Is it possible that another civilization existed before us? That's the question posited by the Silurian Hypothesis.

Famed anthropologist Margaret Mead was once asked, “What was the first sign of human civilization?” You might think she would have mentioned prehistoric cave drawings, the discovery of fire, or ...

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.