Why is that relevant? Would the Grand Canyon be less grand if it was only a couple millennia old?

There is a qualitative difference between a natural experience and a man-made experience. It's not about the age, although natural landscapes are obviously old. It's about experiencing the forces that shaped the landscape, in their original form.

Natural landscapes are valuable because they don't care about people; they make people small again. You can't adapt that to human convenience, and protect it, at the same time.

I think he means the fact that the GW is man-made instead of a natural phenomenon.

Okay, and how is that significant?

In a conversation about whether or not to add man-made touches to natural beauty... you didn't mention modifying natural beauty, but an already man-made thing.

The works of men, and men themselves, are part of nature.

It is nothing short of hubris to believe otherwise. We, like all apex predators before us, will soon become extinct from this planet leaving only fossils in our wake.

Nature encapsulates us - not the other way around.

Sorry but that's ridiculous. Yes, on a philosophical level you can say that, but the word "nature" is defined as excluding anything human-related.

> "The phenomena of the physical world collectively, including plants, animals, the landscape, and other features and products of the earth, as opposed to humans or human creations" - OED

Otherwise there would be no point having that word as it would by synonymous with "everything".

The works of men, however, didn't take 17 million years to develop.

"Would the Grand Canyon be less grand if it was only a couple millennia old?"

Yes.