Some people know about the Permian mass extinction, which left only about four percent of species alive. That’s also the one that finished off the trilobites, which is a bummer because they seem pretty cool.
This isn’t really the Vale of Arryn, but it plays it on TV.
At times, I feel like I have a better handle on the history of Westeros and Essos (which I obviously need to follow the Game of Thrones storyline), than the history of our actually-existing world. It never even occurred to me, though, to wonder if the Narrow Sea is a geologically-recent development, resulting from the separation of the two continents about 25 million years ago.
A group of (mostly) Stanford geologists, however, have been wondering about that, and their ideas are collecting in the form of a geological history of Westeros at their blog, Generation Anthropocene.