I must wonder where, exactly, is the line where I start and something else begins. You could wonder for any two physical objects, any group of things on any plane, but the form of the question that interests me is: Where do I end, and the organisms inside me begin? More importantly, what do you have to have to be considered truly alive?

It is not a ridiculous thing to assume that the first organisms with multiple cells were originally two symbiotic single-celled organisms that over years of symbiosis became one. That seems to mean that we are just combinations of little cells that combined into a bigger clump of organic matter.

Most animals are ecosystems, as well as being part of larger ones. They are home to thousands upon thousands of beings that develop in tune perfectly with the organism in which they reside. They are, oftentimes, critical to the animal's existance, sometimes needed for the animal to stay alive. But who is to say, that when the animal dies, that it is really even dead? The heart stops, the brain ceases to function as it used to, but life can still thrive, albeit different life. Living things can thrive off of a corpse, there is no meaningful difference between alive and dead any more than between stages of life where a human changes.

I wonder, then, are we just little cells in the big organism of the Earth? Most of our dear planet, of course, is not alive, is not organic matter, but I wonder, what does that mean? We have no evidence of anything really being alive, we don't know why things stay in existence. In the end, we know very little, and so why not imagine that Earth is alive, in a sense, that we are little bacteria scurrying about on its surface? Who knows what concious thought can dwell in? Who knows if it can reside in stone and steel and molten lava. We have no idea. We assume far too much, as much as any religion, it seems sometimes.

It's a structure rooted in a fabricated ground that we don't understand.

Any thoughts of organisms as communities and vice-versa would be appreciated.

I think you are trying to take a scientific liklihood and extend it into a philosophical no-man's land.

Whatever the opposite of "Reductio ad absurdum" is ... I think that that is where you're heading.

Back up a bit and apply some critical thinking.

But to answer your question ... likely all organisms, with the possible exception of the most extreme primiives are communities.

But having acknowledged that ... so what. ;-)

We are what we are.

"And so why not imagine that Earth is alive, in a sense, that we are little bacteria scurrying about on its surface? "

I do. Why not imagine further, in both directions?

(Unrelated to the above statement)
I have said this already in another topic, but are you aware that you have literally DIED many times? The atoms that made you at one point in time, e.g. when you were a baby, can in theory be found and reformed into a previous version of you while the current you still exists.