How did the new continents across the atlantic ocean come to be called america?

When the large new map, approximately 8 feet by 4 feet, was unveiled by Waldseemüller, it had the large title “AMERICA” across what is now present day Brazil. Waldseemüller used Vespucci’s travelogues as a reference for his drawing and so his map had South America as the only part of this new western hemisphere. When North America was later added, the mapmakers of the time retained the original name. In 1538, The famous geographer Gerard Mercator chose to name the entire north and south parts of America as one large “America” for the entire western hemisphere

Because the discoveries were some of the oldest human remains.