Nasa's Unexplained Files
Earth's Secret Aliens
Season 3 Episode 20 of 24
Geologists begin to ask questions about 'alien' deposits found on the Earth's surface - and the answer could shed light on the cause of history's greatest extinction event
Nasa's Unexplained Files airs on Discovery Science at 4:00 PM, Tuesday 24 December. (Subtitles.)
Topics
Education ➝ Science ➝ Factual Topics
Unexplained ➝ Mysteries