Is this fiction or non-fiction?

This would normally be classified as fiction, as stream of consciousness depicts a continuous flow of thoughts. So, an internal dialogue, if that makes sense.

As I understand it you want to write a story of the Earth as a first person narrative from the Earth's point of view. ("Stream of consciousness" means something different from that, but we will leave that to another question).

Fiction or non- fiction is going to depend on if you introduce fictional elements. On the face of it, since the Earth does not have consciousness, you would seem to have introduced a fictional element to start with. You could make it less fictional by, for example, telling the story in the passive voice without implying thoughts or feelings.

Then a new kind of animal appeared on my surface called Mankind. They began to dig into my crust to extract minerals. They took their waste and dumped it in my rivers. Some other animals vanished, never to return.

You could make it more fictional by giving the Earth personal attributes:

I was horrified at what Mankind was doing to me. How could they cause me such pain, digging into my crust and poisoning my rivers? My continents writhe in agony.

Even more fictional elements could be introduced, like underground spirits or continents talking to each other.

For a matter of style like this fiction or not is going to be a matter of opinion.