Our atmosphere has a lot of gas in it - nitrogen, oxygen, argon, and carbon dioxide, but it hasn't always had these gasses. Is it possible that we may one day not have enough oxygen in our atmosphere to survive on our own planet?
Everything that happens from our magnetic field to space rocks impacting our Earth can have an impact on our atmosphere. As matter from space comes crashing down to Earth, it creates a massive shockwave that displaces a ton of gas into the vacuum of space.
The magnetic field has a lot to do with why we have the atmosphere we have today. Mars, for example, has almost no magnetic activity left, and this is why solar winds have stripped the red planet of most of its atmosphere. Our magnetic field, fortunately, continues to be strong enough to hold solar winds back.
Will we one day not have enough oxygen to support life? - Very possibly, but not for a long time.