Yes exactly ! At first I thought I had missed something while reading the article ! But it looks like I haven't.

The article does a nice job of explaining the 'roots' bit but says nothing of the stabilisation !! and I have no idea why the professional geologist did not comment on that part of the question at all.

Ciwan wrote: I have no idea why the professional geologist did not comment on that part of the question at all.

Probably because it made no sense to him and was unaware of the questioner’s ulterior motive.
The only thing that I could think of to comment on that part of the question would be that the continental crust is not stable as there are processes such as mantle plumes which enable the continents to be split apart by rifting. Nor does it stabilise anything it moves too as it gets pushed around as evidenced by the action of plate tectonics.
Also the very fact that mountains get built by continental plates crashing into each other and that the geological evidence is that tall mountains are very young features as they erode over time goes to show very little for the assertion of stability.
The assertion that mountains stabilise the Earth is therefore simply unsupported.

Haha Awesome. Thank You. I love it when the murky ideas in my head become clear. Thanks very much.

Spearthrower wrote:

Ciwan wrote:
I always thought the Earth's crust was stabilized (needs stabilizing since it is basically floating on Magma) by the nearly-uniform-equal pull of Gravity from all sides.

The crust is not floating on magma, nor is it really floating on anything.

The layer underneath the crust is called the upper mantle, and it is predominantly solid and rigid. The crust needs stabilising like the skin on an apple needs stabilising!

Is this the case? I have never heard that the mantle was solid, but mostly magma flowing slowly from the earth's hot core to the surface and back again (thereby pushing the continental plates around). If the mantel hadn't some viscosity it couldn't create mantle convection right?

True JoeB, and also in all the documentaries I've seen, they always show the Mantle as a very thick hot soup-like thing (Molten rock really), moving from the centre outwards then back in towards the centre (convention).

JoeB wrote:

Spearthrower wrote:

Ciwan wrote:
I always thought the Earth's crust was stabilized (needs stabilizing since it is basically floating on Magma) by the nearly-uniform-equal pull of Gravity from all sides.

The crust is not floating on magma, nor is it really floating on anything.

The layer underneath the crust is called the upper mantle, and it is predominantly solid and rigid. The crust needs stabilising like the skin on an apple needs stabilising!

Is this the case? I have never heard that the mantle was solid, but mostly magma flowing slowly from the earth's hot core to the surface and back again (thereby pushing the continental plates around). If the mantel hadn't some viscosity it couldn't create mantle convection right?

I don't really have any online references for this: just books on basic geology.

But the wiki link pretty much agrees with what's in my books:

http://en.wikipedia.org/wiki/Mantle_%28geology%29

The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core. Earth's mantle is a rocky shell about 2,900 km (1,800 mi) thick[1] that constitutes about 84% of Earth's volume.[2] It is predominantly solid and encloses the iron-rich hot core, which occupies about 15% of Earth's volume.[2][3] Past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface, upon which we live.[4] Information about structure and composition of the mantle either result from geophysical investigation or from direct geoscientific analyses on Earth mantle derived xenoliths.

The top of the mantle is defined by a sudden increase in seismic velocity, which was first noted by Andrija Mohorovičić in 1909; this boundary is now referred to as the "Mohorovičić discontinuity" or "Moho".[10][13] The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, an irregular layer with a maximum thickness of perhaps 200 km. Below the lithosphere the upper mantle becomes notably more plastic

Ciwan wrote:Let's say there were no mountains on Earth, and it was all flat ground (talking about the stuff above sea level) .... How would that affect Earth's crust overall ?

During all of the Mesozoic, there were actually next to no considerable mountain ranges.

dear giwan :

That page is an excellent answer to the first part of the question "When did we first find out that mountains had roots" but in no way shows that the second part "and that these mountains stabilised the earth" is even meaningful and therefore cannot justifiably be used by Muslim fundies in the way I suspect that it is repeatedly used by them

well said giwan , as a muslim allow me to share this with you there no versus in Quran that said that mountains stabilizing the crust or the earth , they mistranslated the Arabic world (RAWASI)
(stabilizer ) does not mean mountain at all . and who ever made this connection is way wrong even if he a Muslim AS a matter of fact ALLAH said in the Quran that he is one who put down the mountain deep in the crust (ARSAHA ) and they look like PEGS after word that it .
so the mountains ARE PEGS FOR THEM SELF

IN ARABIC there a big deference between
RWASI ( رواسي ) : reflect the ability and the force within to do thier job
ARSAHA ( أرساها ) : reflect the need and lack inner force

Ciwan wrote:True JoeB, and also in all the documentaries I've seen, they always show the Mantle as a very thick hot soup-like thing (Molten rock really), moving from the centre outwards then back in towards the centre (convention).

The mantle is solid (demonstrated by the propagation of shear waves from one side to the other of the Earth).
A solid can flow (especially in large masses) because of several mechanisms that occur inside and at the boundaries of crystals that make them change shape and actually move. These processes are fundamentally controlled by the temperature and deformation rates. Also you have a to take into account that this flows occur over geologic time scales. The common concept of flow and viscosity is related to liquids because they are the every-day-experience we have with flowing matter. But solids can flow as well.

JoeB wrote:I have never heard that the mantle was solid, but mostly magma flowing slowly from the earth's hot core to the surface and back again (thereby pushing the continental plates around). If the mantel hadn't some viscosity it couldn't create mantle convection right?

Actually the depth and connection of mantle convection with respect to the core is matter of debate. anyway both the mantle and the core convect.

To come back for a moment to the initial question: the stabilization of mountains. Stabilization in geology has only one meaning, as far as I know: "it does not deform since a long time".
Clearly the muslim article you read was misleading something about the roots of mountains. I think that mountain roots are unstable because of the lateral contrast in viscosity, density and thermal structure with mantle rocks. actually roots of orogens are the opposite of a stabilized crust during orogenesis. While for other reasons they can be stabilizing factors once orogenesis ended (i.e. after the active margin became inactive).

halucigenia wrote:Magma is generally produced at subduction zones where the oceanic plates are subducted into the mantle and also where heat "plumes" from the mantle transfer heat into the crustal rocks.

An interesting detail is the role of water. From here:

The subducting basalt and sediment are normally rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the subducting slab bends downward.[2] During the transition from basalt to eclogite, these hydrous materials break down, producing copious quantities of water, which at such great pressure and temperature exists as a supercritical fluid. The supercritical water, which is hot and more buoyant than the surrounding rock, rises into the overlying mantle where it lowers the pressure in (and thus the melting temperature of) the mantle rock to the point of actual melting, generating magma. These magmas, in turn, rise, because they are less dense than the rocks of the mantle. These mantle-derived magmas (which are basaltic in composition) can continue to rise, ultimately to the Earth's surface, resulting in a volcanic eruption. The chemical composition of the erupting lava depends upon the degree to which the mantle-derived basalt (a) interacts with (melts) the Earth's crust and/or (b) undergoes fractional crystallization.

It came as a surprise that the surface features of Venus are quite different from those of Earth; especially, there are no mountain ranges. The cause of the difference may be that Venus lacks water.

I am not a geologist, but I think that if the mountains have roots deep into the earth,then it is for sure act like an extension for the earth crust deep inside, ultimately it will increase the stability of the crust.I can compare it to a picture that you want to hang it on the wall ,you can use nails to stabilize the picture on the wall.nails is like the mountains, picture is the earth crust, and the wall is the earth itself. even if some says that we didn't here it from scientists, but this does not mean it is wrong. for example before longtime ago, scientists discover that earth is moving around the sun and they found the sun static(not moving).but with the advancement in the science they discover that the sun is also moving.so what I want to say even if the science didn't discover this it does not necessary means it is wrong.

mhib1987 wrote:I am not a geologist,

Then it might be a good idea to consult the work of those folks.

but I think that if the mountains have roots deep into the earth,then it is for sure act like an extension for the earth crust deep inside, ultimately it will increase the stability of the crust.

There is no such thing as a stable crust. It flexes and moves and cracks open and undergoes constant and unending change.

I can compare it to a picture that you want to hang it on the wall ,you can use nails to stabilize the picture on the wall.nails is like the mountains, picture is the earth crust, and the wall is the earth itself.

Trouble is there is not one land mass on earth that is nailed down and unmoving.

even if some says that we didn't here it from scientists, but this does not mean it is wrong.

Nope, if it was a scientist telling you something he's/she's going to have empirical evidence in support of his/her position and he'd/she'd be looking for a flaw that would render the finding void.

for example before longtime ago, scientists discover that earth is moving around the sun and they found the sun static(not moving).but with the advancement in the science they discover that the sun is also moving.so what I want to say even if the science didn't discover this it does not necessary means it is wrong.

Nope, empirical evidence gathered by direct observations is what tells us the idea of a stable crust is wrong.

RS

@theropod
Well, if by "stable" crust you mean that is not significantly deforming since a long time...well Cratons (i.e. continental blocks not deformed since 1billion years ago or more) are stable.

@mhib1987
Mountains have "root" in to the earth in the sense that crustal material (light, compared to mantle material) occurs at greater depth. Because of the Archimede's principle, high topographic elevation cause the depression of the "compensation depth" i.e. the depth at which pressure must be laterally equal. (see "Airy" part of the sketch below)

http://www.cas.umt.edu/geosciences//fac ... yPratt.gif

A rough comparison is the iceberg example. because ice is less dense than water it tends to emerge. the fraction of the ice emerging from the water scales with the density contrast between the two (about 1/10). So the ice has some elevation above the watertable and a "root" extending in depth into the water. The actual depth of the ice is the compensation depth.

Erakivnor wrote:@theropod
Well, if by "stable" crust you mean that is not significantly deforming since a long time...well Cratons (i.e. continental blocks not deformed since 1billion years ago or more) are stable.

No, I didn't mean stable in that way. Over time even those old old blocks move and bounce and shake. I don't call that, or indeed any part of the planet, stable. We live on a molten ball of rock with a slag covering on the outside. None of that slag is what I'd call stable. Even the core is out of a steady stable state as the magnetic pole reversals show. Yes, there may be parts of that slag that remains intact, more or less, over a very long time, but intact and stable are two different things entirely.

RS

Perhaps the author was confusing cratons with 'mountain roots'.

Ciwan wrote:Awesome ! Thank You for the informative post Halucigenia.

About the original post, the muslim guy was saying that Allah placed the mountains as Pegs to stabilise the surface of the earth !! Not sure exactly what that means though and I'm guessing neither does he.

Indeed, it's very unlikely that he does.

Keep in mind that the core of the planet is very hot, heat that I assume is left over from the planet's coalescence into a rocky orb from bits and pieces that gravitated into a primordial elipitical form ... out of which the earth aggregated to become a planet.

The heat that's in the core is constanly diffusing outward to soak the entire mantle in heat. Of course it cools as it diffuses but it's warm enough to keep surface rocks at close to 50F.

And as far as stablization goes, everything is connected so that the earth is one thing. core, mantle, crust, mountains, all part of one thing. And that thing is spinning on ts axis and although it exhibits some very long period wobbles (long duration precessions) they are largely inconsequential to humans. Other than these very minor perurbations, the Earth is a stable body and has been for a very long time. Even the primordial elipse of rocky material the earth formed out of could be said to have been stable.

But the earth does exhibit local instabilities all the time, we call them "earthquakes."

I realize that this thread is 3 years old, but regarding the question of whether mountains act as "stabilizers" to Earth's crust, there is actual scientific research that supports this notion. For example, the Seismological Society of America journal published this paper in 2007 which concludes in its abstract that "The effect of the mountains reduces the peak amplitude of ground velocity for some regions in the basin by as much as 50% in the frequency band up to 0.5 Hz. These results suggest that, depending on the relative location of faulting and the nearby large-scale topography, the topography can shield some areas from ground shaking".