# atmosphere mixing **URL:** \ **Category:** Factual Questions\ **Created:** [January 14, 2004, 8:25pm UTC](https://boards.straightdope.com/t/atmosphere-mixing/224442 "2004-01-14T20:25:10Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![zimaane](https://avatars.discourse-cdn.com/v4/letter/z/a3d4f5/32.png) [@zimaane](https://boards.straightdope.com/u/zimaane)\ **Post date:** [January 14, 2004, 8:25pm UTC](https://boards.straightdope.com/t/atmosphere-mixing/224442/1 "2004-01-14T20:25:10Z")
The Earth’s atmosphere is made up of different elements with different atomic weights. So why don’t the heavier elements and compounds like CO2 sink down to the ground and lighter ones like He float to the top? ---
**Author:** ![Jake4](https://avatars.discourse-cdn.com/v4/letter/j/bc8723/32.png) [@Jake4](https://boards.straightdope.com/u/Jake4)\ **Post date:** [January 14, 2004, 8:40pm UTC](https://boards.straightdope.com/t/atmosphere-mixing/224442/2 "2004-01-14T20:40:10Z")
Who’s saying they don’t? I don’t think there’s much He in the atmosphere - it diffuses into space. I know that this happens with hydrogen. ---
**Author:** ![herman\_and\_bill](https://avatars.discourse-cdn.com/v4/letter/h/f1d935/32.png) [@herman\_and\_bill](https://boards.straightdope.com/u/herman_and_bill)\ **Post date:** [January 14, 2004, 10:01pm UTC](https://boards.straightdope.com/t/atmosphere-mixing/224442/3 "2004-01-14T22:01:05Z")
There is lots of wind, this keeps things pretty much stirred up. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [January 14, 2004, 10:49pm UTC](https://boards.straightdope.com/t/atmosphere-mixing/224442/4 "2004-01-14T22:49:58Z")
One of the characteristics of gases is that they expand to fill the available space. So if you put different gases together, they all expand to fill the space evenly. Each gas molecule is moving independently all the time, ensuring the mixing continues no matter what happens.