It’s common knowledge that cell phones and mobile devices have essentially become the norm in the technology world. What many people probably don’t realize is that the networks that provide many of these very same wireless connections rely on cables — fiber optic cables to be exact.

According to a recent piece from the mobile network operator news site RCRwireless.com, there are actually hundreds of thousands of kilometers of bulk fiber optic cables that travel out of sight and mind under the sea to connect countries and continents.

This underwater network of bulk fiber optic cables is responsible for transmitting about 90% of the world’s data. It’s unclear just how much data is sent via these connections daily, but it’s surely at least measured in terabytes. If you don’t know how much a terabyte is, keep in mind that “mega” is a prefix denoting one million. One terabyte is equal to one million megabytes, so a million terabytes would be a whole lot of megabytes. In data communications, this term is typically used in describing the speed of data transfer in megabits per second, the bandwidth of a given system in megahertz.

Fiber optic cable submarine networks have been around for a lot longer than you probably would guess. According to a 2104 Submarine Telecoms Industry Report authored by Terabit Consulting, companies started constructing this infrastructure in the late 1980s. From that time until 2014, it’s estimated that about $57.2 billion has been invested into approximately 1.275 million kilometers of fiber optic cables.

One of the primary reasons fiber optic cables have been successful and a huge part of the industry stems from their durability and overall lifespan.

“The major drivers of transatlantic cables’ longevity have been advancements in upgrade technology,” the Telecoms report states. “Which correspond precisely to the 6,500-kilometer range of transatlantic spans, combined with extremely competitive pricing of both transatlantic capacity and managed bandwidth products, both of which have thus far eliminated any incentive for operators and content providers to opt for building over buying.”

In an effort to, “help safeguard this critical communications infrastructure and promote reliable communications for businesses and consumers,” the Federal Communication Commission passed new regulations in September of 2015. The hope is that the new regulations will create a better outage reporting system to assist regulators in the event of outages.