Geologically, South America has more in common with Africa than with North America. It has to do with the breakup of the super-continent of Pangea into Laurasia and Gondwanaland at the end of the Permian period.
Sometime during the middle or end of the Jurrasic period both of these large continents (remnants of the former Pangea) broke along a north-south line. North America started drifting west from Laurasia, and South America separated from Gondwanaland and also drifted west. The ithsmus started to form during the Jurrasic as a common leading edge shared by the two drifting continents, but it was only about 5.7 million years ago that a complete land bridge sealed off the connection between the Atlantic and the Pacific oceans. An interesting sidebar to this exciting drama is that the newly formed ithsmus opened a land bridge which allowed an invasion of species from the north, and set off a round of extinctions South America.
In my opinion (probably doesn't account for much) North America and South America share a common westward techtonic drift, but that's about all. To call them part of the same continent is really a stretch. They are two completely separate tectonic plates.
I just thought I'd throw that out there. I knew you would all find it tremendously fascinating.
BTW, it is this westward drift that is ultimately responsible for all the great riding country in the mountain west. (See, there is my tie-in to motorcycling.)
Regards,
Cody
