[Bulk] Re: [Rockhounds] Survival of the firmest - Scientists say rocksevolve too

[J Bryan Kramer]

The Larimide Orogeny was supposed to have pushed the Wyoming mountains up to
40,000 feet more or less and the mountains farther south around El Paso up
to 25,000 feet. If I recall my old geology. So just the roots of those peaks
remain today.

You need to head up to the Canadian Shield or Greenland to find really old
rock. One thing that impressed me from geology was that we talk about all
these periods but the vast majority of the earth's history is unknown and
all lumped into "Precambrian". Almost all that is left is just relatively
recent material from the final 10% of geological history, except for a few
spots.

The Adirondacks are supposed to be fairly young they are just formed of rock
that was buried 30 km deep a gigayear or so ago, metamorphosed and then
uplifted during the Tertiary. Right about the same time as the Larimide was
going on or maybe later.

<http://gretchen.geo.rpi.edu/roecker/nys/adir_txt.html>

BK


On Mon, Dec 1, 2008 at 20:59, jabac <jabac at hal-pc.org> wrote:

> Dora Smith wrote:
>
>> Haven't we known for a long time that the hardest rocks resist erosion?
>> Yup, they last the longest.  This is why granite from the foundation of the
>> Earth's crust can be found in the Adirondacks (New York).  I had to consider
>> that something less obvious could lie behind the subject heading, but thanks
>> someone else for saying that it isn't new.
>>
>>  Harder rocks do "last longer" as you say, but consider that the mountains
> of Eastern North America are much older than those of the West, and a whole
> lot more material had to be removed from them to expose what we now see.  A
> great deal of the center of the country to the depth of many miles is now
> covered with the remains of that erosion. So maybe hard rocks resist
> erosion, but it took a long, long time to expose what is now visible. The
> Appalachians and Laurentians are showing us their remaining roots, not the
> proud crests they once were.  They are incidentally not from the foundation
> of the Earth's crust, but were the result of the collision of two plates
> some time in the past. If there are any "ur-rocks" around the East coast of
> North America, they are buried many miles below the present surface.
>
> Consider also that mountain ranges do not just arise and say "Well, here we
> are..."  They may be thrust up continuously over millions of years,  and
> simultaneously worn down so that the  average elevation only suggests the
> amount of material involved. Those hard rocks are eroding fast enough to not
> rise out of sight. Similar to the deposits in the East, the Great Plains in
> the West all the way to the Mississippi and the Gulf Coast are covered with
> the remains of the hard rock eroded from the Rocky Mountain Uplift.
>
> Again, consider granite, the very metaphor of "hard rock"; it clearly and
> quickly shows itself being eroded in its rounding and discoloration of the
> first few inched of exposed surface.  Were it not for that, the whole
> character of the West and the Western Movie would be different, a lot more
> jagged and rugged, maybe more "primitive"...(? )
>
> Even the Himalayas, which are the result of a huge upthrust from the Indian
> plate against Asia in a relatively short geological time, have not risen out
> of sight, so to speak. And the higher they go, the more wind and water ice,
> the most effective agents of erosion work on them. (All because water
> happens to have more volume as a solid than as a liquid. Curious, no?)
> Maybe the point is that sooner or later, almost all the rock that is
> created and exposed is eroded out of existence. I should think that the
> Canadian Shield is one of  if not the last remaining exposed "original"
> pieces of rock on the planet(except for odd pieces here and there); the rest
> have long since been transformed into newer things or had their core buried
> under the results of ages and eras of uplift and erosion. We have to
> appreciate something that is very hard to comprehend, and that is how vast
> and staggering is the span of geological time. If we were to have a life
> span of several million years, things would seem to change much more quickly
> than they do, and even then geological time would seem incredibly long. How
> fast is fast? It depends on the unit of measure, I guess.
>
>> Biologically produced rock isn't an example of survival of the firmest -
>> LOL, not hardly.  Usually it's just newest and closest to the surface.
>> Is the point an ecological idea that the geological character of the
>> planet has evolved over time?    Problem there is it isn't a geological
>> principle. And no new facts, just a new way of looking at what was already
>> known.
>>
>>  Mineralogically speaking, who knows? There is no question that the whole
> character of the planet would be entirely different without the long term
> presence of  20 to 25% of free oxygen in the atmosphere. On the other hand,
> if it were not so, it's not likely that we would be here to speculate on the
> finer points of any question. Life is interactive with its environment. So
> be it.
>
>
>  Yours,
>> Dora Smith
>> Austin, TX
>> tiggernut24 at yahoo.com
>>
>> --
>>
>
>
>
>
> john
> --
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-- 

""It often seems to me that the night is much more alive and richly colored
than the day."

                      Vincent van Gogh
J Bryan Krämer
North Florida, USA
photos at:
http://pbase.com/photoburner


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