I haven't heard of this being called the Gaia Theory, but I have thought a lot about it and agree with it.
An organism is just a system of particles that sustains itself and has defined boundaries. Thus, the Earth.
By the way, the philosopher David Chalmers proposed that any collection of particles (like the brain) can have a consciousness, and that thus even the earth can have a consciousness.
SO go hug yer tree!
<span style=\'color:green\'>For the love of a tree, go out on a limb.</span>