It was the void that changed public perception of the environment forever—a growing spot so scary, it mobilized a generation of scientists and brought the world together to battle a threat to our atmosphere. But 30 years after its discovery, the ozone hole just doesn’t have the horror-story connotations it once did. How did the conversation change—and how bad is the ozone hole today?

To understand, you have to go back about 250 years. Scientists have been trying to study the invisible since the beginning of science, but the first real understanding of Earth's atmosphere came during the 1700s. In 1776, Antoine Lavoisier proved that oxygen was a chemical element, and it took its place as number eight on the periodic table. The scientific revolution that spurred on discoveries like Lavoisier’s also led to experiments with electricity, which produced to a stinky revelation: Passing electricity through oxygen produced a strange, slightly pungent smell.

In the 1830s, Christian Friedrich Schönbein coined the term “ozone” for the odor, riffing off the Greek word ozein, which means “to smell.” Eventually, ozone was discovered to be a gas made from three oxygen atoms. Scientists began to speculate that it was a critical component of the atmosphere and even that it was able to absorb the sun’s rays.

A pair of French scientists named Charles Fabry and Henri Buisson used an interferometer to make the most accurate measurements ever of ozone in the atmosphere in 1913. They discovered that ozone collects in a layer in the stratosphere, roughly 12 to 18 miles above the surface, and absorbs ultraviolet light.

Because it blocks some radiation from reaching Earth's surface, ozone provides critical protection from the sun's scorching rays. If there were no ozone in the atmosphere, writes NASA, “the Sun's intense UV rays would sterilize the Earth's surface.” Over the years, scientists learned that the layer is extremely thin, that it varies over the course of days and seasons and that it has different concentrations over different areas.

Even as researchers began to study ozone levels over time, they started to think about whether it was capable of being depleted. By the 1970s, they were asking how emissions from things like supersonic aircraft and the space shuttle, which emitted exhaust directly into the stratosphere, might affect the gases at that altitude.

But it turned out that contrails weren’t the ozone layer’s worst enemy—the real danger was contained in things like bottles of hairspray and cans of shaving cream. In 1974, a landmark paper showed that chlorofluorocarbons (CFCs) used in spray bottles destroy atmospheric ozone. The discovery earned Paul Crutzen, Mario Molina and F. Sherwood Rowland a Nobel Prize, and all eyes turned to the invisible layer surrounding Earth.

But what they found shocked even scientists who were convinced that CFCs deplete ozone. Richard Farman, an atmospheric scientist who had been collecting data in Antarctica annually for decades, thought his instruments were broken when they began to show drastic drops in ozone over the continent. They weren’t: The ozone layer had been damaged more than scientists could have imagined before Farman discovered the hole.

As word of the ozone hole leaked through the media, it became nothing short of a worldwide sensation. Scientists scrambled to understand the chemical processes behind the hole as the public expressed fear for scientists’ wellbeing at the South Pole, assuming that while studying the hole they would be exposed to UV rays that could render them blind and horrifically sunburned.

Rumors of blind sheep—the increased radiation was thought to cause cataracts—and increased skin cancer stoked public fears. “It’s like AIDS from the sky,” a terrified environmentalist told Newsweek’s staff. Fueled in part by fears of the ozone hole worsening, 24 nations signed the Montreal Protocol limiting the use of CFCs in 1987.

These days, scientists understand a lot more about the ozone hole. They know that it’s a seasonal phenomenon that forms during Antarctica’s spring, when weather heats up and reactions between CFCs and ozone increase. As weather cools during Antarctic winter, the hole gradually recovers until next year. And the Antarctic ozone hole isn’t alone. A “mini-hole” was spotted over Tibet in 2003, and in 2005 scientists confirmed thinning over the Arctic so drastic it could be considered a hole.

Each year during ozone hole season, scientists from around the world track the depletion of the ozone above Antarctica using balloons, satellites and computer models. They have found that the ozone hole is actually getting smaller: Scientists estimate that if the Montreal Protocol had never been implemented, the hole would have grown by 40 percent by 2013. Instead, the hole is expected to completely heal by 2050.

Since the hole opens and closes and is subject to annual variances, air flow patterns and other atmospheric dynamics, it can be hard to keep in the public consciousness.

Bryan Johnson is a research chemist at the National Oceanic and Atmospheric Administration who helps monitor the ozone hole from year to year. He says public concern about the environment has shifted away from the hole to the ways in which carbon dioxide affects the environment. “There are three phases to atmospheric concerns,” he says. “First there was acid rain. Then it was the ozone hole. Now it’s greenhouse gases like CO2.”

It makes sense that as CFCs phase out of the atmosphere—a process that can take 50 to 100 years—concerns about their environmental impacts do, too. But there’s a downside to the hole’s lower profile: The success story could make the public more complacent about other atmospheric emergencies, like climate change.

It was the fear about ozone depletion that mobilized one of the biggest environmental protection victories in recent memory. But while it’s easy to see why blind sheep are bad, gradual changes like those associated with CO2 emissions are harder to quantify (and fear). Also, the public may assume that since the issue of the ozone hole was “fixed” so quickly, it will be just as easy to address the much more complex, slow-moving problem of climate change.

Still, researchers like Johnson see the world’s mobilization around the ozone hole as a beacon of hope in a sometimes bleak climate for science. “The ozone hole is getting better, and it will get better,” says Johnson. It’s not every day a scientific horror story has a happy ending.