A question about "Lord of the rings"?

The Rohirrim, after being told that hobbits actually exist, is basically asking a rhetorical question, "are we living in a legendary story or are we living in the real world?!", and Aragorn wittily replies, "the 'real world', you say? The real world is where legends happen".

So the Rohirrim uses the metaphor "the green earth in daylight" to mean 'the real world' (he is stressing everyday things - grass, sunlight - in contrast to fantastical stories and imaginary creatures). Aragorn then twists this metaphor to make his own point - he says 'the green earth is where legends happen, the green earth is the stuff of legends'.

To forget all the metaphors and look at what the scene is really about: the Rohirrim is accusing Aragorn of believing that he's in a legendary story instead of in the real world, and Aragorn replies to say that, firstly, hobbits are real, and secondly, that legends are based on real things that happened in the real world - the things that are happening now will become the legends of the future.

So the 'green earth in daylight' is just a metaphor for reality. The bits of the scene that you didn't quote make this clear too.

It has nothing to do with the meaning of nature or the importance of the earth. You have to read it in context.

Basically an analogy of if they see themselves as gods or mortals. Rohirrim is asking if they'd rather be mere men or legendary.

Aragorn cleverly responds that Earth itself is a miracle, and ought to be considered a legend for all the honor men have done on it.

The natural world. Green because that's what color most plants are, and in a predindustrial world like Middle Earth, that's what color most of the world is.

It's the natural world, both in the sense that it is the domain of nature, and in the sense that we don't expect uncanny things to happen there.

Aragorn is saying that the natural world is itself a profound thing, only seeming mundane to us because we are used to it.

Mother earth and nature.