Could natural disasters really be the work of extraterrestrial forces? In 2011, after a 30-foot tsunami ravaged Tohoku, Japan, the local media reported more than 1,000 UFO sightings over the inundated shoreline. Did otherworldly beings that descended from the sky have anything to do with the abrupt disappearance of the Mayans? Are Grey Aliens real? Many have claimed to have been visited and even abducted by them. Is NASA sharing all that it knows about the universe, or are they protecting us from the truth? 'Ancient Aliens: Series 4' continues to examine 25 thousand years of the most credible alien evidence here on Earth.