Most people imagine the internet as an invisible cloud of wireless data. But 99 percent of international traffic travels through garden-hose-sized cables lying at the bottom of the ocean.
Today, more than 500 active submarine cables crisscross the globe. They transmit data via rapid pulses of light through glass fibers no thicker than a human hair. To survive the pressurized environment of the ocean floor, these fragile fibers are wrapped in layers of copper, steel wire, and a thick outer sheath of polyethylene and tar.
Because this infrastructure rests on the seabed, it faces incredibly low-tech threats. Cyberattacks rarely cause physical internet outages. Instead, the vast majority of cable faults happen when commercial fishing trawlers drag nets along the bottom, or ships accidentally drop anchors. Underwater earthquakes and submarine landslides also routinely snap the lines.
When a cable breaks, repairing the internet requires a grueling maritime operation. Specialized ships sail to the fault, drop a mechanical grapple thousands of feet down, drag the broken ends to the surface, and manually splice the glass fibers back together on deck.
Almost every streamed video, cleared financial transaction, and instant message ultimately relies on these physical threads of glass resting in the mud.