Talk:Mantle (geology)

From Wikipedia, the free encyclopedia

Contents 1 etc 2 exploration 3 Stubbed this 4 Comments 5 Exploration

[edit] etc

both the upper and lower mantle both deform by thermally activative diffusion and dislocation creep. both are solid but both deform. neither of them are "semi-molten" and both behave like fluids on long timescales.

--195.96.247.34 09:23, 3 November 2005 (UTC)From Isak Avramov Avramov@ipc.bas.bg Avramov

TWO IMPORTANT QUESTIONS

I have the following two questions:

1. The Mantle composition given in the table to the article is quite widespread. However there is a problem. One can see that the amount of oxygen atoms must exceed the overall number of all other atoms. What is the nuclear reaction that produces so much oxygen atoms. I can understand the enormous amount of H and He in the universe. The most stable atom is that of Fe, so there is also a lot of it. But why oxygen. It seems the assumed composition is wrong. The core though, is the size of the moon.

The extra iron is located in the core. Estimates of the total Earth composition are 35% Fe, 30% O, 15% Si, 13% Mg... It is thought that much of the iron sank to the center of the Earth in the "Iron Catastrophe" early in the history of the Earth. (see the book "Earth" pp.12-13 by F. Press and R. Siever, for example).

The question was why the amount of O exceeds the overall amount of all other elements (exept Fe) Avramov

It turns out that the Earth's composition is the same as that of the solar nebular less a lot of hydrogen and other very volitile stuff. Oxygen in the (hot cooling) nebula would have formed silicate minerals and so not have been removed to the outer solar system as much as hydrogen was. So why oxygen in the nebula? Oxygen is one of the major products of small-ish stars, not all the stars that produced the elements that formed the nebula were large enough to produce iron. Andreww 07:29, 14 November 2005 (UTC)

2. The article states: “Due to the temperature difference between the Earth's crust and outer core there is a convective material circulation in the asthenosphere.” The appearance of convection depends on Rayleigh number. Can you imagine what must be the temperature gradient for convection appearance if viscosity is 10^22 Pa.s.

Ok, the article is wrong: the whole mantle is convecting not just the asthenosphere. You can estimate the Rayleigh number quite easily; the other numbers needed are the density (4000 kg.m^-3), thermal expansion (2*10^-5 /C), thermal diffusivity (10^-6 m^2.s^-1) and it turns out to be about 3000000 (see "Dynamic Earth" by Davies pg.218). The reason convection dominates is, of course, that rocks are really bad conductors of heat. Andreww 10:25, 3 November 2005 (UTC)

Hello, I'm wondering whether the hot temperatures of the crust exist because of conduction from the mantle or from radioactive decay of naturally present isotopes? is there debate on this topic? I haven't found anything relevant on wikipedia nor can i get a conclusive answer from other sources... thanks for ur help. Alex

Francis Birch's group at Harvard was apparently the first to find that there is a simple relationship between local deep crust temperatures and radioactivity in the crust itself, though radioactivity does not account for all of the temperature difference. The simple equation they derived is commonly used to infer how much heat is input into the crust from underlying convection by removing the contribution from radioactivity. Basically, it is A+B, where A is due to radioactivity (which can be measured), and B is due to heat input from the mantle.

[edit] exploration

should mention be made of the first attempt to drill to the mantle? See here: http://www.physorg.com/news9073.html

Done, please check/correct. Any idea on how they can claim to reach mantle rock at 'only' 7 km below seabed? --danh 16:30, 17 December 2005 (UTC)

Because they are aiming for the Moho and you can only detect that (so far) by seismic. It's thin ocean crust, not thick continenal crust. So you don't need to drill 70km, just 7. You may be missing the whole point, which is to investigate the moho, and what causes it, not to drill the mantle and discover "OMGZORZ there's ultramafic rocks and they're hot", because that's implied from 1) mantle xenoliths and xenoliths and 2) the fact that magma comes from the mantle. Rolinator 05:59, 27 December 2005 (UTC)

[edit] Stubbed this

The reasons I've stubbed this are;

1. The article is poorly set-out
2. There is little information on what evidence has been accumulated for the definition of the "mantle"; seismic, petrology, magmas, etc etc
3. It hardly even does justice to the Moho, or Mohorovicic.
4. The definitions are overly simplistic (even if a simplified summary is put up front for non-geologists and the layperson) and could do with a lot of work, cf, plastic flow and plate tectonics.
5. The lithospghere being aboutl 1/2 of what geology is concerned with aside from pretty minerals and fossils, is an important thing to get right and do it justice. This is pretty embarassing when there's 50 pages on abiogenic oil...

Rolinator 06:05, 27 December 2005 (UTC)

[edit] Comments

This article needs serious work. The mantle is the most important part of Earth (the crust, atmosphere, core, and ultimately life are all derived from it, after all, and it essentially controls the dynamical evolution of the Earth, including plate tectonics), yet here is a wikipedia article discussing it in complete shambles, not even up to snuff for an introductory geology level. I feel impelled to instigate a complete re-write, while not jettisoning everything in it (rather incorporating as much as possible). However, it is appropriate to pose the question here first rather than simply going about and doing a major overhaul of the page. Any comments? Objections?

—The preceding unsigned comment was added by 193.52.24.125 (talk • contribs) 23:03, 2 August 2006.

Go for it. The article is definetly in need of some serious help. Vsmith 23:14, 2 August 2006 (UTC)

I fertilized it and tied it to a trellis. Grow! Grow! (SEWilco 05:17, 16 September 2006 (UTC))

[edit] Exploration

Where did you get the source "thousands of square miles"? Both sources quoted state "thousands of square kilometers" (kilometers are smaller than miles). This source states that it "is irregularly shaped, about 30 miles long and perhaps that distance or more at its widest". That gives it a maximum area of 900 square miles (if it were a perfect square), and it is probably much less than that.

PK9 23:19, 6 March 2007 (UTC)

Fixed. Vsmith 03:52, 7 March 2007 (UTC)