Re: sea levels many million of years ago?


"neutrino" <stuartr@xxxxxxxxxxxxxx> skrev i en meddelelse
news:1167059798.350996.18900@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
when you view a map of the planet - with the oceans removed, or even as
seen in Google Earth.. you get a clear view of the ocean floor, and
almost what I see surrounding most all land masses are what appears to
be the shoreline as it might have been many millions of years back -
for example the U.K would appear to have extended much further into
the Atlantic, and would also have been a solid land mass with
Europe..... Viewing New Zealand -you can imagine out to the east the
land mass would have extended well out to include the now - Chatham
Islands, aprox 800 km away.
am I misreading what I'm seeing in this - or WAS that the original
land? and original sea level of the time? if so I can only assume that
the sea level back then must have been very stable for a very long time
- else there would be more erosion and a less well defined "edge" where
land met the sea?

Your assumption about sea-level as course is not correct, or you should use
terms as absolute or relative sealevel. It's rather the continent that's
subsided than the ocean that's changed level. Ocean-crust is thin, 5-7 km vs
continental crust 25-35 km, and thus the cooling (the density and thus the
boyancy) has a larger effect on the ocean-crust, and it pulls the
continental edge down. The edges you see are tectonic of nature.
The visible structure in the Atlantic is a Cretaceous/Early Tertiary
rift-system.
Glacial low sealevel has exposed large parts of the North Sea between the UK
and Scandinavia, but this does not coinside with the edge on the
google-earth images.

Carsten

or :) am I way off the mark? but if right - then there must have been
a great deal of water locked up in the polar regions, and for a
considerable time... and therefore - just how long has it taken for sea
levels to get to where they are at present.



.

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