Deep in the ocean is where things get really interesting. Descend below one kilometre to the bathypelagic zone and the creatures take a weird turn. Descend even further to 11 kilometres – the bottom of the Mariana Trench – and the marine life becomes completely surreal.

The Mariana Trench is the unexplored world, the seemingly never-ending abyss, and oceanographers have debated much about it in modern times: What sounds echo up from down there? What lives under those rock formations? With so many questions left unanswered about this crescent-shaped scar that measures more than 2,500 kilometres long and 69 kilometres wide, this “wound of the Earth’s crust” may just hold the secrets to our underworld, and life’s very beginning.

2000px-pelagiczone-svgInto the Deep

The trench was first discovered in 1875 by the British ship H.M.S. Challenger, which managed to record a depth of eight kilometres using a weighted sounding rope. This was followed in 1951 by another British vessel, H.M.S. Challenger II, which used an echo-sounder to remeasure the trench – resulting in a recorded depth of nearly 11 kilometres. At extreme depths, the bottom of the Mariana Trench is hidden by total darkness – kilometres out of reach of any light.

To shed some of their own light on what exactly was hiding in the depths of the trench, in 1960 Jacques Piccard and Navy Lt. Don Walsh took on the dangerous task of exploring the trench in a U.S. Navy submersible, a bathyscaphe called the Trieste. After a five-hour-long descent, the pair spent just 20 minutes at the bottom. Incredibly, at nine kilometres deep one of the windows of the submersible cracked – but turning back was not an option and the pair continued on their mission. Unfortunately, when at the bottom, no photographs were taken due to clouds of silt stirred up by their landing. In an environment so harsh, with pressure so high, the pair were amazed to find – illuminated by their submersible’s floodlight – a creature moving that vaguely resembled the look of a flatfish. Finally, that pressing question of whether life could exist so deep was answered.

For decades, the Mariana Trench was left alone, and it wasn’t until 2012 when film director James Cameron began preparations to explore the deep. A submersible was designed especially to reach the deepest point of the trench. Named, Deepsea Challenger, the craft was equipped with scientific sampling equipment and 3D cameras. It was more technologically advanced than its predecessor, the Trieste, featuring over 180 other on-board systems, including life support, LED lighting, thrusters, and a sophisticated underwater communications system.

Although it was the most advanced submersible ever built, the mission was not without risk. There was no knowing for sure whether the vessel would be able to handle the extreme pressure – and not simply crumble in on itself. After a number of successful and unsuccessful trial dives, Cameron finally reached the bottom of the trench – Challenger Deep – clocking a depth of 10,908 metres. What he witnessed reminded him of images that he saw of the moon landing, barren and lifeless. During the three hours he spent at the bottom, Cameron did encounter types of jellyfish and shrimp-like critters – but not the huge deep-sea predators he had hoped for. However, on reviewing the footage captured by his vessel, scientists did make out camouflaged sea cucumbers on the seabed, and the fact that they had adapted to use camouflage to prevent being eaten by predators suggested that there could be larger creatures patrolling the deep.

Life in the Abyss

During Cameron’s dive, 68 new species were discovered. Among the incredible animals that have adapted to life at such extreme depth: the telescope octopus, a transparent cephalopod with solid rotating eyes; and the well-known anglerfish, which can grow up to one metre long and uses an elongated dorsal spine that uses bioluminescence to attract its prey.

Later, in 2014, the Schmidt Ocean Institute collaborated with a team of scientists aboard the oceanographic research vessel RV Falkor and conducted a comprehensive study of the trench. At a depth of over 8,000 metres, an unseen species of snailfish was discovered, along with amphipods that were discovered just under 11 kilometres deep.

Scientists aboard the RV Falkor discovered “the deepest living fish” – an unknown type of snailfish – at a depth of 8,143 metres (via YouTube)

Each new trip brings new findings of marine creatures and occurrences. Recently, a microphone was sent down to the bottom of the trench to discover what such a depth sounded like. Kept there for three weeks, the microphone picked up sounds from mainly earthquakes and boats, but most interestingly it also recorded what they believed to be whale sounds.

With so much still to discover about the depths of our oceans, this incredible trench – formed over millennia by the geologic process of subduction – is key to understanding how life can survive against such impossible odds.