The origins of humanity and why/how people came to populate nearly all the regions of the globe

Discuss the origins of humanity and why/how people came to populate nearly all the regions of the globe by circa 13,000-14,000 years ago. What occurred that led cultures of both the Western and
Eastern Hemispheres to become separated for thousands of years, and how did agriculture change the life-styles practiced in some of the regions in each hemisphere (provide at least ONE example for
both)? Why can we argue that events that occurred in 1492 C.E. significantly altered the history of the world?