Two hundred million years ago the earth consisted of a single vast continent Pangea surrounded by a great planetary sea. Continental drift tore apart Pangaea & for millennia the hemispheres were separate evolving almost entirely different suites of plants & animals. Columbus's arrival in the Americas brought together these long-separate worlds. Many historians believe that this collision of ecosystems & cultures-the Columbian Exchange-was the most consequential event in human history since the Neolithic Revolution. & it was the most consequential event in biological history since the extinction of the dinosaurs. Beginning with the world of microbes & moving up the species ladder to mankind Mann rivetingly describes the profound effect this exchanging of species had on the culture of both continents.