Quick answer

Most international internet traffic travels through fiber-optic cables on the seafloor, not satellites. The network now consists of hundreds of cable systems spanning well over a million kilometers, with repeaters, landing stations, repair ships, private ownership, and geopolitical oversight behind the simple experience of loading a page from another continent.

When you send an email from London to New York, it almost certainly travels through a cable on the floor of the Atlantic Ocean. Not a satellite. Not the air. A physical cable, roughly the diameter of a garden hose, buried under several kilometers of seawater, carrying light pulses at speeds approaching the physical limit of fiber optics.

There are now more than 500 submarine cable systems in service globally, totaling well over 1 million kilometers in length. They carry the overwhelming majority of international internet traffic. Satellites matter for remote coverage, broadcast, backup links, and mobility, but the high-capacity internet between continents mostly runs through glass fibers on the ocean floor.

What the cables actually are

A modern undersea cable is a marvel of engineering that looks deceptively simple from the outside. The outer layer is polyethylene. Inside that is a steel wire strand for strength, then another polyethylene layer, then copper for power (the cable's amplifiers need electricity), then more protective layers, and finally at the very center: optical fibers, each one thinner than a human hair.

Each fiber carries data as pulses of light. A single modern cable might contain eight fiber pairs, and each pair can carry terabits of data per second. The current generation of cables can move over 350 terabits per second — the equivalent of streaming millions of HD videos simultaneously.

The sharks

There's a persistent story that sharks bite undersea cables. This is true but wildly overstated. Shark bites account for a tiny fraction of cable faults. The real culprits, in order of frequency: fishing trawlers dragging anchors across the seafloor, ships' anchors, and undersea landslides. In deep water — below about 1,000 meters — cables are rarely damaged because human activity doesn't reach there.

Who owns them

The cables are owned by a mix of telecom consortiums and, increasingly, technology companies. Google, Meta, Amazon, and Microsoft now either own or have substantial stakes in a significant portion of the world's undersea cable capacity. Google alone is involved in over 30 cable systems.

This shift happened because the hyperscalers discovered that buying or building capacity directly was cheaper than leasing it from traditional carriers. It also gave them more control over latency and routing — important when you're operating global services that need consistent response times.

What happens when one breaks

Cable faults happen roughly 200 times per year globally. When a cable breaks, traffic reroutes automatically through other cables — the internet was designed for this kind of redundancy. Users rarely notice.

Repairing a cable break requires a specialized ship that grapples the cable from the seafloor, brings it up, splices in a new section, and lowers it back. A deep-water repair can take weeks and cost millions of dollars. There are only about 60 cable repair ships operating worldwide, and they're in constant demand.

The geopolitical layer

Undersea cables have become increasingly strategic infrastructure. Several countries have raised concerns about cables landing in specific locations or being owned by companies with ties to particular governments. The US has blocked or added conditions to several cable projects on national security grounds. In 2022, the UK, US, and Australia announced a joint cable project partly as a counter to Chinese investment in Pacific cable infrastructure.

The physical internet is, it turns out, deeply political. The cables that route your data are not neutral infrastructure — they're assets that governments, intelligence agencies, and corporations actively compete to influence.

The next time a video loads instantly from the other side of the world, there's a cable on an ocean floor somewhere doing the work.

Sources

For another physical layer of global systems, see Critical Minerals and Resource Politics.