a billion years ago, No. America started to split up, creating a 3000km crack — right under the land where I grew up near Duluth around Lake Superior.   But then the process stopped and no ocean emerged through this crack.   but the rift created between 1-2 million cubic kilometres of basalt, which is what you see driving around Duluth.   wild

This story in Nature is amazing.  science is cool.

http://www.nature.com/news/geology-north-america-s-broken-heart-1.14281