For many years, scientists and archaeologists thought that the first Homo sapiens arrived in the Americas roughly 13,000 years ago, through an "ice-free corridor" within a large ice sheet largely blocking the route from Asia into the Americas. But after scientists discovered human remains in Mexico dating to roughly 13,500 years ago, scientists began revising their theories about how the first humans arrived. Jon Erlandson of the University of Oregon believes that these first humans paddled boats down the coastline of the Pacific, following the kelp forests along the Pacific Coast and rivers through the interior of the continent, all the way into South America.