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.

But these signs won't last forever. Our buildings will be gone in a few hundred years. Our stone monuments, plastic, styrofoam, twinkies, even evidence of our inevitable nuclear destruction will eventually be gone.

So how can we be sure that we were the first advanced civilization on earth? Well, according to the Silurian Hypothesis: we can't. Let's find out why!