Re: Question, what do things do when they freeze?


"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.

When 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 was
beginning to cool, and has continued to cool.

Once it segregated into layers of varying
density did the diameter change?

Why would it? The overall mass would remain the same.

Was 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 for
a very long time.

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?

George


.

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