Re: Owen's Two-Phase Model of Earth Expansion

From: George (george_at_wtfiswrongwithyou.com)
Date: 03/15/05 

Date: Tue, 15 Mar 2005 19:40:52 GMT

"Matt" <matt.edwards@utoronto.ca> wrote in message
news:e25c654e.0503151049.7f2f0a5@posting.google.com...
> "Carsten Troelsgaard" <carsten.troelsgaard@mail.dk> wrote in message
> news:<42355f4f$0$68394$edfadb0f@dread14.news.tele.dk>...
>> "Matt" <matt.edwards@utoronto.ca> skrev i en meddelelse
>> news:e25c654e.0503131018.2165caf3@posting.google.com...
>> > "Carsten Troelsgaard" <carsten.troelsgaard@mail.dk> wrote in message
>> > news:<423233a5$0$21781$edfadb0f@dread14.news.tele.dk>...
>> >> "Matt" <matt.edwards@utoronto.ca> skrev i en meddelelse
>> >> news:e25c654e.0503111026.35d455ba@posting.google.com...
>> >
>> >> > I saw your earlier post, but now I can't spot it. I seem to recall
>> >> > that your comments were based on the fast expansion hypothesis, which
>> >> > I am not addressing here. Here is what Weijermars says about sea
>> >> > level drop in slow expansion model (.5 mm/yr):
>> >> >
>> >> > - at 4.8 Ga oceans were 6.3 km deep worldwide if the volume of water
>> >> > were the same as today
>> >> > - at 3.5 Ga when life first evolved oceans were 3.2 km above present
>> >> > levels
>>
>> The two numbers above matches a doubling of the surface-area .. unless you
>> add something from somewhere else.
>
> No. As the ocean basins form, water drains off into them. The height
> of water on the continents depends on the area and depth of the ocean
> basins. Now, I've done a calculation for slow EE at .5 mm/yr and it
> seems like there is not enough ocean basin formed at 3.5 Ga to justify
> Weijermars' numbers here. The depth of water on continents would have
> been greater than 3.2 km if it started off at 6.3.

Hmmm. As the ocean basins form...

Since they are basins, and the oceans are draining into them (where the water
was before the oceans form, you don't say), that would indicate that a large
portion of the earth's crust sank instead of expanding.

>> >> > - at 2 Ga Earth's radius went over 5500 km and ocean level was 1 km
>> >> > above present (time of red bed deposition)
>> >>
>> >> The first hit I get is your local rock dated 2,4 billion years old.
>> >>
>> >> http://www.ingentaconnect.com/content/geol/jgs/1984/00000141/00000002/14120235
>> >>
>> >> Red beds are generally considered intracontinental shallow
>> >> water/lakustrine
>> >> sands. In the above also containing evaporites.
>> >
>> > I don't see a problem here. If the oceans were 1 km above present at
>> > 2 Ga, then much of the continental area was submerged, with
>> > considerable area at shallow levels suitable for red bed/evaporite
>> > formation.
>
> < >
>
>
>> > I attended a lecture by Stephen Moorbath here relating to this. He is
>> > one who questions whether the isotope evidence is valid. There was
>> > some spirited opposition from some researchers from the opposing camp.
>> > I asked Moorbath what he thought the ocean levels were at that time.
>>
>> > He said that while it is commonly supposed that the volume of ocean
>> > water was not too different from today, there was not too much
>> > evidence to actually support this notion.
>>
>> I know of ice meteors. They will not end up in the mantle. I don't know of
>> meteors of hydrated silicates, but then again, I'm no astronomer.
>> Significant volumes of water inside the earth would change rock-properties -
>> Take a look at the dehydration at subductions in the PT model. It could also
>> be expected to alter the composition of vulcanic rocks. I don't find reason
>> to doubt that H2O will find it's way out, fast, otherwise it would be
>> reasonable to expect the process still present in hotspot & divergence
>> vulcanism.
>
> There is one school of opinion which holds that the Earth's oceans
> came from comets exclusively. Assuming that these comets arrived
> after the original boiloff of volatiles (George mentions a 4 Ga date),
> then various water levels would have existed after each comet arrived
> and deposited water. A maximum level of 6.3 km might have been
> reached, but before that happened sedimentary rocks could have formed.

But before any of that would have happened, there would have been impact basins
that would have held substantial amounts of water (and possibly could have
formed simultaneous with the creation of the oceans).

Relevant Pages

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