The lecturer discusses reasons why we haven't detected any of the possible 12.5 civilizations deduced to be residing in the Milky Way Galaxy based on the Drake equation. The space between possible civilizations is discussed, as is the...

Through a video, this tutorial enables the student to identify the four major Early River Valley civilizations. [10:45]

When humans began farming, new, more complex ways of living were possible. This video looks at the factors that led to the rise in agriculture. [2:37]