BANGKOK: When Dr Deo Florence Onda found himself more than 10,000m below the surface, in the third deepest trench on the planet, he was on the lookout for mysteries hidden in the darkness.

The Emden Deep, part of the Philippine Trench, is one of Earth’s final frontiers, an unexplored section of one of the oldest seabeds in the world. Until just a couple of months ago, no human had ever been there.