the investigation one that scientists hope might explain the trenches formation world the next step was clear investigators needed to understand whether there was a connection between the trench and the East Pacific re shield the mold the breakthrough came from the unlikeliest of sources little during the Cold War the US built a vast network of underground seismometers to pick up atomic bomb testing around the world inadvertently the seismometers also detected naturally-occurring earthquakes ok when geologists plotted these on a map a pattern emerged one the earthquakes were clustered along the ocean's riches and trenches was a discovery the transformed our understanding of the earth for geologists realize the friction that causes earthquakes comes from movements that must be occurring deep beneath the ridges and trenches on with this great investment and seismology that became possible to us ocate very precisely where earthquakes have occurred that it was these things the precise location the DEP and the motion really gave the outlines a plate tectonics on it was the birth have an extraordinary new theory on the solid layer a rock the crust on which the land and ocean sits is broken up into a series a vast slabs the geologists call tectonic plates on it's these plates that are moving grinding past each other and triggering earthquakes the underwater ridges and trenches said on the boundaries between tectonic plates the East Pacific Ridge and the Marianas Trench lie on opposite edges the Pacific Plate world journey to discover what form the Marianas Trench is accumulating additional evidence the Trieste dive to the bottom of the trench and confirmed that it is the deepest point on the planet sonar maps then revealed the East Pacific Ocean Ridge running parallel to the trench to solve the mystery in the Marianas Trench investigators needed to find out exactly what was happening at the East Pacific Ridge that meant exploring these vast mountains 18,000 feet underwater ok little the pieces have the Marianas Trench puzzle are falling into place with the knowledge that it lies on the western edge at the Pacific tectonic plate like on the opposite side of the plate lies the East Pacific Ocean Ridge part of an enormous change them underwater mountain ranges that bring the globe to create the largest geological feature on earth like scientists have a hunch that this colossal range might help explain how the trench was born the I'll they found a major clue halfway around the globe where the ridge passed beneath the middle of the Atlantic Ocean welcome during the Cold War the US Navy developed a new technique to spot soviet submarines they scanned the seas with the tool called mad a magnetic anomaly detector which could pinpoint steel halls lurking in the deep the but they stumbled across something else the running parallel on either side of the ridge they found strange stripes