hidden deep beneath the waves the western Pacific lies the Marianas Trench the old deepest point all the ocean's little a loony the first step on the journey of what created this mysterious car in the earth's crust and how it continues to mold the planet takes us back to 1872 when a British research vessel HMS challenger set out on the first ever mission to map the ocean floor from us to record history members just assume that beyond a certain level the sea was pretty flat pretty dead fairly lifeless they weren't expecting to find anything very interesting for four years the challenger crisscross the oceans covering 70,000 miles a third of the distance to the moon the crew plumb the depths every 140 miles using a total of 249 miles a rope and hundreds of pounds have led wat it was tedious backbreaking work but at the time it was the only way to measure the depth of the ocean floor when they got to the western Pacific two hundred miles off the island of Guam the crew routinely lowered the rope for measurement but the wait kept on dropping and running it's a big surprise nobody thought the ocean was this day so all the sudden we've got scientists saying why is that on old eventually the weight struck the bottom it four thousand four hundred seventy five fathoms nearly five miles beneath the ocean surface the scientists are we going wow we find something and what does it mean is it a little hole is it a big hole what kinda features it down that there's a whole lotta questions you get when you find this one spectacular reading the challenger expedition mark the birth of modern oceanography and provided the first crew map the ocean floor it showed how the ocean floor gently slopes away from the land and then plummets thousands of feet into vast flat plains but the western Pacific is different it drops of the game into the five-mile deep hole a whole that blew right out of the water the long-held belief that the sea floor was flat and featureless way and it spawned a mystery because nobody could understand how this strange under water feature came about it would be 75 years before any answers emerged it took a revolutionary new technology sonar to push the investigation forward to the next crucial stage world p sonar was first developed in the early nineteen hundreds and then perfected during the nineteen forties to detect submarines lurking d home the system works by pumping sound waves through the water the waves bounce of solid objects and are reflected back to a detector by measuring the time it takes for the sound waves to bounce back scientists realized they could build a remarkably accurate picture of the world beneath the waves the the world's major maybe spend a lot of time and effort developing submarine hunting technology then the hydrography was discovered that you can use this to chop Obama the sea and it's an awful lot cheaper and easier than using large numbers sale