[meteorite-list] Meteor Impact Theory Takes a Hit

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Jan 20 22:22:55 2005
Message-ID: <41F072D3.8FCF2F76_at_bhil.com>

Hi,

    All these "the asteroid didn't do it" papers are a good sign. I remember
the more than 10 years it took to swing opinion on the Cretacious-ending
event. We had all the same "but, but, but" proposals. We were told that the
number of species of dinosaurs had been declining for millions of years ---
they were going to die off anyway and that big rock was just a coincidence!
    Not mentioned in this press release is another study of the Permian
extinction that came out this week, claiming that oceanic bacteria poisoned
the Earth. This is reminiscent of the prominent dinosaur scholar who
insisted all the varieties of Cretaceous life that died off were killed by
diseases from allied and migratory species. They just got sick and died and
that big rock was just a coincidence!
    Pitiful. The theory that a species can be extinguished by diseases from
its own species has been around for two centuries despite the fact that no
one has ever found any evidence of any species extincted by disease, ever.
But I must admit I admire the "bacteria poisoned the earth" theory: a new
high in whacky.
    And vulcanism as a world-ending event has been a favorite catastrophe
since the latter XVIIIth century and is always the first and favorite "not a
rock" theory. The only old medieval crap still not popular is The Flood!
    And what could be more stylishly a la mode than a theory that global
warming caused The Great Dying? Obviously, this massive extinction was
caused by the inability of amphibians and reptiles to draft a Permian Kyoto
Treaty!
    And why do only we get the "cute" headline style? Impact Theory Takes A
Hit? Why not, Disease Theory Gets Sick, or Volcano Theory Blows Up, or Global
Warming Theory Cools Down?
    My point being: bring on the silliness. We have to get through it, so
the sooner the better. And yes, we have to prove an impact. But I remember
the long gap between the iridium excess and the discovery of Chixilub during
which there was a "yah yah you have to prove it" paper or review every few
months for years and years in response to each new piece of evidence that was
not a crater, the propose of which was not reiterate the obvious 500 times
but to say in effect "I will not believe in your rock until you show it to
me."
    As for the slow progression toward what comes to recognized as a
fundamental reality, remember: paradigms, or "systems of the worlds" as
Gallileo called them, do not die; only the individuals who support them.
    We may naively believe that scientific truth is the same everywhere, but
even that is not true. For example, British geologists, and the Australian
geologists who were their students, were still resolute about asserting the
volcanic origin of the craters of the Moon into the 1980's! (Meanwhile,
British astronomers are standing there shaking their heads in dismay.) One
of my treasured possessions is an Australian geology text published in 1978
that is absolutely vitriolic in asserting for three chapters that there is
"no evidence of any impact on the Moon." (The author also denied impact
craters on Earth, too.) I love it!
    Anyway, the old farts die or retire and everyone politely forgets their
imbecilities. That's how opinions "change." The amazing thing is how long
it takes knowledge to percolate through the dried clay of human thought.
It's been four centuries since we figured out that comets were in space not
the atmosphere, four centuries since we saw the craters on the Moon, two
centuries since we admitted that rocks can fall from the sky, two centuries
since we discovered the first asteroid, not to mention everything learned in
the last 50 years, and still it's "Tut, tut, big rock? I don't think so."
    Pitiful.


Sterling K. Webb
-------------------------------------------------------
Ron Baalke wrote:

> http://www.wired.com/news/technology/0,1282,66345,00.html?tw=wn_tophead_4
>
> Meteor Impact Theory Takes a Hit
> By Amit Asaravala
> Wired News
> January 20, 2005
>
> The catastrophe that killed off the majority of life on Earth 250
> million years ago was not a meteorite impact, but a gradual rise in
> global temperatures, according to a new study published Thursday on the
> website of the journal Science.
>
> The study is the second in two months to question the validity of the
> meteorite impact theory, which suggests that a giant asteroid or comet
> struck the Earth with such force that it led to a massive, global
> extinction that scientists call the "Great Dying."
>
> The impact would have been similar to the one that is widely believed to
> have led to the extinction of the dinosaurs 65 million years ago. But to
> date, evidence for the dinosaur's demise has far exceeded that for the
> Great Dying.
>
> "We all assumed in the scientific community that if one extinction could
> be caused by an impact, they all could," said Peter Ward, a University
> of Washington paleontologist and lead author of the new study. "I went
> (to South Africa) specifically to prove that this was caused by an
> impact and walked out of there thinking that, no, it wasn't."
>
> Ward and his fellow researchers traveled to the Karoo Basin in South
> Africa to examine fossils that have been traced back to the time of the
> Great Dying, also known as the end-Permian period. Rather than finding
> that a great number of animals and plants had all died at once, however,
> the team detected signs of a gradual extinction over nearly 10 million
> years. Then, a second extinction seems to have started and lasted
> approximately 5 million years.
>
> Such patterns suggest that long-term environmental changes, like global
> warming and falling oxygen levels, are more to blame than a meteor
> impact, said Ward. Continuous volcanic eruptions during the end-Permian
> period could have contributed to these changes by triggering the release
> of methane that had previously been frozen at the bottom of the ocean,
> he suggested.
>
> Ward added that the team did not find, in the sediment that it examined,
> the sorts of minerals that are normally associated with meteorite
> impacts. Those minerals include iridium, which hitches a ride to Earth
> on asteroids, and "shocked" quartz, which takes on an altered appearance
> after a massive impact.
>
> The findings -- or lack thereof -- contradict a controversial study
> published in June 2004 by Science. In that study,
> University of California at
> Santa Barbara geologist Luann Becker and several other scientists
> claimed to have discovered evidence of a giant impact crater off the
> coast of Australia. The crater could be dated back to the beginning of
> the Great Dying, they wrote in the study, making it the likely cause of
> the mass extinction.
>
> However, a number of geologists have since questioned the evidence.
>
> "They've been very broadly criticized," said Paul Renne, director of the
> Berkeley Geochronology Center. "Many of their claims are completely
> unsupportable."
>
> The impact theory received another major blow in December when a team
> led by geologist Christian Koeberl from the University of Vienna
> published a paper in the journal Geology showing that samples of
> end-Permian rock in Western Europe did not contain iridium and shocked
> quartz.
>
> University of Rochester geochemist Robert Poreda, who co-authored the
> June impact paper with Becker, defended his team's study Wednesday and
> said that he still supported the impact theory.
>
> "A lot of things can explain why there was no evidence of shocked
> quartz," he said. "For one, there's not a complete section (of sediment)
> to analyze at Karoo."
>
> In addition, an impact off the coast of Australia would not have struck
> the appropriate rocks that would lead to the creation of mass quantities
> of shocked quartz, he said. Plus, an impact by a comet -- not an
> asteroid -- would probably not have carried iridium with it, he added.
>
> Berkeley's Renne, who was not involved in any of the aforementioned
> studies, agreed that Poreda's arguments are valid. However, he noted
> that he and many of his colleagues were beginning to have less and less
> faith in the impact theory. Indeed, Renne's own research supports the
> idea that the extinction occurred gradually, he said.
>
> "We've found that the atmosphere was changing, in terms of oxygen levels
> and in carbon and so on -- all told, these things were probably going on
> over a million years," he said. "And we're beginning to think that the
> main pulse of extinction occurred over 100,000 years, which is pretty
> fast in geologic time, but it's not an instant."
>
> To resolve the argument, scientists are now turning their attention to
> fullerenes, tiny balls of carbon that can lock up gases inside. If
> fullerenes taken from sediment dated back to the beginning of the Great
> Dying are found to contain gases more commonly found in space than on
> Earth, the chances are good that a large meteorite struck the planet
> around the same time.
>
> But even this technique has its problems, warned Renne.
>
> "A lot of things have to be done to establish a link between the gases
> in the fullerenes and an impact," he said. "The timing (of any detected
> impact) has to be perfect, and it has to be shown that this is an
> anomalous concentration of gas."
>
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Received on Thu 20 Jan 2005 10:11:15 PM PST