From what I can see, there aren't any concerts this weekend or next. This gives us time to explore some topics and go a little deeper with them.
First up, the major triad that opens Wagner's Das Rheingold. The horns stretch this chord over a slow arpeggio. This major arpeggio represents the beginning of all nature motifs.
Nature is the basis from which The Ring Cycle arises and ultimately returns to. Wagner paints this picture for us clearly as the nature theme creeps out of the darkness.
As the strings enter, their theme is still based on the major triad. This is the definitive version of the nature motif.
When the strings begin to move at double speed, we have the motif of The River Rhine. The river flows with more and more energy until the Rhinemaidens enter with their short lived celebration of nature.
Later in the story, the Earth Goddess, Erda, arises to warn Wotan of the god's doom. Her theme is the slow brass arpeggio but this time it is a minor triad. Erda is a new manifestation of nature and has a slightly different motif.
As Erda cautions Wotan the motif inverts and becomes a downward minor arpeggio representing the gods decaying back into nature. We can hear this occur in the orchestra at the 3:50 mark in the clip below.
Wagner has taken two basic musical forms, the major and minor triad, and out them he creates an entire world that rises and declines.
There are several other nature motifs in The Ring Cycle like those of The Rhinegold, The World Ash Tree, and The Forest Murmurs but we can't get that in depth yet.