Ask most people how a message gets from London to Sydney and they'll point at the sky — satellites, surely. They'd be almost entirely wrong. About 99% of all intercontinental internet traffic travels not through space but through fibre-optic cables lying on the ocean floor — a hidden web of glass threads crossing the deepest parts of the sea to link the continents.
There are roughly 600 submarine cable systems in service or planned, stretching some 1.5 million kilometres — enough cable to wrap around the Earth about 37 times. Each is barely thicker than a garden hose, packed with hair-thin fibres that carry data as pulses of light. A single modern cable can move thousands of terabits per second — enough to stream millions of videos at once.
Satellites do exist up there, and constellations like Starlink genuinely help — for ships, aircraft, remote villages and disaster zones. But they complement the cables rather than replace them. By capacity, satellites account for a tiny sliver: an old US regulator's figure put them at just 0.37% of the country's international capacity, and newer analysis still lands cables above 99%. Cables win on capacity, cost and latency, and it isn't close.
For comparison, the seabed backbone by the numbers:
- Share of intercontinental traffic: ~99% by cable
- Satellites' share: well under 1%
- Cable systems: ~600, spanning ~1.5 million km
- Faults per year: ~200 — mostly ships' anchors and fishing gear, not sharks
One honest caveat: the 99% figure is about traffic that crosses an ocean. A great deal of everyday internet use never leaves your region — that data travels overland and never touches a cable. But the moment your click needs another continent, it almost certainly dives into the sea to get there.
The next time someone talks about data living "in the cloud," remember the cloud has a floor — and it's lying on the bottom of the ocean.