Re: Plate techtonics and asteroid hits

first_name@xxxxxxxxxxxxx (Florian) wrote in
news:1i2jtrr.1d9yhc319o12yqN%first_name@xxxxxxxxxxxxx:

David Iain Greig <dgreig@xxxxxxxxxxxx> wrote:

One possible answer would be crustal buckling due to expansion, which
could well have pushed oceanic crust upwards.

That is one possibility.

But obduction also occurs if oceanic floor is pushed over continental
crust by a plume. The papuan ultrabasic belt is good example. See
Fig7, Kugler "Subduction and Overthrusting"
http://www.lulu.com/content/421591


Maxlow clais a constant
earth radius to 1.5Bya, but allows some folding may have occurred.

I just posted an issue in another thread - a planet of 1700km radius
has an escape velocity so low it could not retain an atmosphere.
So much for early life...

Except you failed to calculate the correct escape velocity.
So much for ... ;-)


yes but - the moon has an escape velocity of about 2.4 km/sec; a dwarf
planet with a 1700 km radius and mean density of 5.5 has an escape
velocity of 3 km/sec; Mars has an escape velocity of about 5 km/sec.
Thus the atmospheric pressure of such a hypothetical dwarf planet would
be much closer to that of the Moon (i.e nil) than Mars (roughly 1% of
earth's atmospheric pressure). While David may have misplaced a decimal
point, the correction makes very little difference in his argument - a
small early Earth ain't gots no atmosphere, and we KNOW that it in fact
did.

Further, now that I think about it, said small early Earth must have
had a spectacularly high heat flow, since it must have been REAL hot.
The present radius of the core is something like 3400 km (twice the
radius of the postulated early earth). So for the earth to grow to its
present size, not only do you have to add just bucketloads of molten
iron-nickel (four times the volume of the planet you started with), you
also have to add four times as many bucketloads of peridotite, and THEN
you need to add enough heat to keep the geomagnetic dynamo running
throughout. Not only do you need to add matter, you need to add hot,
glowing matter, some of it in a liquid state. And you still need to
explain the geologic and geochemical assymetry of Paleozoic suture
zones... the more I think about it the sillier it gets...

.

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