If you could travel about 15 to 30 kilometres above your head, you would reach a part of the atmosphere that most people never see but depend on every single day. It is called the ozone layer, and without it, life on Earth would be very different. Invisible, fragile, and yet vital, ozone is one of nature’s great shields, quietly protecting plants, animals, and people from the harsh rays of the Sun.
Ozone itself is a simple gas made up of three oxygen atoms. Most oxygen we breathe is made of two atoms, O₂, but when three join together, they form O₃, which is ozone. This small change gives ozone very special properties. While ordinary oxygen keeps us alive, ozone absorbs most of the Sun’s ultraviolet (UV) radiation, the kind of light that can damage skin, cause cancer, and harm the eyes. Without ozone, these rays would scorch the Earth’s surface and make it far harder for living things to survive.
The story of ozone begins naturally. High above the Earth, when sunlight hits oxygen molecules, some split apart and recombine into ozone. This delicate process has gone on for millions of years, creating a protective blanket around the planet. For a long time, humans did not even know it was there. It was only in the early 20th century that scientists began to understand the ozone layer’s role. At first, it was just another interesting discovery about the sky. Nobody imagined it could one day be in danger.
That changed in the second half of the 20th century. In the 1970s, scientists discovered that certain chemicals used by humans—chlorofluorocarbons, or CFCs—were drifting into the atmosphere and destroying ozone. CFCs were found in everyday products like refrigerators, spray cans, and air-conditioners. They seemed safe at ground level, but high above the Earth, sunlight broke them apart and released chlorine atoms. Just one chlorine atom could destroy thousands of ozone molecules. In 1985, researchers studying Antarctica found something shocking: a giant hole had opened in the ozone layer above the South Pole. For the first time, humanity realised that its actions could harm this invisible shield.
The news caused alarm worldwide. If the ozone layer weakened further, more harmful UV rays would reach the Earth, leading to higher rates of skin cancer, damage to crops, and harm to marine life like plankton, which form the base of ocean food chains. The discovery became one of the biggest environmental challenges of the century.
What happened next is often described as a rare success story in environmental protection. In 1987, countries around the world signed the Montreal Protocol, an international treaty that agreed to phase out the use of CFCs and other ozone-destroying chemicals. Factories redesigned products, scientists developed safer alternatives, and governments worked together in a way rarely seen before. Over time, the ozone layer began to recover. The treaty is still active today, and it is credited with preventing millions of cases of skin cancer and protecting ecosystems worldwide.
While high in the stratosphere it protects us, close to the ground ozone can be harmful. At the surface, ozone forms when sunlight reacts with pollution from cars and factories. This ground-level ozone is a major part of smog, which can irritate lungs and cause breathing problems. So ozone is a kind of double character—essential when high up, but dangerous when too close. That makes it even more fascinating and important to study.
Next time you stand outside on a sunny day, take a moment to think about the unseen layer high above, quietly absorbing the Sun’s rays.
The ozone layer is fragile
If the ozone layer were compressed to sea level, it would only be about 3 millimetres thick, yet it protects the entire planet.
Ultraviolet rays come in three types
Ozone absorbs most UV-B and all UV-C radiation, the most harmful kinds, but lets some UV-A reach the surface.
The Antarctic hole appears every spring
Cold stratospheric clouds over Antarctica make ozone loss much worse during September and October each year.
Satellites keep watch
The first satellite measurements of ozone began in 1978, and modern instruments continue to monitor its thickness daily.
Recovery is slow but steady
Thanks to the Montreal Protocol, scientists estimate the ozone layer will return to pre-1980 levels in most parts of the world by mid-century.
Ozone links to climate change
Ozone-depleting chemicals are also greenhouse gases, so phasing them out has reduced global warming as well.
Ground-level ozone damages crops
High concentrations near the surface can reduce yields of important crops like wheat, soybeans, and maize.