Re: sea levels many million of years ago?
- From: "don findlay" <don@xxxxxxxxxxxx>
- Date: 28 Dec 2006 03:32:46 -0800
neutrino wrote:
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?
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.
Carsten is of course quite correct. 'Continental subsidence' happens
because the Earth is cooling. As the oceanic crust cools, it shrinks,
and shrinkage pulls the oceanic crust down, as Carsten says. All
geologists know the Earth is shrinking in this way, that cooling down
is the essential driver for Plate Tectonics, ... and conversely when
the Earth warms up, the crust rises up.. Like at Spreading ridges. You
could imagine it as something like an accordion wheezing in and out -
shrinking and expanding as the Earth cools down and warms up (...except
of course that the Earth is not warming up, but mostly cooling down -
so it is set generally on a course of shrinkage - the continents at
least). And of course as the Earth shrinks, the water rises to cover
the land. This is why large parts of the continental shelf are now
covered with water. Some people think that the formation of ice at the
poles moderates this effect as water is taken out of the atmosphere/
sea to form the ice caps, causing regression of the seas, which
balances the contraction effect. This is why global warming is such a
concern, because the melt effect is immediate, whereas it takes quite a
long time for the Earth's crust to respond to warming. (as the Earth
gets warmer it expands, the crust rises up and the seas recede from the
land). The Himalyas, known as The Roof of the World, mark a time when
the Earth was once much much warmer (coal, ..dinosaurs in swamps
keeping cool on account of a fragile vascular system) and has since
warmed up, causing the crust to expand and a draw-down effect on the
seas to the tune of some 8000m. It is reassuring to know that there
is, as Carsten says, a cooling effect in progress now, pulling the
crust down and allowing marine transgression to cover the land.
Don't believe the nonsense of global warming getting put around now.
Well, at least it's not much to worry about. Cities and coastlines
might be submerged in the short term, but eventually they will rise
back up. No Worries.
.
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