Geologists usually trace the history of their science back to the Geological Revolution, ca. 1800, when it was recognized that the Earth is very much more ancient than indicated in the biblical account. Geologists are thus accustomed to think that geology is a much younger science than modern astronomy and physics, which date back to the Copernican Revolution, ca. 1540–1690. We argue that this is only because geologists are neglecting a major advance in understanding the Earth that occurred a century before that. We argue that geologists should recognize the Portuguese Voyages of Discovery, later joined by the Spanish, as a major episode in the history of what would now be called geology. This revolutionary advance was driven by technological changes, yielded a cornucopia of discoveries, was marked by great excitement, and led to major changes in worldview and society. The Voyages of Discovery have been intensely studied by historians of geography, but not by historians of geology. Therefore we are at pains to show that they should be taken as part of the history of geology, as well as that of geography, for they led to central geological discoveries. These discoveries included the shape of coastlines whose match later demonstrated continental drift, the fact that there is more ocean than land, the arrangement of planetary climate zones, and the patterns of winds and the geomagnetic field. This new historical viewpoint sees geology as a science at least as old and worthy of respect as physics and astronomy, and this is an important consideration as a scientific understanding of the Earth becomes critical to the flourishing of the biosphere and of humanity.