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

From: Galactic Stone & Ironworks <*meteoritemike_at_meteoritecentral.com*> Date: Fri, 18 Nov 2011 12:08:12 -0500 Message-ID: <CAKBPJW8SyTj08fNF3VMRRo_cFrU8nXwUsnRNzZkGxQ5fRRKAzg_at_mail.gmail.com> · meteoritemike_at_meteoritecentral.com

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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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