There are over 7 billion people living on the earth right now. Tens of millions are born and die each year. Every single one of us leaves signs of our existence in the air, water, soil -- even space.

Looked at another way, if one were to measure our planet's age as a single 24-hour day, the first human civilizations would appear less than a second before midnight. The geological time scale ...

The first human migrations out of Africa are thought ... are considered part of the same vast civilization, the Indus Valley Civilization, which thrived from 2600 to 1900 BCE.

The development of civilization brought a new standard of living to human societies, but it also brought problems such as warfare, environmental degradation and disparity of wealth. Looking at the ...