# Is the Earth air-tight, and does that make plastic bags redundant?

Honestly though, is the Earth considered air-tight in the sense that its gases don't escape?

I'm sure every physicist who reads this is going to tear their hairs out, but the extent of my knowledge in this area is that you need to travel a certain speed to break Earth's gravitational pull and that has me wondering how gases could escape.

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What do the plastic bags have to do with your question? If you intended them as a joke, I find it simply distracting. –  Mark Eichenlaub Jan 20 '12 at 1:36

It means that the time scale goes as $\exp{(m/T)}$ for $m$ the mass of the molecule in question and $T$ the temperature. To first order the time scale for losing $\mathrm{O}_2$ is $\approx\exp{(8)}$ times that for losing $\mathrm{H}_2$. –  dmckee Jan 20 '12 at 1:55
...and if the Earth's surface hydrogen was in the form of $\mathrm{H_2}$ gas instead of mostly water it would all have escaped long ago. –  Nathaniel Jan 20 '12 at 10:52