
> > to have caused widespread annihilation. Keller and her collaborators have
> > since
> > supported these findings with additional evidence from Texas and
> > northeastern
> > Mexico published in EPSL in 2007 and the Journal of the Geological Society
> > of
> > London in 2009, respectively.
> >
> > Keller has joined other scientists in focusing her research on the
> > 30-year-old
> > idea first championed by Virginia Tech geologist Dewey McLean that Deccan
> > volcanism was the root of the Cretaceous mass extinction. Until recently,
> > the
> > theory was in question because the eruptions were thought to have been
> > stretched
> > out over a period of more than 1 million years, leaving plenty of time for
> > the
> > Earth to recover between eruptions, Keller says.
> >
> > Improved dating technology, however, allowed scientists-particularly the
> > team
> > led by Courtillot-to narrow the time of the largest eruptions to a few
> > hundred
> > thousand years at the end of the Cretaceous. Known as Deccan phase-2, this
> > period accounted for 80 percent of the total volcanism. The first and
> > weakest
> > phase of activity occurred about 67.5 million years ago; the third and final
> > eruption phase began about 300,000 years after the KT mass extinction.
> >
> > In 2008, Keller and her team reported in EPSL the first direct link that the
> > KT
> > extinction coincided with the end of the second phase of Deccan eruptions.
> > She
> > explained that marine sediments preserved between lava flows from the
> > second-
> > and third-phase eruptions contained evidence of the KT boundary, a thin,
> > worldwide geological layer that marks the mass-extinction event.
> >
> > Deccan volcanism behind the mass extinction, so say the plankton
> >
> > The work published Nov. 1 by the Geological Society of India builds on
> > Keller's
> > 2008 paper in EPSL. She and her co-authors examined cores from Deccan lava
> > flows
> > near Rajahmundry in the Krishna-Godavari Basin, the remnant of an ancient
> > sea on
> > the Bay of Bengal coast, and found that lava flows from the second and third
> > Deccan phases are separated by marine sediments.
> >
> > Keller worked with scientists with India's government-operated Oil and
> > Natural
> > Gas Corporation, which owns the sediment cores. Also included is Thierry
> > Adatte,
> > a geologist with the Univ. of Lausanne in Switzerland, who is Keller's
> > long-time
> > collaborator and a co-author on the papers challenging the time of the
> > Chicxulub
> > impact, as well as previous papers on Deccan volcanism.
> >
> > The team examined the basin's sediment layers to determine the size and
> > number
> > of a species known as planktonic foraminifera that remained following each
> > eruption phase. These plankton are single-celled micro-organisms ranging in
> > size
> > from the point of a needle to a pinhead that are highly sensitive to changes
> > in
> > oxygen, salinity, temperature and nutrients, Keller says. Their sensitivity
> > to
> > environmental changes and their near extinction at the end of the Cretaceous
> > makes the species key to determining the timespan, pace and severity of the
> > mass
> > extinction.
> >
> > After studying microplankton remains in sediment from below, between and
> > above
> > the second-phase lava flows, the researchers observed that the number of
> > living
> > species dropped 50 percent at the onset of eruptions. The species count
> > plunged
> > by another 50 percent after the first of what would be four lava mega-flows.
> > No
> > more than seven to eight of the species that were most tolerant to
> > environmental
> > changes survived after the first mega-flow, and no recovery occurred between
> > subsequent mega-flows. By the end of the fourth mega-flow the mass
> > extinction
> > was complete, the researchers wrote.
> >
> > The vast amounts of carbon dioxide and sulfur dioxide poured into the
> > atmosphere
> > by the end of the second volcanic phase-estimated to be 30-times more than
> > the
> > levels produced by the Chicxulub impact-resulted in, among other crises,
> > heavy
> > acid rain, acidic oceans and global temperatures that swung between
> > scorching
> > and frigid, the researchers report. The third eruption phase prolonged these
> > conditions.
> >
> > Thus, the number of species evolving remained low, and existing species
> > dwarfed
> > during the 500,000-year period after the mass extinction, although no
> > significant extinctions occurred again, Keller and her co-authors found.
> > New,
> > larger marine species did not appear until after the third phase when Deccan
> > eruptions went dormant, suggesting that life began to recover as the
> > atmosphere
> > became less poisonous.
> >
> > "In my work, I had always observed evidence of marked changes in species
> > abundance with gradually higher levels of stress and extinction during the
> > last
> > several hundred thousand years, rather than one single instantaneous
> > annihilation," Keller says. "For lack of better evidence, scientists had
> > interpreted this steady decline as the result of climate and sea-level
> > changes."
> >
> >
> > Evidence that a large meteorite helped finish the job
> >
> > For the paper published in EPSL, Keller and her co-authors provide a
> > supporting
> > and more nuanced depiction of conditions during the Deccan period. They
> > examined
> > sediments from an ancient shallow sea in Meghalaya where rock layers are
> > known
> > to contain among the clearest fossil records of the Cretaceous-Tertiary mass
> > extinction, Keller says.
> >
> > Analysis of the Meghalaya sediment revealed an inhospitable planet rife with
> > high humidity, severe storms and massive blooms of the plankton species
> > Guembelitria cretacea, a disaster opportunist that flourished in devastated
> > environments when few other species survived.
> >
> > At the same time, the team detected large amounts of iridium, an element
> > typically associated with meteorite impacts, Keller says. Iridium is rare on
> > Earth yet is found in high concentrations in the KT boundary, a phenomenon
> > known
> > as the iridium anomaly. Remnants of iridium at the KT boundary in Meghalaya
> > coincide with the global KT boundary iridium anomaly, she says.
> >
> > The new evidence of a meteorite strike at Meghalaya that coincides with the
> > KT
> > mass extinction supports the theory Keller proffered in 2003 that multiple
> > meteorites struck the Earth around the time of the Deccan eruptions, adding
> > to
> > the volcano-fueled misery of the mass-extinction era.
> >
> > "Our data suggest that the mass extinction of the dinosaurs and other
> > species
> > was caused by the harsh conditions resulting from massive Deccan eruptions
> > and
> > the coincidence of multiple meteorites," Keller says. "In light of this new
> > evidence, the single-impact story seems more like an article of faith at
> > this
> > point."
> >
> > The study published in the Journal of the Geological Society of India about
> > the
> > Deccan eruption and the meteorite research published in EPSL were both
> > supported
> > by grants from the National Science Foundation.
> >
> > Source: Princeton Univ.
> >
> >
> > David R. Vann, Ph.D.
> > Department of Earth and Environmental Science
> > THE UNIVERSITY of PENNSYLVANIA
> > 240 S. 33rd St.
> > Philadelphia, PA 19104-6316
> > drvann at sas.upenn.edu
> > office: 215-898-4906
> > FAX: 215-898-0964
> >
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