The best explanation for how humans populated the earth is a. they migrated from asia to other continents over the last two million years. b. they migrated mostly over land from africa c. over the last eighty thousand years. they developed varied human species in different places over millions of years. d. they traveled by boat from africa to other continents over the last forty thousand years.

What is the main difference between primary and secondary sources? a. primary sources are historical documents, and secondary sources are modern-day documents. b. primary sources are derived from museums and archives, and secondary sources are created by history students and academics. c. primary sources are found in ancient places with a rich history, and secondary sources are found in historical journals and blogs. d. primary sources are created during a particular historical era, and secondary sources are created by studying primary sources.