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Author Topic:   Gradual cooling of the earth
Minnemooseus
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Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 16 of 19 (654525)
03-02-2012 12:54 AM
Reply to: Message 15 by anglagard
03-02-2012 12:29 AM


Re: Hate to disagree but...
Now in physics it is shown that a shear wave will not propagate through a solid...
I'm pretty sure it is "a shear wave will not propagate though a liquid". If it was stopped by a solid, how did it make it though the crust?
The rest of your post supports my perspective - I guess that's a "said solid, meant liquid" thing.
I'd check your source(s), but you didn't supply any.
Moose

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anglagard
Member (Idle past 836 days)
Posts: 2339
From: Socorro, New Mexico USA
Joined: 03-18-2006


Message 17 of 19 (654541)
03-02-2012 1:26 AM
Reply to: Message 16 by Minnemooseus
03-02-2012 12:54 AM


Re: Hate to disagree but...
You got me, a definite error on my part. Oh well, make mistakes, even dumb ones, but fess up quick.
As to sources you could try the wiki on Structure of the Earth, my original source is from memory of Physics and Geology by Jacobs, Russell and Wilson, the textbook for general geophysics at New Mexico Tech back in 1980. Don't think the physics or structure has changed much since.
I think some confusion may occur because the mantle is referred to as viscous in the wiki article, however that is not synonymous with liquid and does not act that way according to physics.
{ABE} Actually managed to get a D in the class, Schlue had high standards and graded on a strict Bell Curve, took it too early, was in Calculus 3 at the same time, competition already took electrical physics and burned Maxwell into the ground. Lowest grade carried until a few years later when managed to flunk structural engineering at UNM (how embarrassing, missed last day to drop, please don't ask me to design a bridge). But I feel I remember more about that one than many I made an A in later.{/ABE}
Edited by anglagard, : Just too chatty, past bedtime

Read not to contradict and confute, not to believe and take for granted, not to find talk and discourse, but to weigh and consider. - Francis Bacon

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xongsmith
Member
Posts: 2578
From: massachusetts US
Joined: 01-01-2009
Member Rating: 6.8


Message 18 of 19 (654642)
03-02-2012 3:02 PM
Reply to: Message 15 by anglagard
03-02-2012 12:29 AM


Re: Hate to disagree but...
Anglagard writes:
A minor point in an otherwise largely accurate description.
Rahvin writes:
Most of the Earth is still molten, and it's far from homogenous.
Hate to disagree, but I suppose there is a first time for everything.
Most of the Earth is solid. The structure from top to bottom is crust, solid mantle, a plastic layer in the mantle around 20-50km down but only a few km thick. 1800 more miles of solid mantle, a liquid outer core and a solid inner core. The mantle makes up the majority of the Earth by both volume and mass and it is solid.
The issue of where is "half-way" down can be troublesome. Math states that the volume of a sphere is four thirds Pi R cubed. When you first gut-think half-way down, you are dividing the earth into roughly 1/8ths and 7/8ths. The volumetric half way point down into a sphere is about .79R (the cube root of .5) from the center.
The earth is some 6371 km in R, average radius, (or about 3960 miles). This means that half of the earth is only below about 816 miles, something akin to the trip from Detroit to New York, well above Anglagards 1800 mile thickness of the mantle.
"Most" can be an "optical illusion" of sorts when not thought out.

- xongsmith, 5.7d

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xongsmith
Member
Posts: 2578
From: massachusetts US
Joined: 01-01-2009
Member Rating: 6.8


Message 19 of 19 (654643)
03-02-2012 3:13 PM


BTW, with 7+ billion people on this earth, it may not seem that there is an immediate danger in using geothermal energy (ala' Iceland, let's say). Not now. But what if we find a great way to harness the molten interior for billions of years? When I first saw the OP title, I thought this was a long-range assessment of a potential new human-generated danger. Eventually, could humanity survive on a cold stone?
Oh well.

- xongsmith, 5.7d

  
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