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Re: causes of K-T ferns



 
----- Original Message -----
Sent: Wednesday, May 23, 2001 3:01 AM
Subject: causes of K-T ferns

     David Marjanovic mentioned a fern spore spike in New Zealand, which,
together with iridium etc., is putative evidence of the global effects of a
K-T asteroid spike.
      In fact, fern blooms can result from a variety of causes.  They cover
areas disturbed by volcanic eruptions.  Volcanism associated with the
Laramide Revolution occurred worldwide around K-T time.  By burning away the
usual plant cover, lavas provide opportunities for the proliferation of
resilient ferns.
You do know that the fern spike-containing sediments are on top of the K-T clay, not on top of lava flows?
I don't know all places where a post-K-T fern spike has been found, there may be more than just Montana and NZ.
Wolbach noted evidence of carbon concentration, or fire, in
the New Zealand K-T layer.  Inasmuch as New Zealand is far from Chicxulub
(even if it did occur 65 Ma.)  Volcanism may provide a better explanation for
local fires and subsequent fern blooms (but not dinosaur extinction,
directly, considering the benign nature of Deccan eruptions.)
The Chicxulub impact was a global event, in terms of its consequences. Deccan-derived lava, however, covers a large part of India -- not of the world.
      Of course, volcanism occurred in America too, and may explain local
ferns, iridium, etc.
I don't know how local the fern spike is in America. However, it doesn't occur on top of lava. And, for the 12876398th time, volcanos are TOTALLY INCAPABLE of producing iridium and osmium with EXTRATERRESTRIAL isotope ratios, shocked quartz, glass spherules derived from ocean floor, and so on. Even if the crater were still unknown, the K-T boundary layer alone would be proof of an impact.
Recent research, however, suggests another alternative
to an impact as a cause of fern proliferation: overgrazing.
Overgrazing at the time of an impact? What a coincidence.
      An expanded deer population has so stressed the flora that edible, or
preferred, vegetation has been replaced by ferns over wide areas.  Entire
forests have been seriously affected, not only by constant eating of
seedlings, but by the tendency of ferns to smother tree seeds.  Could this
have had a parallel around K-T time?
No, because such deer populations expand because of the absence of predators. This was obviously not the case at the K-T.
      Given the opportunity, Tyrannosaurus may have extirpated unprepared
foreign prey, but it probably could not have wiped out the highly "escalated"
defenders of America such as Triceratops.
Probably, you say. You try to build a hypothesis on a speculation. Sorry to say that -- this is AFAIK considered pseudoscience.
Hey! Why didn't Triceratops spread around the worls WITH Tyrannosaurus? And what about the ankylosaurs?
How did Triceratops die out in the first place?
A breaking point may have been reached
around K-T time if many T. rexes did wander into other paleoenvironments,
reducing local predation pressure and causing Triceratops, etc. polulations
and food demands to increase even more.
T. rex evolved when the regression began, AFAIK, or slightly earlier. According to your logic, it should have emigrated much earlier. The regression took 4 Ma, stretching the K-T boundary.
Or perhaps a wetter climate toward
the end favored re-colonization of grazed areas by ferns more than previously.
What is your evidence for a wetter climate at that time?
      But the main point here is that an impact is not necessarily implied
by a fern spore spike.
 
No problem at all for the impact theory, which rests on whole formations of evidence.
At least two alternative causes have been confirmed
by direct observation.  An alternative source of iridium--volcanism--has also
been confirmed,
LOL. Hawai'i-type volcanism produces slight amount of iridium, but not osmium with extraterrestrial isotope ratios. And so on. I'm sure the archives are full of discussions about that.
whereas the link between such evidence and impacts is
probably mostly conjectural.
"probably mostly conjectural"? I'd say "as sure as birds are dinosaurs" and recommend once more the book Night Comes to the Cretaceous.