Talk:Mantle (geology)

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.

Note about temperature

Conduction questions aside, a note should be made about the uncertainty of the temperature throughout the mantle, specifically at the CMB.

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)

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) Hello I will chuck all of you in a river — Preceding unsigned comment added by 70.108.31.137 (talk) 01:00, 28 September 2011 (UTC)

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?

—Preceding unsigned comment 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))

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)

Asthenosphere?

Other articles refer to different ways of classifying layers within the mantle.

The Lithosphere/Asthenosphere system (necessarily) muddles the older distinction between crust and mantle, but this article doesn't make the situation any better to a lay person trying to develop a basic understanding.

Some attempt should be made to reconcile the different classification systems - and if this is not possible to at least acknowledge their difference while attempting to address the genesis of this disparity (these disparities????) Scientific disputes can be really interesting . . .

JP 00:06, 18 July 2008 (UTC)

So the distinction is that the crust and mantle are a compositional boundary, while the lithosphere and asthenosphere are mechanical boundaries. The Lithosphere contains the crust and mechanically-rigid upper mantle; together these form tectonic plates. The asthenosphere is the low-viscosity layer beneath the lithosphere, and is also part of the upper mantle. Hope this helps - I'll add this to the article when I get around to it; have had a little too much Wikipedia for the moment. Ping me if I take too long. Awickert (talk) 09:49, 24 March 2009 (UTC)

To complicate things further perhaps, the lithosphere-asthenosphere boundary (apparently known as the LAB, a new acronym for my collection) within the mantle occurs at about the 1600K (normally approximated to 1300 °C) isotherm beneath which the mantle is weak enough to convect. This occurs at constant temperature due to the flow-law for peridotite being virtually insensitive to pressure. Some workers in geodynamics refer to the lithosphere as being both a mechanical and thermal boundary layer, distinguising it from the crust which is a chemical boundary layer and only sometimes apparently a mechanical boundary layer (so yet another way of describing the layering of the mantle). I think that we may need sections describing the chemical boundaries separate from the thermo-mechanical ones. I will also give this some thought over the next few hours/days/weeks/..... Mikenorton (talk) 22:02, 24 March 2009 (UTC)

RFC notification

Resolved: 3 contributors banned as master and socks. RFC closed. Awickert (talk) 20:43, 23 March 2009 (UTC)

I have initiated a request for comment on the Expanding Earth hypothesis at Talk:Expanding Earth#Request for Comment: Expanding Earth and Plate Tectonics. Please leave a comment there, or a statement if you were involved in the debate. Thank you, Awickert (talk) 05:08, 22 March 2009 (UTC)

Measurements

The measurements in the article are not realitive to the measurements in the other articles. "These layers (and their depths) are the following: the upper mantle (33–410 km) (20 to 254 miles), the transition zone (410–660 km), the lower mantle (660–2891 km), and in the bottom of the latter region there is the anomalous D" layer with a variable thickness (on average ~200 km thick)[2][3][4][5]." Wikipedia, Mantle (geology) and "The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick[1] and is composed primarily of basalt, diabase, and gabbro. The continental crust is typically from '30 km (20 mi) to 50 km (30 mi) thick, and it is mostly composed of less dense rocks than is the oceanic crust." Wikipedia, Crust (geology). The measurements are the continential plates extend from 30 km to 50 km in one artice and another article says the upper mantle extends from 33 km to 410 km. Please note the italics. —Preceding unsigned comment added by LouisSS13 (talk • contribs) 19:07, 5 July 2009 (UTC)

Also, how is the mantle about 2,870 km thick when the mantle only stretches to 2891 km deep? —Preceding unsigned comment added by LouisSS13 (talk • contribs) 19:22, 5 July 2009 (UTC)

Image

I think the "to scale" and "not to scale" labels on the top image need to be moved around. As I understand it, the full hemi-sphere image is to scale, whereas the segment is not, but the positions of the two labels do not make this clear. Kernow (talk) 13:45, 18 June 2010 (UTC)

Higher Elevation over Hotspots due to Buoyancy?

There is a sentence that mentions that areas of the Earth's surface located over hotspots are predicted to have higher elevation due to the increased buoyancy imparted by the hotter, lower-density mantle beneath. However, this prediction does not match current observations. While known hotspots often exhibit higher surface elevation, the causes are not known to be due to mantle buoyancy. For example, the Hawaiian hotspot's current surface manifestation (Mauna Kea) exhibits high elevation due to volcanic accumulation. In fact, the crust is actually DEPRESSED nearly four miles here due to the weight of accumulated material, quite contrary to what is claimed in the section I am disputing. While there is evidence that mantle plumes can explain large-scale elevation anomalies such as the African superswell, this hypothesis has not yet been proved and much of the evidence used to support it is conjectural. I propose that this sentence be removed or at least acknowledged to be a controversial claim, but I would appreciate the input of editors with more technical knowledge of the subject before making the change. 63.115.56.33 (talk) —Preceding undated comment added 19:17, 25 January 2012 (UTC).

Furthermore, upon investigating the source cited to support this claim, I found that it is a book chronicling the controversy surrounding claims such as this one, going so far as to acknowledge in the description of the book that the hypothesis has undergone numerous alterations over the past 30 years to account for observations that do not match its predictions, ultimately becoming what amounts to an unfalsifiable hypothesis. As Wolfgang Pauli once said, "Not only is it not right, it's not even wrong!"63.115.56.32 (talk) —Preceding undated comment added 19:38, 25 January 2012 (UTC).