Re: Plate techtonics and asteroid hits

From: don findlay <don@xxxxxxxxxxxx>:

df> Ernest Major wrote:
df> > In message
df> <1182891696.906039.126100@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, don
df> > findlay <don@xxxxxxxxxxxx> writes > >
df> > >Eric Rowley wrote:
df> > >> From: don findlay <don@xxxxxxxxxxxx>:
df> > >> <snip>
df> > >>
df> > >>> Ok,..Question:-If the ocean floors are consumed
df> > >>> (subducted) at the same rate as they are formed at the
df> > >>> spreading ridge (accreted) (*wherever* these are) how
df> > >>>would the ocean floors ever open in the first place?

df> > >> What makes you think they needed opening in the first
df> > >>place?

df> > > You mean there's another place they could have opened?
df> > > Come on, ..It seems an obvious sort of a question,.. what's
df> > > the obvious answer?

df> > There's several obvious answers.

df> > 1) Your premise is incorrect, in that it assumes that the
df> > areas of continental and oceanic crust can't change.

df> You mean the Earth can get bigger or smaller?

df> > 2) If the areas of continental and oceanic crust are treated
df> >as constant as a first approximation, it is still not
df> >necessary for area of oceanic crust on individual plates to
df> >be constant. (So the Atlantic can open and grow at the
df> >expense of other oceans, such as the Pacific.)

df> We return to the question of how the first ocean opened in the
df> first place

And so we return to the question of why you think it wasn't open
at the start?

df> > 3) And there never was a situation in which the whole Earth
df> >was covered with continental crust. (Oceanic crust predated
df> >continental crust, only oceanic crust is recycled at a much
df> >greater rate than continental crust.)

df> So you mean the original Earth was covered with ocean floor?
df> (It never did differentiate into a crust/ mantle/ core?

Are you serious?????????????????

The _outside_ of the earth was covered with ocean floor
(crust), the mantle and core are on the _inside_!

Eric


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