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

[jabac]

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