Ancient aliens

"Ancient civilizations generated many innovations that are difficult to explain, such as the remarkable mathematical accuracy of the pyramids of Giza, the man-made fertile soil of the Amazon known as terra preta, and massive stone monuments too heavy to move in Peru and Lebanon, among other places. Given that modern science cannot explain these mysterious phenomena, one theory holds that ancient aliens were responsible for them. This volume examines the credibility of various paranormal hypotheses, giving readers the opportunity to explore the greatest puzzles of antiquity"--Provided by the publisher.