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Can Helium disappear? As we know Helium is lighter than air, so basically Helium fly off from Earth. Is it possible that in the future we will run out Helium?

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Geo-economics note: responses from different countries are likely to be vastly different in terms of what is seen as "waste" of helium. The only reasonably cheap and large-scale source of the stuff comes as an intentionally captured byproduct in certain natural gas extraction sites. The US, for instance, has at least one enormous helium-rich natural gas supply that has been carefully mined for many years to get the helium. But other countries have no such resources and so helium will appear much more precious there. –  Chris White Sep 26 '13 at 4:21

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Yes, helium can leave the Earth, and yes, we will run out of helium, but because of different reasons. When you buy a helium balloon and its contents get released, this helium goes into the atmosphere. It isn't gone, and it could in principle be purified out of normal air. However, the total amount of helium in the atmosphere is so small it is technologically not feasible to do that. At some point the technology might be developed, but it is unlikely to be economical.

On top of that, helium does also escape from the atmosphere. Since it is so light, it drifts naturally to the upper layers, and there it is easily torn away by the solar wind. However, this process will occur on geological timescales, unless we were to waste so much helium that the total atmospheric content changed appreciably. Keep in mind, though, that even if the helium doesn't leave Earth it is lost to us once it's diluted in the atmosphere.

So: yes, we will run out, and yes, it will make everything awful. And yes, you should cringe when you see helium balloons at a childrens' party.

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Can we produce Helium? –  Gil Sep 26 '13 at 12:21
    
I've only had an introductory course on the subject, but wouldn't nuclear fusion (once the technology is economically viable) give us a way to restock on helium? –  Wouter Sep 26 '13 at 12:23
    
@EmilioPisanty +1, I had no idea this was even possible. I just realized something. If we produced enough CO2, at some point it would displace all the oxygen and nitrogen from the atmosphere. Is this possible? –  dj_mummy Sep 26 '13 at 13:03
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@dj_mummy No. CO$_2$ concentrations are in the parts per million. If that rises from 300 ppm (past) through 400 ppm (current) to, say, 1%, global warming will kill all of us well before we get drowned in it. –  Emilio Pisanty Sep 26 '13 at 13:08
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I think you underestimate fusion power and/or the worlds hunger for energy. 10^20 J/year is already close to an order of magnitude too low. 10^7 * 10^11 = 10^18, which is about 0.5% of our 2008 worldwide consumption. Given that 1. consumption increases each year, 2. hydrogen can be obtained from water with just electricity (electrolysis), and 3. a sustained fusion reaction is essentially free energy, I think the Helium supply problem will be solved, post-ignition. Yes, I consider myself an optimist, why do you ask? –  Patrick M Sep 26 '13 at 14:06

It would probably hang around just around the atmosphere, because even though being lighter than air, it still has mass.

Also, helium is created on earth from radioactive decay in elements like uranium, because a helium nucleus is a deadly alpha particle. As long as we can make alpha particles, we can make helium.

Helium is also created in stars during nuclear fusion.

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I'm going o uptick this for mentioning the replenishment, but the creation of new helium in stars is of little interest to the question of the terrestrial supply. –  dmckee Sep 26 '13 at 1:31

Since Helium is so light it can actually escape into outer space. See here. Most of the helium we use comes from radioactive particles decaying underground. Yes, we can run out, and yes, it will make everything awful.

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Short answer: yes.

Given the value of helium, we should be making every effort to conserve it. When we run out of fossil hydrocarbon fuels we can find alternative sources of energy, but when helium is gone, it's gone.

I cringe every time I see a kid's birthday party with helium filled balloons.

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If helium is so scarce and valuable, and party balloons so cheap, why aren't the researchers buying up all the helium from the party suppliers? –  congusbongus Sep 26 '13 at 0:38
    
@congusbongus popularmechanics.com/science/health/med-tech/… –  Andy Sep 26 '13 at 1:02
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Just wait until you realize the amount a helium lost in dumping a super-pressure balloon. Or in the quench of a large superconducting magnet. –  dmckee Sep 26 '13 at 1:30
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As we know Helium is lighter than air, so basically Helium fly off from Earth

Just because Helium is lighter than air doesn't mean that it flies off Earth. At http://en.wikipedia.org/wiki/Atmosphere_of_Earth you can read that

[In the Homosphere] ... the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.

This has the consequence that Helium is equally likely to be found at the surface of the earth as at the top of the homosphere (up to ~100km). The ratio of Helium here is 5.24 ppmv (from Wikipedia page).

The fact that a helium balloon rises is due to the fact that the helium is kept together. If you would just release a lot of helium into air, it would spread out and mix, and not rise indefinitely as one might expect.

In the heterosphere (>~100km), however, the pressure is low enough to allow the gases to stratify by molecular weight (related to the Mean free path, see the Wikipedia page). So if you would release helium above 100km, it would rise above other gases, even without a balloon, which is why helium and hydrogen tend to be found further out in the hetereosphere.

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