In what eras were the most significant geographical discoveries made? why?

The New Time became such an era. That is, from the end of the 15th century to the beginning of the 20th century. In the 21st century, in terms of geography, something fundamentally new was not discovered, and in the Middle Ages there were no permanent contacts by sea between continents. In modern times, the Europeans discovered America and their ships reached first India and then Japan, circumnavigating Africa, which was not the case before (the Arabs sailed only to Mozambique).

And even in the New Time, Australia, the islands of Oceania and Siberia were discovered.