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What prevent water from going down further after certain level

by vrmuth
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vrmuth
#1
May23-14, 07:32 AM
P: 78
Hi i have this question in my mind for very long time ,what stops water on earth from going further down and down and reach the center of the earth ? i want to know the laws of physics that makes this possible .
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Borek
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May23-14, 07:55 AM
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You are not the first one to ask this question on the forum.

Think: what is the temperature deep under gorund? What form does water take there?
russ_watters
#3
May23-14, 10:28 AM
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The best way to look at this is more direct: take a shovelful of dirt and rock and throw it in a lake: does it sink or float?

russ_watters
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May23-14, 10:30 AM
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What prevent water from going down further after certain level

Quote Quote by Borek View Post
You are not the first one to ask this question on the forum.

Think: what is the temperature deep under gorund? What form does water take there?
These questions imply that earth should be littered with geothermal power opportunities.

The form the water would take if it got deep enough doesn't matter if it rarely ever gets anywhere close to deep enough.
Borek
#5
May23-14, 11:24 AM
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I am not saying this is the whole answer. I am just try to point to some obvious limit.

BTW, water vapor is one of the main components of the volcanic gases. But my bet is that its main source is crystalline water from hydrates, not just water.
abitslow
#6
May23-14, 01:47 PM
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Its easy to find out what the structure of the Earth is, grade school stuff: https://en.wikipedia.org/wiki/Structure_of_the_Earth
I apologize if this sounds condescending, but I will attempt to give you the science. All matter occupies space (has volume) and has mass. One way we characterize matter is by its density. On the surface of the Earth, the measured weight of an object is its actual weight adjusted for its buoyancy. (Other effects such as variations in Earth's gravitational field, and centrifugal forces are ignored here.) Oil floats on water, fresh water can float on sea water, most woods float on water. Why? It is because their density is less than the fluid they are floating in. A helium balloon will float in air, so will a hot air balloon, for the same reason. It can be confusing to think about things like fluids, gasses, liquids, solids, crystals and molecules. If you take equal volumes of alcohol and water and mix them together, the total volume decreases, but only by a couple of percent. The mass of the two liquids adds up exactly to the total mass (allowing for any spills or losses). Mass is conserved in the everyday world, and volume is often "almost" conserved for liquids and solids. Volume is not at all conserved for gasses.
I hope its no surprize to you to learn that a rock sinks in water. (assuming its density is greater than the water's). Putting that same statement another way, a rock will displace the water and drop. If I were to do the opposite experiment, and pour water into a container holding a rock, I would find that the water does not displace the rock. If I were to do the same experiments with sand, I would find the same thing, that the sand displaces the water and not the other way around. But I might also note that the water "soak in" to the sand. If I were to measure the density of the sand and compare it to the density of quartz (which is the crystalline material most sand is made from) I would find that the sand is a LOT less dense than the quartz. Why? Well, one clue is that when I let water soak in, I might actually be able to see the air bubbling out of the sand. If I did the experiment in the right way, it would be easy to "catch" this. So, sand displaces water, water displaces air. Its all about density. Now, back to your question: "Why doesn't water displace rock and flow to the center of the Earth?" If that is what you meant, then hopefully the answer is obvious, now. But maybe that's not what you meant, instead your question was:"Why doesn't water displace the air in the Earth's Crust and Mantle and Core and flow to the center of the Earth?" Well if you read the Wikipedia article, you'd know that the Mantle and the Core are liquid rock and liquid metal, but perhaps I have to mention that both are much more dense than water? So, that leaves us with the question: "IS there air in the Earth's Crust which can be displaced by (denser) water?" The answer is: Not much, unless its trapped (like water is in a bottle), water will displace it. Meaning there is a lot more water in the Crust than air, and of course a lot more rock there than water.
D H
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May23-14, 02:51 PM
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Quote Quote by vrmuth View Post
Hi i have this question in my mind for very long time ,what stops water on earth from going further down and down and reach the center of the earth ? i want to know the laws of physics that makes this possible .
First off, please read this thread: http://www.physicsforums.com/showthread.php?t=564079.

There is *no* way that water could reach the center of the Earth. The second law of thermodynamics forbids this. If you look at a diagram of the Earth, you will see that it comprises a solid iron inner core, a molten iron outer core, an inner mantle, an outer mantle, and a crust. The densest stuff is at the core, the least dense stuff, in the crust, is at the surface. Why is the Earth layered so? The answer lies in entropy, energy, and the second law of thermodynamics.

A hypothetical homogeneous Earth in which all the atoms and molecules that form the Earth are evenly dispersed would have a much higher gravitational potential energy than does the real differentiated Earth. The differentiation of the early Earth released an immense amount of energy in the form of heat. That increased entropy. If there's a path from one state of a system to another state that increases entropy and if there is a way the system can take that path, it will. Systems tend toward a state that minimizes potential energy.

Water migrating down to and then into the core would drastically violate this minimization of potential energy. It just can't happen.

What can and does happen is that water seeps into the cracks in the crust. This is particularly important in the crust that underlies the oceans. Oceanic crust is instead constantly being recycled. New oceanic crust arises at the mid-continental ridges, gets pulled and pushed across the oceans, eventually to dive back into the Earth at subduction zones. Except for ophiolites (chunks of oceanic crust that got stranded on land), there is no old oceanic crust. The crust underneath the oceans is rather young, geologically speaking.

The subducting oceanic crust is fairly saturated with water. Most of that water is expelled in short order in the form of volcanic eruptions. Water is the biggest constituent of the immense amounts of gas emitted by volcanos. A small amount of that water combines chemically with the rock, and some of that rock dives into the mantle. How much water the mantle holds is an open debate. Some say a lot, some say very little. What all geologists agree on is that the amount of water on the Earth's surface has been remarkably constant for the last three billion years or more. The rapid turnover (rapid in a geological sense) means that the Earth reached a steady state in terms of the amount of water on the surface versus the amount of water stored underground within a billion years after the Earth formed.
vrmuth
#8
May26-14, 05:43 AM
P: 78
Quote Quote by D H View Post
First off, please read this thread: http://www.physicsforums.com/showthread.php?t=564079.

There is *no* way that water could reach the center of the Earth. The second law of thermodynamics forbids this. If you look at a diagram of the Earth, you will see that it comprises a solid iron inner core, a molten iron outer core, an inner mantle, an outer mantle, and a crust. The densest stuff is at the core, the least dense stuff, in the crust, is at the surface. Why is the Earth layered so? The answer lies in entropy, energy, and the second law of thermodynamics.
I am a math teacher , i know only some basics knowledge of thermodynamics and physics , so i sort of understood what you say here , but if you make it simple ..will be great
Borek
#9
May26-14, 06:10 AM
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Imagine huge water ball surrounded by shell made of heavier materials. This system is unstable, shell pieces will want to sink down. System will become stable once the shell gets to the center. Now just generalize to many materials of different densities.

In general, for a system composed of many materials with different densities, the stable configuration is the one with the heaviest (most dense) materials in the center, surrounded by concentric shells of the lighter and lighter materials. Water is relatively light, so it tends to be forced up by heavier materials sinking down.

Now, you can think in terms of water being forced into the cracks, and sinking down. That works only close to the surface, as technically water displaces air, which is lighter. However, when you go deeper, there are no cracks, they are closed because the material is hot and under high pressure.

Definitely this approach is better than mine (I don't think it falsifies my conclusions, it just makes them irrelevant in the grand scheme of things ).
vrmuth
#10
May26-14, 07:17 AM
P: 78
Quote Quote by Borek View Post

Now, you can think in terms of water being forced into the cracks, and sinking down. That works only close to the surface, as technically water displaces air, which is lighter. However, when you go deeper, there are no cracks, they are closed because the material is hot and under high pressure.
wow !! that's what i exactly wanted to know thanks , one more thing ....when water reaches to touch the heavy materials which are so hot what happens ? water becomes vapour but the water in the upper layer will cool it right ? can you please throw some light on it
Borek
#11
May27-14, 11:23 AM
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Quote Quote by vrmuth View Post
when water reaches to touch the heavy materials which are so hot what happens ? water becomes vapour but the water in the upper layer will cool it right ? can you please throw some light on it
That depends on how hot the vapor is, how much vapor and how much water there is and so on, all these heat balance things. No simple answer to that.
FactChecker
#12
May27-14, 06:11 PM
P: 288
Quote Quote by vrmuth View Post
Hi i have this question in my mind for very long time ,what stops water on earth from going further down and down and reach the center of the earth ? i want to know the laws of physics that makes this possible .
I think there are fewer passages for water to go down than you imagine. High pressure in the deep rocks is bound to force them together and close cracks. Many of the remaining cracks will eventually be filled by minerals from the water. The water that can still go down may be stopped at a trap, like under your sink or forces from below (steam, etc.) may stop it from descending further. Any water that still makes it low enough will be turned into steam.
vrmuth
#13
Jun11-14, 07:39 AM
P: 78
ok , can you guys give me any links for pictures that illustrates this in details ?


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