Re: Question, what do things do when they freeze?
- From: "George" <george@xxxxxxxxxxxxxxx>
- Date: Thu, 26 Apr 2007 21:19:40 -0400
"Jonathan" <write@xxxxxxxxxxxxx> wrote in message
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"George" <george@xxxxxxxxxxxxxxx> wrote in message
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"Jonathan" <write@xxxxxxxxxxxxx> wrote in message
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"George" <george@xxxxxxxxxxxxxxx> wrote in message
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Yes, but that occurred before the crust formed, and so the crust
could
hardly have overturned catastrophically as a result. And yes I think
that
convection has likely been going on deep inside the earth since it
formed
4.56 bya.
Some questions I have; the oldest part of the sea floor, due
to spreading and supposedly subduction, is only some
200 million years old. I assume the super continent broke
up and started drifting apart around then. What about
before 200 million years? Has sea floor spreading been
present since the earth cooled?
The oldest oceanic crust is about 3.8 billion years old, so yeah, it
appears that tectonic forces have been active, likely since the
beginning.
I'm sure some that old has been found, but according to
this MGG chart, in general, the ocean crust is no older than
200 million years.
http://www.ngdc.noaa.gov/mgg/image/crustageposter.gif
Johnathon, you have to make a distinction between current oceanic crust and
much older oceanic crust (that which is not a part of the current ocean
floors). If you want to find old oceanic crust, the current ocean basins
is not the place to look.
wasWhen did it start?
No one knows an exact answer to this question because the earth's
surface
has been so completely reworked that no original crust remains
unaltered.
But that tells me that it likely has been ongoing nearly since the
formation of the planet.
I've read the earth
absorbs more heat than it gives off, how does
that play into plate tectonics?
Is the atmosphere or the earth's surface, on average, hot enough to
partially melt rock all the way down to the moho? No? Next.
And what was
the diameter of the earth before it segregated
and was still of fairly uniform density?
No one knows, and is not likely ever to know. About all you can say is
that during the earliest days, when the Earth was accreting, the volume
likely increased. After accretion stopped, however, there is no reason
to
suppose that it continued to increase its diameter, especially since it
beginning to cool, and has continued to cool.
Wouldn't the layers that cooled have a lower density and create
a larger diameter as they cooled?
Umm, no. Rock expands (is less dense) when it is heated, and shrinks (more
dense) when it is cooled.
Once it segregated into layers of varying
density did the diameter change?
Why would it? The overall mass would remain the same.
Changing density, wouldn't that change the diameter?
The argument for density change would argue against expansion, since rocks
become more dense (and tend to shrink) when they cool.
forWas the crust ever fully rigid and if so, when?
Rephrase question.
On Mars it appears the northern half of the
planet was a sea, while the southern half
was highlands. Could that have been the case
on earth?
The Earth is not like Mars. Our planet's crust has remained active,
while
Mars' is, for all intents and purposes, tectonically dead, and has been
a very long time.
Well, what are the long term trends, is the earth cooling over
time or is radioactive decay causing it to heat up? If so are
they linear or cyclic changes? Is the earth's long term future
to become more like Mars or Venus?
Over time, the Earth's interior has slowly cooled. But so what? By the
time the Earth cools enough to make a difference, no one will be around, so
what's the point?
I've looked for most of these answers with
little success. If only half of these questions
have yet to be answered, I would say geology
is still in it's infancy as a science.
You must not have looked too hard. And Geology is a middle of the road
scientific discipline. It bridges the physical and historical sciences.
Yes, compared to the physical sciences, geology is rather young. So
what?
I guess the point I'm trying to make is that plate tectonics
has some holes of it's own as a theory.
Yeah? So? All theories have flaws, that's why they are theories and not
natural laws.
Especially with
showing conclusively that subduction closely equals
new crust from sea floor spreading.
Why should it? There is no reason to suppose that it would.
And because it
doesn't really give us a clear understanding of the
distant past.
It is the theory that best explains the data we have.
EE theory has an even bigger hole with
the missing mass, but I don't see where one idea is
so much stronger that a competing idea should
be dismissed out of hand for having a similar
lack of specifics.
Similar lack of specifics? EE doesn't explain anything, while PT explains
a lot of what we see.
My intuition is strongly inclined to say neither model
has it right.
So what? You're not a geologist, so why should anyone care about your
intuition with regard to geology?
George
.
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