What if humans weren't the first civilization on Earth?
Is it possible that modern humans aren't the first civilization on Earth? This is the insanely interesting question probed by "The Silurian Hypothesis", a new paper authored by Gavin A. Schmidt and Adam Frank, two NASA scientists. As they point out, if an industrialized civilization existed in the deep past, it's not clear there'd be easily recognizable traces of it. Our geologic record doesn't go back any further than the Quaternary period of about 2.6 million years ago.