To reach you, these words were encoded into signals of light moving about 125,000 miles per second through fiber-optic cables. These lines, splayed out across mountains and oceans, are made of hair-thin glass 30 times more transparent than the purest water. The technology was made possible in part by a team from Corning Incorporated. In 1970 they patented a type of cable that could transmit large amounts of information long distances, building on decades of work by other researchers.

Assuming you’re reading this on a smartphone, you also owe a debt to Steve Jobs, who in 2006 asked Corning to make a very thin, strong screen for his new product, the iPhone. The result, Gorilla Glass, now dominates the market for mobile devices: Phones made with the fifth generation of this product can be dropped onto a rough surface from a height of five feet (selfie height) and survive 80 percent of the time.

That’s just the start. Without glass, the world would be unrecognizable. It’s in the eyeglasses on your face, the lightbulbs in your room, and the windows that let you see outside. But despite its ubiquity, there’s still some debate within the research community about how to define “glass.” Some tend to emphasize its solid qualities, others its liquidity. Unanswered questions abound, like what makes one type of glass stronger than another, or why certain mixtures produce their unique optical or structural properties. Add to this the nearly infinite varieties of glass—one database lists over 350,000 types of currently known glass, though in principle the number of mixtures is limitless—and you get a surprisingly large and active field of research that regularly produces astounding new products. Glass has shaped the world more than any other substance, and in many sneaky ways, it’s the defining material of the human era.

“We’ve been making glass for thousands of years, and we still don’t have a good idea of what it is,” says Mathieu Bauchy, a glass expert and materials researcher at UCLA. Most glasses are made by heating and then quickly cooling a mixture of ingredients. In the case of flat glass, which makes up windows, that mixture may include sand (silicon dioxide), lime, and soda. Silicon provides the transparency, calcium provides the strength, and soda reduces the melting point. The swift cooling process doesn’t allow for atoms to form a regular pattern, explains Steve Martin, a glass scientist at Iowa State University.

That helps explain why glass is neither a crystalline solid nor a liquid, but rather an atomically disordered (or amorphous) solid. The atoms within want to reassume a crystal structure, but typically cannot because they are essentially frozen in place. You might have heard that cathedral windows flow over long periods of time, hence why some are thicker at the bottom. That’s false: Such windows were made that way, due to a manufacturing technique that involved spinning molten glass that created uneven patches. But glass does move; it just does so very slowly. A study published last year in the Journal of the American Ceramic Society estimated that room-temperature cathedral glass would take over 1 billion years to flow a single nanometer.

Though natural volcanic glasses like obsidian were fashioned into tools early in human history, glass was probably first manufactured in Mesopotamia more than 4,000 years ago. Likely, it was developed as an offshoot of ceramic-glaze production. The technique soon spread to ancient Egypt, and the first glass objects consisted of beads, amulets, and rods, often colored with added minerals to look like other materials, says Karol Wight, the executive director at the Corning Museum of Glass.

By early in the second millennium B.C., craftsmen began making small vessels like vases. Archaeologists have unearthed cuneiform tablets that spell out the recipe for such materials, but these were written in cryptic language meant to conceal trade secrets, Wight adds.

Glass had already become a serious business by the dawn of the Roman empire. The writer Petronius recounts the tale of a craftsman presenting Emperor Tiberius with a piece of allegedly unbreakable glass. Tiberius asked the craftsman, “Does anyone else know how to blow glass like this?” No, the craftsman replied, thinking he’d made it big. Without warning, Tiberius had the man beheaded. Although Tiberius’s motives remain mysterious, one can imagine such an invention would’ve disrupted Rome’s important glass industry, the first of its kind.

The first big innovation came in the first century B.C., when glassblowing was invented around Jerusalem. Soon the Romans figured out how to make glass relatively clear, and the first glass windows appeared. This was an important shift; previously the material was valued primarily for its color and ornamental properties. Instead of looking at glass, people could now look through it. Within a couple centuries, Romans began producing glass at an industrial scale, and it eventually spread throughout Eurasia.

At this time, the science wasn’t well understood, and glass retained a magical air. For example, the Romans created a fourth-century goblet known as the Lycurgus cup, which appears jade green when lit from the front but blood red when backlit. Research shows that its incredible properties are due to the presence of silver and gold nanoparticles, which change color depending on the observer’s location.

During medieval times, the secrets of glassmaking were kept alive in pockets of Europe and the Arab world. By the High Middle Ages, Europeans were producing stained glass. These magnificent paintings-on-glass, in churches in Western Europe, played a huge role in teaching the mostly illiterate masses church catechism, Wight says. No wonder, then, that they’re referred to as the poor man’s Bible.

Though windows had been around since Roman times, they remained expensive and hard to come by. But that began to change after the building of the Crystal Palace for the 1851 Great Exhibition, a massive structure completed in London containing nearly 1 million square feet of glass. (That’s more than four times the glazed area of the United Nations headquarters in New York, erected a century later.) The Crystal Palace showed people the power and beauty of windows, and had an important influence on architecture and consumer demand down the road, says Alan McLenaghan, the CEO of SageGlass, a company that makes tinted windows and other products. The Crystal Palace burned to the ground in 1936, but windows became much more affordable some years later, when the British glass company Pilkington invented the float-glass technique, a simple way of creating flat planes of glass by floating them atop molten tin.

Long before windows become commonplace, unknown inventors in northern Italy created the first spectacles at the end of the 13th century. The invention helped spread literacy and paved the way for more advanced lenses, which would enable humans to see unfathomable things. Nearby, by the 1400s, Venetians began perfecting the process of making cristallo, a very clear glass, borrowing techniques developed in the Middle East and Asia Minor. One recipe involved melting carefully selected quartz pebbles with purified ashes from salt-loving plants, which, unknown at the time, supplied the right ratio of silica, manganese, and sodium. Secrecy was a matter of life and death; glassmakers, though they enjoyed a high social status, faced execution if they left the Venetian Republic. The Venetians dominated the glass market for the next 200 years.

The Venetians also created the first mirrors made of manufactured glass, which would change the world in untold ways. Prior to this, mirrors consisted of polished metal or obsidian, but they were expensive and didn’t reflect nearly as well. The invention paved the way for telescopes and revolutionized art, allowing the Italian painter Filippo Brunelleschi to discover the linear perspective in 1425. They also changed the conception of the self. The writer Ian Mortimer goes so far as to suggest that prior to glass mirrors, which allowed people to see themselves as unique and separate from others, the concept of individual identity didn’t really exist.

Besides reflection, glass allowed for magnification. Around 1590, the father-son team Hans and Zacharias Janssen invented a compound microscope, with lenses at two ends of a tube, producing a nine-power enlargement. A Dutchman, Antony van Leeuwenhoek, made another leap forward. A relatively uneducated apprentice in a dry-goods store, where he counted threads in cloth using magnifying glasses, he developed new ways of polishing and grinding lenses, creating a device that allowed him to magnify images up to 270 times. This allowed him to accidentally discover microorganisms like bacteria and protists, beginning in the 1670s.

Robert Hooke, an English scientist, reconfirmed these findings and improved upon van Leeuwenhoek’s microscope. He made history when he authored Micrographia, the first book about the microscopic world, with beautiful sketches of previously invisible sights, such as the texture of sponges and tiny creatures like fleas (“adorn’d with a curiously polish’d suite of sable Armour, neatly jointed,” he noted). Peering at cork through a microscope, the honeycomb-like structure therein reminded him of monastery cells, leading him to coin the term “cell.” These advances transformed science and led, amongst other things, to germ theory and microbiology.

Elsewhere in the lab, the development of clear glassware and equipment like beakers and pipettes made it possible to measure and mix different materials and subject them to different pressures. These glass tools enabled the development of modern chemistry and medicine, as well as advances such as the steam engine and internal combustion engine.

While some tinkered with microscopes and graduated cylinders, others were searching the stars. Though there’s some debate about who invented the telescope, the first records show up in the Netherlands in 1608. They were made famous a year later by Galileo Galilei, who improved upon the design and began observing the heavens. The next year he observed the moons of Jupiter, and eventually realized that the geocentric view that had held sway since Greek times didn’t make sense. The Catholic Church wasn’t pleased. A 1616 Inquisitorial commission declared heliocentrism to be “foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture.” Damn glass!

Glass’s influence doesn’t show any signs of waning. Looking to the future, researchers hope to make breakthroughs of similar prominence, using glass to bind up nuclear waste, make safer batteries, and fashion biomedical implants. Engineers are also trying to make sophisticated touch screens, self-tinting windows, and truly unbreakable glass.

The next time you find yourself before glass of one sort or another, consider how strange it is that this material, born of Earth and fire, frozen like the rind of ice on a pond, trapped in atomic purgatory, has facilitated so much human activity and progress. Really see it, instead of just looking through: Without it, there are so many truths we could not see.