Season 4 opens with a Mayan-conspiracy theme.

The Maya created the most sophisticated calendar systems in the ancient world, and according to many scholars their Long Count Calendar will come to an end on December 21, 2012. What does this mean for mankind? Some researchers believe it will usher in the return of Bolon Yokte--a mysterious god associated with creation and war. Could this god actually be an extraterrestrial as some ancient astronaut theorists believe? Other scholars believe the end of the calendar will bring about a series of catastrophic events that may threaten the very existence of mankind. They point to a rare galactic alignment that will coincide with the end of the Mayan calendar as proof of an impending geological catastrophe. If these doomsday prophecies prove to be true, will it mean the end of the world as we know it? Or could it reveal some profound truth about the origins of the human race?

The Grey Alien race of extra-terrestrials has become a pop-culture phenomenon that continues to capture the imagination and attention of governments, citizens and all who have ever uttered the word abduction!

The role of extraterrestrials in world catastrophes is explored.

Researchers probe NASA-related information in the search for proof of alien contact in the recent and ancient past.

The mysteries of the Puma Punku ruins in South America are explored. Investigators tap into forensic evidence and computer tests to study whether aliens may have inhabited this sophisticated complex.

A possible connection between Bigfoot and aliens is examined.

Leonardo da Vinci's paintings and sketches are examined in search of a possible connection to alien technology.

This episode suggests that some alleged alien encounters and UFO sightings may be of beings from Earth's future traveling in time machines, and that these same beings could have posed as ancient aliens in the distant past.

Angkor Wat, Cambodia, is the world's largest ancient religious temple. Within its megalithic ruins, researches have discovered a depiction of a species of dinosaur - a stegosaurus. But how could the ancients have had knowledge of animals that mainstream science says died out millions of years ago? Why are dinosaurs extinct? Did an alien race of beingshug off the dinosaurs to make room for humankind?

For thousands of years, pyramids were the largest structures on Earth. The best known were constructed in Egypt and Central America, but others have been found all around the world, including in China, Africa and Indonesia.

In 1980, three young military men were sent into a UK forest to investigate strange lights. They reportedly encountered a spacecraft of unknown origin.

Egyptian hieroglyphs depict the use of light bulbs in tombs and secret chambers. And batteries may have been discovered among artifacts from Mesopotamia. Did the Ancients understand electricity, and if so, how did they discover this technology?

Why were ancient civilizations around the world so focused on the Orion constellation? While scientists site many earthly connections, researchers suggest this point in the night sky may have been a so-called Stargate.

Was Albert Einstein a genius? Or was he superhuman? Was his genius "of this world", or was it "otherworldly- Is it possible, as Ancient Astronaut theorists believe, of an extraterrestrial connection to the scientific genius of famous historical figures.