How do atmosphere's remain stable?

[whowhatwhy]

Ok, so I should know better. But after looking at some recent video footage of the space shuttle and, more precisely, the atmosphere surrounding our planet, it got me thinking about how it all works. Space is a (near as hell) vacuum so why don't gasses produced on earth escape into space? Ok, so we have gravity. Is this the only force in action here to prevent the gases moving from an area of high pressure into a low pressure are? How come the force of gravity is just strong enough to hold the gas particles at a perfect balance to create our atmosphere and is it just the mass of our planet that defines it's gravitational influence? Cheers!

[Clanad]

Gravity is the only force holding our atmosphere (scary, no?). Actually, the Earth's atmosphere does escape molecule by molecule at the boundary layer called the exosphere, but not enough to make any difference. Yes, as well, to the amount of gravity being dependent on the mass of the Earth, Mars, apparently at one time, had more of an atmosphere than it does today, but was lost, according to current theory, because it was, over time, "blown away" by solar winds (not actual winds, but charged particles emitted by the Sun). The theory is this happened on Mars but not Earth because Mars doesn't have the magnetic fields to protect it as does Earth, but that's the answer to another question, no?
Another theory is Mars atmosphere, being mainly carbon dioxide may also have been turned into carbonate. It's been mineralized and has been accumulated in the Martian rocks.
Good question!

[whowhatwhy]

Thanks Clanad...had a good think about that and my next question was going to be...'Why / how does gravity exist'...but i did a quick search and found that this chap had already asked that here:

http://www.phy6.org/stargaze/StarFAQ5.htm#q93

buy the reply was really lame, basically no one knows, but it exists and the whole of science counts on it!

Can anyone else come up with a better explanation for gravity than the physics professor in the above response.

Why does any body attract another just because it has mass? I know the process is through gravity...but why?

[Clanad]

Here's the problem as I see it (don't look for an answer to your question, though)... gravity can be described but not explained. The more one employs formulae the more one is describing gravity. Fact is, even at the quantum level (in my opinion) gravity is an unknown as far as causes. It becomes more of a philisophical discussion than one of true explanation that can be measured.
I realize that science has come eons but I also believe (as do some physicists) that we may never know what gravity is, but will have to be satisfied with knowing how it is, if that makes any sense...
Einstein on gravity (interploation) "...Albert Einstein's theory answers every possible question (except the ones regarding behavior at quantum level) including "why?".
He states that gravity is determined by (present whenever there is) a nontrivial (nonzero) spacetime curvature (for empty spacetime (no matter) the field equations for the gravitational field are:Riccie tensor=0).He asserts that in a flat spacetime (as the ones encountered in special relativity and quantum field theory) gravity is absent." I'm certain that helped you, did it not?

[mibn2cweus]

Gravity is perhaps better defined as the effect of matter on space-time rather than as proper force.
Just as space and time flow in a perceived direction/s, so does the apparent attraction of gravity; even anti-matter experiences attraction toward matter.

If you find this confusing just ignore it and look here.

[mibn2cweus]

Found this:

Gravity with a twist

[whowhatwhy]

mibn2cweus thanks for those really interesting links on gravity...the more we know, the more we know that we don't know, I guess. And Clanad, at first I was wondering what you meant by saying

"It becomes more of a philisophical discussion than one of true explanation that can be measured"

But after doing some background reading I see your point. Most frustrating. Does everything in this world have to have some inexplicable 'force' behind it that we are destined never to understand?! I need a bigger brain I think.