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

From: Carsten Troelsgaard (carsten.troelsgaard_at_mail.dk)
Date: 03/14/05 

Date: Mon, 14 Mar 2005 21:40:17 +0100

"George" <george@wtfiswrongwithyou.com> skrev i en meddelelse
news:X8gZd.67618$r55.51532@attbi_s52...
>
> "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...
>
> <snip>
>
>>> 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.
>
> Significant water in the mantle would also change the average density of
> the earth. Since the average density of the earth is already known, the
> possibility of significant water in the mantle is not a reasonable
> assumption, and certainly is not supported by what is known of mantle
> mineralogy.
>
>
>>> From the slow EE
>>> standpoint, there is plenty of wiggle room here. We don't actually
>>> know when or even how the ocean water was added (volcanic outgassing,
>>> comets). The problem is greater for fast EE models.
>
> Although the oldest known rocks are less than 4.0 billion years old, the
> oldest known sand grains are radiometrically dated at 4.1 billion years.
> These grains are very hard zircons that were redeposited in sandstones
> millions of years after they formed as part of a volcanic rock suite
> (which no longer exists). It is nearly certain that when the oldest crust
> was forming in the earliest Archaean, there was likely not much water,
> because the crust would have been too hot. It is nearly certain that
> sometime after 4.0 billion years, there was significant quantities of
> water on earth.

> It is certain that the gneiss that occurs in Greenland and dated to 3.8
> billion years ago was formed from water-lain sedimentary rock, and so must
> be quite old, indeed.

My argument about 'too much water would be the consequence' has lost bite
though.

Carsten

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