or did this not become a subject of writing until the modern age?
This is going to answer only a small portion of your question, but I can tell you that literary scholars view the Romantic Movement as making definite contributions to Modern European/American understandings of nature as beautiful. Romanticism rose to its peak alongside the industrial revolution and acted as a sort of artistic backlash to a cultural emphasis on capitalism and urbanization. It frequently invoked nostalgic images of agricultural lifestyle (called pastorals) and emphasized the beauty and power of nature over manmade artifice. It also gave us the idea of the sublime, a sense of terror or wonder inspired by a realization of how small you are in light of nature’s majesty.
While romanticism developed in England as an offshoot of sentimentalism, with the classic examples of romantic works being very English-centric, the movement resonated with, and was appropriated by, pretty much every North American and European culture. There’s a huge amount of romantic literature, art, and music from all over the world during the late 18th and early 19th century. I don’t think there’s any question that romanticism is at least partially responsible for giving us a general cultural understanding of nature as containing a lot of beauty, and I also think that this understanding is a direct consequence of the modernizing process.
To put it in more clear terms, while people almost certainly saw nature as beautiful before romanticism/modernity, I don’t think they thought of it in the same was as we do now. The industrial revolution started a long process that gradually removed the influence of nature from people’s day–to-day lives and consequently it became ripe for artistic pastiche and nostalgia. It’s easy to fantasize about living in a log cabin in the woods when you’re commuting to work in a traffic jam every day, and that distinctly modern circumstance gives such fantasies a power that simply wasn’t present for a lot of pre-19th century people who were stastically more likely to perform agricultural labour and live outside of cities. That’s my personal understanding as a scholar of late 18th century literature anyways.
However, romanticism is a little bit outside my field so for better information I recommend this text by Michael Ferber, which comes from the excellent “short introduction” series. It also has a surprisingly comprehensive and well cited Wikipedia page.
Also, I can’t emphasize enough that Romanticism is a highly Euro-centric explanation for why we consider nature beautiful. For example, the 17th century Japanese poetry of Matsuo Basho demonstrates an incredibly powerful belief in the beauty of the natural world almost 200 years before romanticism (or Japan's own process of Modernization) came to be. I assume that every culture has its own unique relationship to artistic depictions of nature and I'm sure you could find many examples that have “always” found it beautiful.
hi! here are a couple of related posts; check them out for previous responses
How has our attitude towards "Nature" varied with time and place?
(I believe the question was also posted in /r/AskAnthropology)
I'm not certain exactly what you mean by the modern age but the current trend of art praising the beauty of nature was started by two men, William Wordsworth and Samuel Taylor Coleridge when they published Lyrical Ballads in 1798. This kicked off the Romantic era of art, and heavily influenced artists in other genres (Beethoven's Pastoral Symphony is one famous early response). If you consider the modern age, at least in terms of art, to have started in the 20th century with Stravinski's Rite of Spring and the painting of Picasso and Dali this becomes more muddled. Depending on who you ask modern art is a completely new and unique age, or the latest offshoot of Romanticism. This is particularly difficult when genre hopping, as modern writers have a great deal in common with Romantic poets and novelists, in music and painting things are a bit more open to interpretation.
To answer your question specifically though the glorification of natural beauty has been a constant theme in all forms of art to their earliest antecedents. The earliest paintings are pastoral scenes, cave paintings of animals in nature. The earliest literature, core mythology contains pastoral elements. The garden of Eden is an idyllic agrarian utopia, the Epic of Gilgamesh describes it's hero as a corrupt urbanite who travels out in nature, meets a man of the wild and through this friendship becomes a better man and better ruler.
William Wordsworth's Preface to Lyrical Ballads, explaining why he and Coleridge chose rustic subjects: http://www.bartleby.com/39/36.html
The Second Chapter of Genesis, The Garden of Eden: http://www.biblegateway.com/passage/?search=Genesis%202&version=NIV
The Epic of Gilgamesh: http://www.ancienttexts.org/library/mesopotamian/gilgamesh/
Upper Paleolithic Cave Painting: http://en.wikipedia.org/wiki/File:AltamiraBison.jpg
The Harvesters by Pieter Bruegel the Elder, 1565: http://www.metmuseum.org/toah/works-of-art/19.164
Pastoral Symphony, Beethoven, 1808: http://www.youtube.com/watch?v=iQGm0H9l9I4
These are just a few basic examples, as I said natural beauty, rustic themes and the Pastoral in all genres is a constant theme of art throughout human history.
