For most of the agrarian era, the four world zones operated independently of each other with little or no knowledge of what was going on in the other zones. The world, in effect, was divided into four unconnected regions, none of which was really interested in the others. With the improved transportation and communication technologies developed 500 years ago, humans acquired the means for connecting these formerly independent zones. After 1492, for example, the Americas and Afro-Eurasia were put in regular contact, and the Columbian Exchange saw the transfer of people, ideas, animals, plants, and diseases between these two once separate world zones. Exchanges like these fueled social, political, economic, and intellectual innovation. Within a few hundred years, this more fully connected world saw dramatic acceleration in innovation and population growth, which ushered in the Modern Revolution.