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Re: Land Plants Origins Pushed Back



Yes, I was referring to the geologic time scale. I was contemplating that the
discovery of indisputable evidence for the existence of land plants predating 
the
advent of the Paleozoic era, might compel a restructuring of the classic time 
scale
we all know. A possible alteration would be to push back the Cambrian period to 
at
least 700 MY. This would reflect the new findings. Of course I'm no geologist 
either,
and I'm certain that there would be a host of other considerations determining 
the
justification of such a restructure. (There is a greater emphasis in the 
evolution of
animal life as opposed to plant life in the geologic time scale, for one thing.)


Ken Kinman wrote:

> James,
>      I'm not sure exactly what you mean by "timeline", but clearly if
> Precambrian fossils of land plants were found, timelines would have to be
> changed to show them originating much earlier.  But perhaps you are speaking
> of the actual subdivisions of geological time.
>      As far as changing the actual framework of Late Precambrian
> (Neoproterozoic) subdivisions and their ages (which is still rather fluid
> and inexact), I assume those will continue to be based more on the Metazoan
> fossil record, just as is the case with Paleozoic, Mesozoic and Cenozoic
> subdivisions.
>      But with the increasing evidence that many major faunal changes (mass
> extinctions) correspond with major impact events, it wouldn't surprise me if
> geological evidence for such massive impacts eventually became the basis for
> a more precise subdivision of the Late Precambrian.  However, since we are
> still arguing over the importance of Mesozoic impacts, I doubt that we will
> be seriously debating Precambrian subdivisions on that basis anytime soon,
> but I'm not a geologist so I may be underestimating the progress that may
> have been made on that subject.  So much going on and so little time to keep
> up with the explosion in scientific knowledge.
>         ---Cheers,   Ken
> *******************************************
>
> ?From: JAMES ARONIS ?Apollo@MLink.net?
> ?Reply-To: Apollo@MLink.net
> ?To: Dinosaur Mailing List ?dinosaur@usc.edu?
> ?Subject: Re: Land Plants Origins Pushed Back
> ?Date: Wed, 15 Aug 2001 12:15:17 -0400
> ?
> ?If indeed this molecular 'evidence' is paralleled with the discovery of new
> ?fossil
> ?records, will that necessitate changes made to the geologic timeline in
> ?order to
> ?reflect these new discoveries?
> ?
> ?Ken Kinman wrote:
> ?
> ? ? Eric,
> ? ?      Some molecular "clocks" are better than others, and the
> ?possiblility of
> ? ? skewing should be considered.
> ? ?       However, even if the dates are too early, it clearly points out
> ?the
> ? ? probability that there were primitive bryophytes (liverworts and
> ?possibly
> ? ? even mosses), fungi, and lichens on land during the Precambrian.  The
> ? ? question is if there is any trace of them in the fossil record, and if
> ?we
> ? ? look hard enough, I bet someone will find such traces eventually.  The
> ? ? fossil record is notoriously incomplete, especially when it comes to
> ? ? soft-bodied organisms.
> ? ?             -------Ken
> ? ? P.S.  I should make it clear that I do not buy Retallack's hypothesis
> ?that
> ? ? vendobionts were lichens.  However, there are some controversial
> ?Cambrian
> ? ? fossils of "fungi" that should perhaps be carefully reexamined in light
> ?of
> ? ? these new findings.
> ? ? ******************************************
> ? ? ?From: ELurio@aol.com
> ? ? ?Reply-To: ELurio@aol.com
> ? ? ?To: rtravsky@uwyo.edu, dinosaur@usc.edu
> ? ? ?Subject: Re: Land Plants Origins Pushed Back
> ? ? ?Date: Wed, 15 Aug 2001 09:11:55 EDT
> ? ? ?
> ? ? ?Here we go AGAIN!!!! There's ample evidence that rapid evolution can
> ? ? ?squewer
> ? ? ?the molecular clock bigtime. When the fossil record and the molecular
> ? ? ?"record" disagree on chronology, always go with the fossil record.
> ? ? ?
> ? ? ?eric l.
> ? ?
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