Water

[Genghis_Khan]

Not so much skepticism, but a simple science question I've recently thought about.

Is water made on earth, or was there always a finite amount here and we're just using it up? I know things on earth are composed of water, but does anything make water? If no,[and my uneducated guess is no] then what do you think we are going to do? If yes, please share.

[Mageth]

Not so much skepticism, but a simple science question I've recently thought about.

Is water made on earth, or was there always a finite amount here and we're just using it up? I know things on earth are composed of water, but does anything make water? If no,[and my uneducated guess is no] then what do you think we are going to do? If yes, please share.

One hypothesis is that terrestrial water arrived in icy comets a long time ago. Water can be "made" (by combining hydrogen and oxygen as a product or byproduct of a chemical reaction) but I know of no significant -natural- processes on earth that are attributed with having "made" our terrestrial water supply.

The only "things on earth" that are "composed" of water are water and ice. Some other "things" (like us) comprise water (and depend on it) as well as other elements/compounds.

And we're not "using up" water, exactly. We're not reducing the amount of water on earth by any significant percentage. What we are doing is (regionally) depleting the amount of easily "usable" water (e.g., easily obtainable surface and subsurface fresh water) and, in many cases, polluting that water so that it's not usable. The problem with water supply/allocation is particularly significant in some regions, e.g. in large parts of the American West, where increasing population has pushed the usage/allocation of available freshwater sources to the max in some cases. Other regions have plentiful available fresh water, although increasing populations and industrial usage threaten even some of those regions.

[Genghis_Khan]

Nice.

That basically covers what I wanted answered. Thanks Mageth

[Schneibster]

Water is one of the "four ices:" water, ammonia, methane, and carbon dioxide. Each is the simplest possible combination of two of carbon, hydrogen, oxygen, and nitrogen: water is H₂O, ammonia is NH₃, methane is CH₄, and carbon dioxide is CO₂. Nitrogen does not readily combine with either carbon or oxygen, so where those four elements are concerned, these are the combinations that these four elements can make easily.

Now, carbon-12 and oxygen-16 are made, respectively, of three and four helium nuclei; the helium nucleus is particularly stable, which is why radioactive elements eject helium nuclei when they have to get rid of protons to become stable. Physicists call such ejected helium nuclei "alpha particles." The combination of two of them is extremely unstable, with a half-life in the femtoseconds; it immediately dissociates into two alpha particles. But the combination of three or four of them is particularly stable; the reasons for this have to do with details of the operation of the color force that are well beyond the scope of this conversation. However, in addition to all of this, you need to keep in mind that when a star runs out of hydrogen and begins fusing helium, it's going to make a lot of carbon-12 and oxygen-16. Another pathway leads easily to nitrogen-14. So these elements are going to be relatively commonly created in heavy stars that are burning their way toward supernovahood. When they explode, these elements are going to be spread around into the interstellar medium.

We can detect the elements and molecules present in the giant molecular cloud complexes that occur at intervals along the spiral arms of the Milky Way galaxy, using a variety of optical, infrared, and radio spectroscopy, and what we find is plenty of these elements, and plenty of the ices that will easily form when these elements are brought together; as well as more complex molecules, alkanes, alcohols, amines, and so forth. For instance, it is estimated that there is enough ethyl alcohol in the giant molecular cloud complex that forms the middle of Orion's sword, a nebula variously called M42, the Sword Nebula, the Orion Nebula, or NGC1976, to fill ten million martini glasses the size of Earth. Obviously, there is a great deal more water (an order of magnitude or more greater, in fact) than there is alcohol. And there are also copious quantities of methane, ammonia, and carbon dioxide.

If you know M42 well, you'll know that there is a formation of very young stars near its center whose stellar wind is blowing an enormous bubble in the nebula; these stars are called the "Trapezium." So we know that stars are formed in such nebulae. And quite a bit of infrared and radio astronomy in that region has shown us that there are many more stars being born there, right now. In addition, this is by no means a unique circumstance; pretty much all of the other giant molecular cloud complexes we see in the nearby spiral arms are doing much the same thing. You can have a look at the Hubble picture titled, "Pillars of Creation," a shot of a small portion of the Eagle Nebula, M16, NGC6611, in Serpens, which shows another giant molecular cloud complex and associated young stars.

So clearly, new stars are being born in regions where there is quite a bit of this type of material around.

Astrophysicists believe that planetary systems are formed at or near the same time as stars are, out of the "bubble" of material, called a "stellar nebula," that the star is formed from. Thus, a star that has planets is going to have had them formed from material that contains quite a bit of the ices. Keeping in mind that all of this is driven by gravity, and that the specific gravity of the heavier elements, like silicon, iron, and so forth is higher than that of the ices, we can see that rocky planets like Earth, Venus, and Mars are going to wind up with a rocky inside and an icy outside. And in fact, they have wound up just like that.

So that's where Earth's water came from.

The cometary impact theory has some merit as well; when stars first ignite, they seem to give forth a very strong stellar wind for the first few million years of their life. Astrophysicists theorize that this might blow all the ices off the rocky cores of the planets close in to the star. If that is the case, then Earth would have been pretty barren, and most of the water we see around us might have come from comets after the Sun had quieted down; but remember, those comets were formed from the same stellar nebula that all the rest of our Solar System was, and it all came from the earlier supernovae. So it's still where it all came from, it's just a dispute about the exact route it got here via.

OK, so what about "using up" water?

Well, water is heavier than air- most of the time, we'll get to that in a moment- so it flows downhill to the lowest places in Earth's crust. We call the giant puddles that result, "oceans," "seas," and "lakes." The first two are very old puddles; they have been around for most of the lifetime of the Earth, although they have shifted around (or, more properly, the continents have shifted around within them). Now, water is a peculiar substance; it is very nearly a universal solvent. Most simple chemicals will go into solution in water; particularly, salts will do so. And in fact, they have; so the Earth's oceans and seas are salty. But lakes have not been around very long, and they aren't contiguous with the oceans; and both because the easily accessible salts have already dissolved into the ocean, and because lakes are not connected to the ocean, they are generally fresh water.

Now, the sea is heated all the time by the Sun. And when water is heated, it evaporates, turning into water vapor. Remember I said most times water is heavier than air? Well, water vapor is not; in fact, most places on Earth, there is quite a bit of water vapor in the air. You'll be familiar with clouds, and rain, and so forth- suffice it to say that water is continually evaporated from the sea, and from lakes, and forms clouds, which then rain, and flow back into the sea and lakes, and this is a continuous cycle.

We of course cannot drink salt water; in fact, if you try, you will relatively quickly die of it. So the largest portion of the Earth's water is basically unusable for drinking. That means that we are dependent upon lake and river water. We make artificial lakes behind dams to provide water for drinking, and also to control the flow of water in rivers and prevent floods. But in many places, even this is not sufficient to provide enough water for the growing population. You see, it is not in this case a matter of the amount of water, but the rate at which the water rains out of the sky. Thus, not only are our demands for water increasing with our population, but when droughts come, they strain these resources to (and sometimes beyond) their limits.

In other words, there is plenty of water- it's just mostly unusable. And the rate at which usable water is being made is sometimes too slow. To top it all off, we make mistakes like polluting water that we might otherwise use to drink, and damaging the environment in our watersheds, areas where rain falls and trickles down into rivers and lakes that we later obtain drinking water from. And these mistakes cut further into the available supply of clean water for us to drink.

And worst of all, we are currently facing a situation in which the climate is being modified by the gases we create with our industrial activity- "global warming." This will probably have effects in some places that will lead to deserts- areas where rain does not fall, and where rivers and lakes do not exist. It may also lead the oceans to rise, which will contaminate some sources of fresh water with salt, making them unusable. While the details are under political question, they are not under scientific question- the vast majority of climate scientists agree that it is bound to happen, it is merely a question of how long it will take and how bad it will get. We may already be seeing some of the effects in the increases in severity of hurricanes, and in the melting of the Arctic and Antarctic icepacks, although it will be several years at minimum before we have enough data to be completely certain that these effects are due to this problem.

Hopefully this will clear up your understanding of the Earth's water supply, and help you to understand what people are talking about when they discuss it.

[Genghis_Khan]

Wow Schneibster...that could have been an entire school period of discussion. Thanks alot though, very interesting stuff.

You actually made me think of another question when you began to talk about stars,though. You said:

And quite a bit of infrared and radio astronomy in that region has shown us that there are many more stars being born there, right now.

Now when these stars are 'born' how do they spread out? I mean I'm sure this area you're talking about is quite enormous, but the nearest star next to us besides our sun is what? I don't even know how far away. So how do these stars spread out when they squirm out of the birth canal?

[orpheus last chant]

Schneibster, I took the liberty of copying your excellent post over on a Romanian atheist board, because someone has asked the same question (with proper credits). Hope you don't mind.

[Berthold]

In the long run, though, water, or, more exactly, hydrogen, does get lost: Water molecules are split by energetic UV radiation in the high atmosphere, the hydrogen can then escape. The process may play a substantial role in the far future. See, e. g., "The Life and Death of Planet Earth" by Peter D. Ward and Donald Brownlee.

[Worldtraveller]

Now when these stars are 'born' how do they spread out? I mean I'm sure this area you're talking about is quite enormous, but the nearest star next to us besides our sun is what? I don't even know how far away. So how do these stars spread out when they squirm out of the birth canal?
Excellent post, Schneibster.

I'm not sure how to answer this. Stars don't really 'spread out'. What does happen over many millenia, is that stars die, generally in a large explosion (nova or supernova) and since most (upwards of 80% I think) of a stars hydrogen is actually not consumed before it goes boom, that hydrogen is shot out intot he interstellar medium.

Some important things to know about the life cycles of stars. Bigger stars burn out faster (in as few as 3-4 million years for the really big ones) and the smaller stars last longer. So big stars will coelesce, burn hydrogen into some heavier elements, and explode. The remnants of these will coelesce into new stars and the acretion disks of heavier elements will form planets around them.

This is a greatly simplified explanation. For some good summaries, google 'stellar evolution' and main sequence stars, and browse around NASA's website.

Cheers,
Lane

Note: This was all from memory from my college classes in introductory astronomy, so verify the important stuff for yourself. :D

[llanitedave]

Excellent post, Schneibster.

I'm not sure how to answer this. Stars don't really 'spread out'. What does happen over many millenia, is that stars die, generally in a large explosion (nova or supernova) and since most (upwards of 80% I think) of a stars hydrogen is actually not consumed before it goes boom, that hydrogen is shot out intot he interstellar medium.

Some important things to know about the life cycles of stars. Bigger stars burn out faster (in as few as 3-4 million years for the really big ones) and the smaller stars last longer. So big stars will coelesce, burn hydrogen into some heavier elements, and explode. The remnants of these will coelesce into new stars and the acretion disks of heavier elements will form planets around them.

This is a greatly simplified explanation. For some good summaries, google 'stellar evolution' and main sequence stars, and browse around NASA's website.

Cheers,
Lane

Note: This was all from memory from my college classes in introductory astronomy, so verify the important stuff for yourself. :D

Since most stars form in clusters, and the clusters usually dissipate over time(through gravitational influences from the rest of the galaxy), you could certainly say that the stars "spread out". However, I'm not sure if this covers the sense of the original question.

[Schneibster]

Schneibster, I took the liberty of copying your excellent post over on a Romanian atheist board, because someone has asked the same question (with proper credits). Hope you don't mind.That's fine, with credits. :)

[Schneibster]

Wow Schneibster...that could have been an entire school period of discussion. Thanks alot though, very interesting stuff.Glad you found it helpful.

Now when these stars are 'born' how do they spread out? I mean I'm sure this area you're talking about is quite enormous, but the nearest star next to us besides our sun is what? I don't even know how far away. So how do these stars spread out when they squirm out of the birth canal?The nearest star is Proxima Centauri, about 4.3 light years away; a light year is about six trillion (American trillion: 10^15) miles. It's the distance light travels in a year.

The diameter of the Trapezium cluster (yes, it's a cluster, it has about a thousand stars in it, we can only see eight or ten of them because of the gas and dust in the nebula- we see the rest in infrared which can penetrate the nebula) is about the same as the distance between the Sun and Alpha Centauri; that means there are a thousand stars there in the same space as there are two here. Most likely, most of these stars won't have planets; three of the four visible stars are multiples, two doubles and a triple. Astrophysicists believe that most if not all multiple star systems don't have planets; the material that would have made planets is used up by the extra star(s).

It's important to remember that stars live a very long time indeed; our own star, the Sun, is 4.5 billion years old. Stars generally have "proper motions-" the rate that they move relative to other stars- of a few tens of miles per second. Now, this might not seem like much, but when you consider that a year is 31,557,600 seconds, assuming a modest 20 mi/sec, that's 631,152,000 miles in a year. In a thousand years, it's a tenth of a light year; in a million, it's a hundred light years. And a million years is perhaps one ten-thousandth of the lifetime of a star like ours, which we expect to live about ten billion years.

That's how stars get so far apart, even though they are born close together.

Now, where they get their proper motion from, that's another story; there are probably six or ten theories, but we don't have enough information yet to distinguish between them. And these are very mathematically dense theories; they also have to account for the rotation of the stars and of their companions, whether stars in a multiple star system or planets, and if you have not dealt with rotation yet in physics, it is extremely complex. Well beyond anything I'm prepared to discuss here, and quite possibly beyond my ken unless I am strongly motivated. ;)

[Schneibster]

Excellent post, Schneibster. Thanks. :)

What does happen over many millenia, is that stars die, generally in a large explosion (nova or supernova) and since most (upwards of 80% I think) of a stars hydrogen is actually not consumed before it goes boom, that hydrogen is shot out intot he interstellar medium.This only happens to a minority of stars, those over "Chandrasekhar's Limit," about 2.3 times the mass of our Sun. Most stars just burn out; our Sun, for instance, will first become a red giant, frying the inner planets, and then when most of its atmosphere is blown off, a white dwarf which will live many billions of years burning very slowly but very hot. Eventually, it will run out of fuel, and slowly cool down to a cinder; but the majority of it blown away before it settled down to white dwarfdom will first form a so-called "planetary nebula," then later join the interstellar medium. This process is more important than the supernova process in terms of the amount of elements it adds to the medium, but it doesn't make heavy elements because there is not enough spare energy to do that. Only in a supernova is there enough spare energy to make elements beyond iron; fusing to elements beyond iron doesn't produce energy, it uses it up. So a lot of carbon, oxygen, nitrogen, flourine, and so forth get distributed by the red giant->planetary nebula process, but all the heavy stuff gets made in supernovae, which is why there's a fair bit of light elements around, but not much in the way of heavy ones.

An earlier post I made on the "packing fraction" tells about where the energy from fusion comes from, and why it uses up energy to fuse beyond iron. If no one comes up with a link, and there is interest, I'll go hunt it up.

Some important things to know about the life cycles of stars. Bigger stars burn out faster (in as few as 3-4 million years for the really big ones) and the smaller stars last longer. So big stars will coelesce, burn hydrogen into some heavier elements, and explode. The remnants of these will coelesce into new stars and the acretion disks of heavier elements will form planets around them. This is essentially correct, if simplified as you note later. But note also the other process.

In my last post, I forgot to put a link in to information about the Trapezium; y'all will find this interesting, I think: http://www.astropix.com/HTML/B_WINTER/TRAPEZ.HTM

[Genghis_Khan]

Ya, that link is somewhat beyond me, and I should probably start looking this stuff up if I want to know. But youre a pretty nice resource to have around, Schneibster, and I thought of another question. Like it is in that system M42, more specifically the Orion Nebula, when 2 stars are that close to each other, and lets say their total masses were equal, which would orbit which? Anyone?

[Schneibster]

Ya, that link is somewhat beyond me, and I should probably start looking this stuff up if I want to know. But youre a pretty nice resource to have around, Schneibster, and I thought of another question. Like it is in that system M42, more specifically the Orion Nebula, when 2 stars are that close to each other, and lets say their total masses were equal, which would orbit which? Anyone?Hee hee, that's an easy one. Even the Moon and Earth orbit a common center- the center is inside the Earth, but not at the center. The Earth kind of "wobbles."

The Sun does the same thing with each of the planets- all at the same time. But of course the Sun is so much huger than any of the planets that the center is very, very close to the center of the Sun.

Two stars of equal mass that were orbiting each other would actually orbit a common center halfway between them. The ratio of masses is the ratio of the distances of each center of mass to the center of rotation. Hmm, is that right? Or might it be the square of each mass...? Anybody know off the top of their head?

[Genghis_Khan]

They should really tell us this inour 4th grade astronomy classes. I mean the concept of the orbit being a little bit off isn't that hard to comprehend,and it would save us the trouble of re-asking these questions years later [because 4th grade is the last time science class had any remote to-do-ness with astronomy. Least in my neck of the woods].

Just for shits now, what is the point of a lone star, or a set of lone stars. Now I suppose you're going to say it cycles new material into our universe by that repitition of forming from previously blown stars, burning for however long, then dying off [granted this takes millions or billions of years but eh] and shedding their new materials from their deaths [very crude, lay-ish terms but i think you get what Im trying to say]. So with all that in mind even with the death and rebirth cycle, what's their point? Do they expand our universe? Does the amount of matter they expel amount to more than the amount of older material they were formed from?

[Schneibster]

Well, at minimum, if they are large enough to go to the red giant stage, they'll increase the amount of helium when they form a planetary nebula. Of course, if they aren't big enough for that, then they'll just burn down to a cinder, trapping all their elements in their slowly cooling selves. But only a minority of stars are that small, as far as astrophysicists can tell.

Remember as well, that even if there is plenty of hydrogen left around now, at some point it's going to get more scarce- many, many billions of years from now. Most of it in most galaxies will be burnt up. But that's a really long time off. Much longer than the current age of the universe.

[Loren Pechtel]

Ya, that link is somewhat beyond me, and I should probably start looking this stuff up if I want to know. But youre a pretty nice resource to have around, Schneibster, and I thought of another question. Like it is in that system M42, more specifically the Orion Nebula, when 2 stars are that close to each other, and lets say their total masses were equal, which would orbit which? Anyone?

Which would orbit which isn't really a meaningful concept. *ALL* orbits are mutual. They orbit the center of gravity of the system, not each other.

In most cases one object is far more massive than the other and thus the center of gravity is inside the larger object. It wobbles a bit and it looks like the other is going around it. (Note that this is how we are detecting extrasolar planets--looking for the wobble in the star.)

However, when you have two objects of equal mass they will both orbit a point halfway between them.

[llanitedave]

Hee hee, that's an easy one. Even the Moon and Earth orbit a common center- the center is inside the Earth, but not at the center. The Earth kind of "wobbles."

The Sun does the same thing with each of the planets- all at the same time. But of course the Sun is so much huger than any of the planets that the center is very, very close to the center of the Sun.

Two stars of equal mass that were orbiting each other would actually orbit a common center halfway between them. The ratio of masses is the ratio of the distances of each center of mass to the center of rotation. Hmm, is that right? Or might it be the square of each mass...? Anybody know off the top of their head?

This is going to be a guess, because I don't have time to look it up, but I *think* that the relative distances are linear, not exponential.

If I get a chance, I'll work it out later...