The isthmus is thought to have been finally formed around 3 million years ago (Ma),[2] separating the Atlantic and Pacific Oceans and causing the creation of the Gulf Stream, as first suggested in 1910 by Henry Fairfield Osborn. Osborn based the proposal on the fossil record of mammals in Central America,[3] a conclusion that would provide a foundation for Alfred Wegener when he proposed the theory of continental drift in 1912.[4] Some recent studies[5][6][7] suggest an earlier formation of the isthmus than the recognized age of 3 Ma, potentially stretching as far back as 19 Ma.[8]