The physics of losing Helium from the Earth - question

[GTrax]

Helium is seen to be "lighter" than air only when it is confined in a balloon or similar so as to be able to displace the heavier stuff around it.

Released loose, the atoms seem to mix with the air around very swiftly. I mean about 50 metres in 2 or 3 seconds, and then it seems to hang about steadily getting more dispersed, but still enough to make a vacuum leak detector howl, for maybe 20 minutes. Forgive the very casual approximate descriptions - this was not a real experiment!

There have been recent alleged "concerns" that helium is a non-renewable resource, countered by other accusations that this is hype intended to affect the share price and profits of helium-mining companies. As I understand it, Earth Helium is mostly derived from Radon gas decay.
http://amarillo.com/news/local-news/2010-09-13/helium-prices-jump-curb-debt"
http://www.mnn.com/earth-matters/wilderness-resources/stories/helium-crisis-spreads-around-the-world

So the question(s) ..
What exactly happens to released helium, party balloon or otherwise?
Does it drift up to "float "above the atmosphere, and get blown off into space?
Does it remain a "mixture" with air?

 

[rcgldr]

The main method of atmospheric escape on the Earth is due to a tiny portion of molecules at the fringes of the atmosphere that achieve escape velocity:

http://en.wikipedia.org/wiki/Atmospheric_escape

 

[D H]

So the question(s) ..
What exactly happens to released helium, party balloon or otherwise?
Does it drift up to "float "above the atmosphere, and get blown off into space?
Does it remain a "mixture" with air?

The troposphere is rather well-mixed. Higher layers of the atmosphere are not. The helium in that balloon will be mixed in with the other gases in the troposphere. While the tropopause is an inversion layer, some mixing of the gases in the lower and upper atmosphere still occurs. That helium will cross the tropopause eventually. Once it does, bye-bye (after a while). Above 75-100 miles altitude or so, the upper atmosphere becomes too tenuous to support fluid flow. Diffusion processes dominate in the upper atmosphere. The physics of this diffusion means that migration to the upper reaches of the atmosphere will be biased toward lighter constituents. The very top of the atmosphere, the exosphere, is almost all hydrogen.

 

[GTrax]

My thanks D H.
How we retain any of our atmosphere is, I suppose, closely related. Were it not for the magnetic field deflecting the main solar wind around the earth, I guess much of the atmosphere would be off into space. That there is a retained layer of Hydrogen up there is comforting. It is still with us, not just blown away, and it is even lighter than Helium!