How deep is the ocean and what’s at 3,900 metres?

More than 80% of the bottom of the sea is unmapped and unexplored.

The submersible vessel named Titan(OceanGate Expeditions/PA)

Rescue teams are still racing against time to find the missing 22ft submersible, named Titan, which was on a mission to dive near wreckage of the Titanic in the North Atlantic Ocean.

The vessel, with five people on board, lost communication with tour operators off the coast of Newfoundland, Canada, on Sunday.