Madagascar is a large island about ~400km off the coast of Africa. It was settled by Austronesians who embarked about 2000 years ago launching from the island of Borneo (of Malaysia), not by Africans, although Bantu speakers do appear to have colonized the somewhat closer Comoros Islands.
Cape Verde, the Azores, the Falkland Islands--the world is not lacking for places that were never colonized until the Age of Exploration despite being remarkably close to continents. Actually colonizing a place is more difficult than getting a few people together on a boat and hoping you hit land (read up on how the Austronesians actually colonized the remote islands that they found). When crossing such massive bodies of water as the Atlantic or Pacific Ocean, you need stores of rations if you want to live to make it to the other side, and it's not clear that a Paleolithic society could have produced a sufficient food surplus to provision the voyage.
Also, the possible discovery of Newfoundland based on the Grand Banks doesn't predate Columbus by all that much. The clearest indications of its existence postdate Cabot's exploration in 1497. Claimants of precedence generally still date to the 1400s--usually making reference to around 1470. Archaeological evidence of any pre-Columbian, post-Viking contact with Newfoundland has not been forthcoming.
Cape Verde, the Azores, the Falkland Islands--the world is not lacking for places that were never colonized until the Age of Exploration despite being remarkably close to continents. Actually colonizing a place is more difficult than getting a few people together on a boat and hoping you hit land (read up on how the Austronesians actually colonized the remote islands that they found). When crossing such massive bodies of water as the Atlantic or Pacific Ocean, you need stores of rations if you want to live to make it to the other side, and it's not clear that a Paleolithic society could have produced a sufficient food surplus to provision the voyage.
Also, the possible discovery of Newfoundland based on the Grand Banks doesn't predate Columbus by all that much. The clearest indications of its existence postdate Cabot's exploration in 1497. Claimants of precedence generally still date to the 1400s--usually making reference to around 1470. Archaeological evidence of any pre-Columbian, post-Viking contact with Newfoundland has not been forthcoming.