How come the ocean hasn't been absorbed into the ground?

billiards

So you're not saying that the Moho (crust mantle boundary) is the boundary to which water can penetrate? And hence the inference that water cannot penetrate into the mantle?

OK, that was my reading of your statement below...

In which case I have absolutely no idea what this statement is supposed to mean.

sophiecentaur

Will you guys stop squabbling please and try to answer the OP?
An answer could be of the form "There is very little water underground" or "There is much more water underground than in all of the Oceans" - or something in between.
That information would be useful to Flatland, I'm sure, and to me also.

billiards

No it's not typical, people speculate quantitatively, however the 2 sigma uncertainty is likely to be huge and I don't happen to know the numbers off head. The data about water content has to be inferred from geophysical measurements, of things like the electrical conductivity of the mantle, and the seismic properties. It's hard enough to make good geophysical measurements in the first place, because there is always a lot going on in the signal and the Earth is not a conducive beast. For example if you want the signal from the upper mantle you need to remove the crust signal because your instruments are always on (or above) the crust and so any signal from the mantle necessarily has to pass through the crust. Then these measurements are very indirect and need to be put in context using mineralogical data. It's very hard to convert knowledge of seismic wavespeed and electric conductivity into a number for water content. Partly because there are other things that can have a similar effect to water on your data, and partly because most of those things have not even been worked out in terms of the mineral physics.

sophiecentaur

Thanks for the reply. I totally sympathise about the lack of data. But you are basically saying that the answer to the original question is that we don't know?? That is a totally acceptable answer, btw.

billiards

How come the ocean hasn't been absorbed into the ground?

1) If you are talking about why the ocean doesn't disappear down cracks in the ground it's because those crack are already full of water and the Earth is not an infinite sink.

2) If you are asking more generally why do we have free water on the Earth's surface. I would say with the caveat that this is not my area of expertise so could be wrong, but here goes: Water does not fit into rock forming minerals at high pressures and temperatures, and under intense P-T conditions will cause the rock to melt. If the melt is buoyant (which I guess it normally is -- otherwise we wouldn't have water at the surface -- (incidentally that's not an obvious thing at all as some melts in the earth are not buoyant and sink)) then the water will be carried up to the surface. This process forms a cycle which sustains water at the surface.

How much water is there in the Earth?

This is a different question from the OP, but is interesting. I will have to do some reading to try to find out, note that there are many ideas about this so the answer will depend on who you ask.

sophiecentaur

I am pretty impressed by what's been found out about the Earth's structure, bearing in mind that we literally only scratch the surface. There is seismic info too, and magnetic. Amazing how recently Plate Tektonics was 'invented'.
From your answer, it seems that I wad basically right about the density factor, though.

OmCheeto

I am still of the opinion that posts on, or about, April 1st, should still subscribe to PF standards of excellence.

---------------------------------
because I am so stupid, I will invariably be sucked in.....
and where has that rabble rouser Flatland been since December...

OmCheeto

billiards, you missed a very important financial opportunity there. I would have wagered major bucks you were joking.

Just before leaving for work this morning I checked on this most ludicrous of ideas, thinking maybe that I had misinterpreted something, and discovered it is not a joke.

sophiecentaur

I wonder about this talk about water altering the melting point of rocks. Presumably we are talking in terms of extremes of pressure and temperature so perhaps the gut reaction may not be a reliable one. Mixtures often have lower melting temperatures than the individual constituents and the 'water' in question is not the wet stuff we take a bath in but could be like the mercury (liquid) that dissolves (amalgam) gold (melts at 1000C plus) at room temperature.
Is the water / rock thing SUCH a loopy idea?

billiards

If you want to know more about water in the deep earth, then this here review paper is a pretty good starting point:

Hirschmann. Water, melting, and the deep Earth H2O cycle. Annu Rev Earth Pl Sc (2006) vol. 34 pp. 629-653

(freely available here: http://cips.berkeley.edu/events/rock...Hirschmann.pdf)

With regards to the quantity of water stored in the deep earth:

sophiecentaur

Thank you for that link. Loads of it but very interesting and it shows just how much more complicated the system is than one might think.

OmCheeto

Wow. Don't have time to read the whole thing, but maybe the thread topic should be changed to: "What if one quarter of the ocean hadn't been absorbed into the ground"?

From my calculations, sea level would be ~800 meters higher!



Fascinating...

sheshank

I'll speak in very short sentences. The Earth's temperature rises every 300 mts deep by some extent (perhaps one degree or so). This happens when there is something to cover it up. For example, lets consider the case of digging up earth. If you dig up the earth under one of the highest himalaya mountains to the sea level and compare it with the sea, you'll find the change in temperature. So, when it rains all water find slopes and reach oceans. Water accumulate together. They can't penetrate more deeper because, if they penetrate they'll face heavy temperature and have to come up again in the form of vapors through the tiny perforations of the crust. So, all the water stay where they are.

Sometimes water also goes deeper, like few said in this forum and it happens to support some chemical reactions like Formation of Natural gas and Fossil fuels etc. But, not all water can be sucked inside the Earth. I guess I cleared the initial doubt asked

Guess I am right with my explanation. Correct me if I am wrong.

sophiecentaur

That's the obvious first reaction, of course. But mixtures have different melting and boiling points from their individual constituents so it is not unthinkable that water could exist (as water) despite the high temperatures at great depth.
What you can read on the links on this thread suggest that it isn't as simple as one might think.

sheshank

Chemically reacted mixtures have entirely different boiling and melting points. That's sure. Other kinds of colloids formed due to water's mixture with something else can never have temperatures greater than a some or little above its boiling point. Like, salt water vaporizes slower than pure water. So, colloids or mixtures can't enhance or influence the temperature to a very great extent. Yes, they enhance and influence, but very little. If, its solutions that form a mixture, then they both must come to earth's surface due to immense pressure. It just can't be! My common sense say this. I don't know what science speaks of this and to add, I am not a geologist. Its just an obvious thing in physics.

sophiecentaur

You don't need a chemical reaction between glycerol and water or between mercury and copper to change the melting point considerably.
You say that you are speaking as a Physicist (and so am I) but I, certainly, have little knowledge of the behaviour of substances at extreme pressure. Do you?

If you look at the phase diagram of water, it remains solid at very high temperatures when the pressure is high enough. I think we need to look in much more detail if we want to be able to hold a valid opinion about this. Personally, I'm open to any good information that turns up on this thread.

sheshank

By the word "Science" I mean to say not just physical or chemical or geological but any. That's why I mentioned that I am not a geologist and my common sense speaks what I mentioned.

I think there doesn't need any knowledge other than those few Gaseous laws of Robert Boyle and Charles. So, I proposed my 'common sense' based on this.

Water can never stay in solid form inside the deep layers of earth. Either it should be in the form of colloids (liquid form) or gaseous form. I don't have a confirmation whether the water is in gaseous form under the Earth. (If so, then there should be sesmic vibrations experienced all around the Earth, not just at the places where techtonic plates collide).

How much ever water tries to form a colloid its polarization (because its a non-polar solvent) can't cross more than 180 degrees. Anything more than 120 degrees of polarization is quite impossible without electric supply. Water needs to form heavy polarization with is fellow colloid in order to sustain such heavy temperatures. In that case water molecule simply breaks down rather than staying there completely polarized.

There are two cases where water may form colloids. 1) solid in Liquid 2) liquid in liquid.
If solid in liquid is the case, then water definitely stays away from the solid it is mixed with, since their densities vary by heavy amount which makes them impossible to mix, unless they react chemically. Its a kind of Adsorption phenomena. Even if they mix, water can't account for greater than 2-3% of the colloid just soaking it wet. Given the area taken into consideration (as radius sinks and so is surface area as we go deep), we find very little water in the deeper layers of the earth.
If liquid in liquid is the case. Liquid can mix with liquid only in case as mentioned above (polarization). If there is some material in the form of liquid at that particular (heavy) temperature and pressure, then it must have heavier energy due to brownian motion. We know, when such high energy molecules collide with water molecules of lower energy, they, obviously, are ejected out. This is the practical case.

I state again, I am not a geologist, nor a chemist, nor a physicist. I stated something out of common sense and my high school chemical sciences. There may be other factors taken into consideration which I am not aware of. If anyone cares to mention them, I'll be glad to know about.