On Our Planet

The greatest force on our planet is polar, but not magnetic.
It's soft and yielding.  In small quantities it seems almost pathetic,
But in great torrents, it carves canyons and cliffs and great natural steeples.
Goldilocks would love it.  Too much or too little is lethal.
It's clear.  It's barely there.  It seems you can hardly see it,
But it seems like it's everywhere and you always seem to need it.