Throughout the world, ancient objects have been found that leave archaeologists at a loss. Could these impossible artifacts suggest that advanced--and perhaps even extraterrestrial--civilizations existed on Earth thousands of years before our own?

Amy Shira Teitel, Ana Gruia, David Childress, Deepak Shimkhada, Dominic Steavu, Giorgio A. Tsoukalos, Jason Martell, Jeff Williams, Julie Lee, Michio Kaku, Nova Spivack, Richard 'Ric' Rader, Robert Schoch, William Henry