No wonder Darién is rugged terrain: it’s geologically new. It was formed in the Pliocene less than 3 million years ago. It’s pretty much the newest land in all the Americas. Previously North America and South America were not joined together; once they split from Pangea in the Jurassic (c. 200 MYA), there was open water between them called the Central American Seaway. It closed only when the Caribbean Plate overrode the Pacific Plate. The effects were: 1) volcanoes along the convergent plate boundary; 2) uplift of the ocean floor because of two plates piled up one on top of the other; 3) sediment getting trapped by the uplifted undersea ridge and building up until it connected together the volcanic islands in that arc, forming the continuous land bridge of Panama.
It’s been there for only less than three million years, while it had been open ocean for about 200 million years, to get some perspective. Once it closed up, it made an enormous difference in global sea currents and climate, now that the Atlantic and Pacific could no longer flow freely together. It rerouted currents in the Atlantic to form the Gulf Stream, on which the warmth of Western Europe depends. Bio exchange that now began with North American species drastically altered South America’s ecology which had been isolated for 200 million years; many extinctions. The closure of the seaway is considered one of the major geological events of the Cenozoic.
It’s going to open up again, as the North American and South American Plates continue to drift independently of each other. Better make that drive while you still can! You got a few million years left.
