Re: Burgess Shale college project

Sapient Fridge <use_reply_address@xxxxxxxxxxxxxx> eyed the audience and
in choked emotion intoned: news:aGuPcs3dhUUJFwcE@xxxxxxxxxxxxxx:

In message <Xns9B7CCA88F4144goodfuckinglucklibe@xxxxxxxxxxxxxx>,
Krubozumo Nyankoye <libvet@xxxxxxxxxx> writes
Sapient Fridge <use_reply_address@xxxxxxxxxxxxxx> eyed the audience
and in choked emotion intoned: news:bWpC0JrbATTJFw1P@xxxxxxxxxxxxxx:

I recently completed a college project doing a web page on the
Burgess Shale. If anyone is interested then the web page is here:

http://www.spamsights.org/cambrian

I learned some of the science from posts to talk.origins, and some
posts sparked my interest in other areas - so a huge thank you to
everyone who inadvertently helped me pass :-)

Any (science backed) comments or corrections welcome.

Your site is well done. I have one criticism of the site design
itself. I think you should provide at minimum links on sub-pages to
preceeding and following pages in the original logical order. Better
perhaps would be links to all pages present on every page. I know
this is a quibble but it does make navigating around the site much
easier for the reader.

Yep, that's a good idea. I'll do that when I next do an edit, I also
need to take on board Harshman's point that some of the phyla appeared
before and some after the Cambrian (rather than them all appearing at
once.)

May I suggest that you do a little more investigating and make mention of
some of the other similar fauna that occur in other locations. I am being
deliberately coy about this but it would help you to respond to Harshman's
point.

I would also like to know at what academic level this project is
being offered.

Hmm. The course I'm on is evening classes and equivalent to a first
year of a degree course (eventually), so probably not that high. I'm
doing the course purely for fun rather than need of another
qualification. I tried to aim the pages at the layman who knows a bit
of science but who isn't an expert, it's clearly not a serious
academic study.

That being the case much of what I have already mentioned is nitpicking.
There may still be some points you would like to address so I will read
through the site more thoroughly. There is much there on which I am not
qualified to comment (e.g. Harshman's comment I am not a paleontologist).

I do, however, still think that even a layman's presentation should be as
rigorous as possible within the limits of clear and concise expression. You
may or may not be aware that there is a vast amount of not only inaccurate
but outright mendacious information available on the web. While recognizing
the need to simplify and organize information for the lay public in a
fashion that is both palatable and easily understood, I think it is very
important to avoid any discourse that could be considered incorrect.

In that context I would also prefer that you rely less than you do on
wikipedia. It is a good source to be sure as a starting point, but you have
a certain responsibility to your readers to do more than simply cite it and
move on. You should, at the least, if possible, check the original sources
cited in wikipedia itself, read them and make a determination whether you
agree with the interpretation and context of the reference they have made.
If indeed, there is no reference to a point in a wikipedia article, then
you probably should not use it.

I ask because differing degrees of pedantry are appropriate to
differing levels of expected expertise. For example: The first
sentence of the fifth paragraph on the geology page. "Note that deep
sea fossils from the Cambrian period are rare because plate tectonics
creates new ocean crust at oceanic ridges and destroys it by
subduction at continental boundaries." Not all subduction occurs at
oceanic/continental plate boundaries.

Doesn't it? My understanding is probably fairly basic but I thought
that when oceanic crust hit continental crust it sank because it is
denser, thus giving subduction zones. Most (actually I thought all)
of the subduction zones around the planet seem to follow that pattern.
What are the other mechanisms?

As was pointed out in the following comment, there are also ocean/ocean
collisional environments where one oceanic plate is subducted beneath
another. The foundering due to density hypothesis is widely favored in such
cases. There are also continental/continental collisional zones, India and
south Asia are a good example. Since continents often have "shelves" that
are sub-sealevel the result of such a collision can mean marine rocks found
at present day elevations of over 8,000 meters. It becomes even more
interesting when ocean ridge environments collide with continental plates.
Two such environments occur in western N. America.

All of these situations can result in oceanic sedimentary rocks becoming
"obducted" onto continental margins resulting in the seemingly
counter intuitive juxtaposition of marine rocks with rocks of very
different origins and ages.

The point of the lost deep sea fossils was covered on page 133 of
Simon Conway Morris's book "the Crucible of Creation" ISBN
0-19-286202-2 (highly recommended btw.)

Re discussion of deep sea trilobites:

"Only the remnants of this trilobite distribution survives, tacked on
to the edges of the continents, because nearly all this [deep] sea
floor was subsequently destroyed. The principal mode of destruction
is by the processes of subduction, whereby the ocean floor of one
tectonic plate is forced beneath another"

It is quite true that the vast majority of the oceanic crust is eventually
subducted and we have no examples of "pristine" oceanic crust older than
about 200 mya. Yet we do have examples of more ancient oceanic crust that
have undergone varying degrees of metamorphism. Unfortunately metamorphism
tends to obliterate any fossils and much of these metamorphosed oceanic
rocks never would have contained fossils in the first place, even if they
had existed. You have to bear in mind, metazoan fossils occur only in rocks
roughly 550 mya or younger, or about 1/7th of earth's history.

Moreover,not all of the oceanic crust that is on a subducting
plate is necessarily "destroyed".

I know it can come back up again, seismic tomography shows that the
subducted slabs are mostly still whole.

Yes, subducted plates seem to retain their overall geometry to considerable
depths. However, those bits that "come back up again" do so in the form of
silica rich magmas forming strato volcanoes. Much later even more
interesting volcanics transport relics of prior ocean crust to the surface
but none of these preserve any evidence of fossils except in the case of
xenoliths of fossiliferous rocks they may transect during eruption.

Otherwise how would we have the Burgess
shale to study?

Because it was on the continental side of the plate boundary, although
below the water line...?

What is the mechanism that *preserves* portions of oceanic
crust without significant metamorphism?

That sounds interesting, do you have some more information on that? I
would have thought it would be mostly luck that some parts are deeply
buried and some aren't.

While it is largely a matter of luck if a fossiliferous rock is formed,
preserved relatively intact and subsequently exposed, the means by which
that occurs can be understood in some cases.

One mechanism is manifested most spectacularly in the western Andes.
Because the thick and at least partly indurated sediments lying atop old
dense basaltic ocean crust are less dense they can be "scraped off" in
significantly large wedges and undergo little dynamic metamorphism yet end
up resting atop older continental rocks. There are many other examples of
such "thrust belts" of varying age, some in the U.S. occur in Wyoming and
Montana. Another mechanism is that sea levels can fluctuate significantly
over geologic periods of time. In such situations significant marine
sediments can accumulate in continental areas that are inundated by shallow
seas and become exposed later with little if any tectonic component to
their occurence.

By submitting your work to review in this "forum", you obviously are
seeking constructive advice with respect to how you may improve and
expand your skills.

I had a variety of reasons for posting here, partly because having
done the work to pass my project it seemed a shame to just dump the
web pages on a CD to file in a drawer, and partly because I thought it
might spark some interesting threads on a subject that I'm interested
in and one that is reasonably on-topic for the group.

Well you must be relatively new to the group. Unfortunately although there
is a strong relationship between paleontology and related geological topics
there is also a vocal group of radical earth-science kooks who will no
doubt discover this thread by key word search and soon pounce upon it
rendering all useful discussion virtually impossible or too unappetizing to
continue. But we will continue for the present and hope for the best. I
sincerely hope that you are right and I am wrong in that respect.

That is commendable. However, without knowing what degree of
expertise was expected of you for this project, I am reluctant to
offer up otherwise legitimate criticisms unless you want to improve
both the site itself, and your own abilities in expressing in a
concise and clear way what are often, complex and difficult concepts.

If you would prefer, I can also communicate my comments on the site
to you via email instead of "in public".

I'm happy for either E-mail or public discussion. Part of the point
was to spark interesting threads and I'm not worried about my pages
being shredded publicly, if it raises the information content of both
my head and the group in general.

I may or may not redo the web pages though, it depends on the amount
of detail and work involved.

I hardly think it will be necessary to redo the web pages but what further
suggestions I offer will be in the spirit in which you intended your site
in the first place.

I hope you take this reply in the spirit
it is offered.

Absolutely

I take you at your word.

Cheers,


--
Here we may reign secure, and in my choyce
To reign is worth ambition though in Hell:
Better to reign in Hell, than serve in Heav'n.

.

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