The ozone layer is a region of Earth's atmosphere, about 10 to 30 miles above the surface, where a special form of oxygen called ozone is concentrated. Ozone molecules act like an invisible shield, absorbing most of the sun's harmful ultraviolet rays before they reach the ground.

Without this protective layer, the sun's radiation would make life on Earth's surface much more dangerous. It would damage the DNA in living cells, cause serious sunburns, harm crops, and kill tiny organisms in the ocean that form the foundation of the food chain.

In the 1980s, scientists discovered that certain chemicals used in spray cans and refrigerators were thinning the ozone layer, particularly over Antarctica. This discovery led to the Montreal Protocol, an international agreement to phase out these dangerous chemicals. It stands as one of science's great success stories: nations worked together based on scientific evidence, and the ozone layer has been slowly healing ever since.

The ozone layer is distinct from ground-level ozone, which is a pollutant that can make breathing difficult. High in the atmosphere, ozone protects us. Near the ground, it's harmful. Context matters a lot.