Science Channel's most watched series reveals Earth as it's never been seen before. Illuminating views captured by more than 4,000 orbiting satellites, `What on Earth?' investigates mysteries from strange geological occurrences to weird man-made structures. Every day, the eyes in the sky uncover new mysterious phenomena, and some defy easy explanation. To search for answers, the series combines modern imaging technology with analysis from military and intelligence professionals as well as leading scientists.
Satellite images could explain desert ruins rumoured to be an entrance to an underworld and a city-sized chunk of ice suddenly disappears in Antarctica. (S3, ep 1)
A giant carving of a strange creature suddenly appears in the Australian Outback and mysterious bright green lights illuminate the seas around Thailand. (S3, ep 2)
Strange black holes appear near Egypt's ancient pyramids and a mysterious red swarm invades a beach in India. (S3, ep3)
A bright pink lake could point to a strange, undiscovered new species. When a young boy disappears in a sand dune, satellite images help with the investigation. (S3, ep 4)
Investigators find a new clue about the missing Malaysia Airlines flight that disappeared in 2014, and an astronaut spots something strange in the Sahara Desert. (S3, ep 5)
An ominous shadow engulfs the Pacific Ocean and scientists have trouble explaining a strange lake that's shaped like a perfect circle. (S3, ep 6)
A dagger sealed in King Tut's tomb for over 3,000 years is made of a possibly extraterrestrial metal. A huge swastika is found in the desert near Roswell. (S3, ep 7)
A heavily armoured force takes over one of Syria's most ancient archaeological sites, prompting fears that its relics are being stolen. (S3, ep 8)
A giant swastika appears in a forest in Germany. A strange pattern is etched into the desert near the famous Nazca lines, but archaeologists don't know who put it there. (S3, ep 9)
Satellite images reveal how El Chapo escaped from a high-security prison in Mexico and a giant black stain appears in a war-torn area of Iraq. (S3, ep 10)
A giant letter Z is carved into a Mexican hillside, evoking the mark of a legendary outlaw. A strange sighting in Germany points to secrets from the Cold War. (S3, ep 11)
An area of the US-Mexico border becomes an international mystery and ancient rock carvings in a remote mountain range depict unearthly beings. (S3, ep 12)
An amateur archaeologist finds strange symbols scratched into the Kazakhstan desert and a lake in the Brazilian rain forest turns bright pink. (S3, ep 13)
When terrorists kidnap more than 200 schoolgirls in northern Nigeria, rescuers use satellites to track them down. (S3, ep 14)
New evidence could lead to the discovery of an unknown ancient civilization in the Amazon rainforest and an unidentified submarine is spotted in a North Korean shipyard. (S3, ep 15)
A giant chasm opens in Siberia, dubbed a gateway to the underworld. Meanwhile, an entire island mysteriously vanishes without a trace.
A bright green swirling spiral appears in the seas of the Persian Gulf and a massive complex suddenly appears in Myanmar. (S3, ep 17)
Strange images from a remote and empty desert could explain the mysterious mummies found there and an apocalyptic sandstorm swallows the Middle East. (S3, ep 18)
A young boy makes international headlines when he uses satellite images to discover lost cities of the Maya and trees in China seem to be spelling out a sinister message. (S3, ep 19)
The myth of Merlin is associated with an arrangement of stones in northern France. Satellite images might finally explain this ancient riddle. (S3, ep 20)