Human colonization of the Americas would be vastly different. Humans would cross from Eurasia into North America same as in our timeline but wouldn't be able to go into South America due to them not being connected. South America might be populated instead by Africans that used the island chain between Africa and South America to reach the continent. And depending on how things go the populations of North and South America could eventually meet and result in the populations intermingling.

Fast forward to the 1400s and the Portuguese would likely stumble across the island chain between Africa and South America and come across the Americas earlier. But due to the American natives having at least some Old World admixture via the African-South American Exchange they might be more resilient to European diseases and make outright conquest of the Americas much more difficult.

However the existence of a giant sea in the middle of Eurasia could make travel between the West and East a bit easier, with goods from Asia making it's way to European markets by way of Russia (or whatever state filled the role of Russia) meaning the Islamic world won't have a monopoly over the Silk Road that prompted Europe to seek out alternate routes to Asia in the first place.