How do undersea cables carry the internet?

Hundreds of submarine cables stretch across the world's oceans, with a combined length of well over a million kilometres, and they carry the vast majority of data travelling between continents. Inside each cable are hair-thin strands of glass fibre that carry data encoded as pulses of laser light. In deep water, a cable can be about as thick as a garden hose, while near the shore it is armoured with steel to protect it from anchors and fishing gear. Devices called repeaters, spaced along the cable, boost the light signal so it can cross thousands of kilometres. The first transatlantic telegraph cable was completed in 1858, and the first transatlantic fibre-optic cable, TAT-8, began service in 1988.