For the first time in 30 years, the gaping hole in the ozone layer above Antarctica is showing signs of healing.

Every year since it was discovered in 1985, scientists have watched the hole grow bigger from one Antarctic spring to the next, eventually covering 10.9 million square miles in 2015. Now researchers are noting an encouraging trend. Though the hole still exists and reached a record size last year, it is forming at a slower rate, said a report in the journal Science.

Thanks to human actions to curb the use of ozone-destroying chlorofluorocarbons, or CFCs, the hole has started growing later in the spring, the study's authors said, and they can foresee a time, around the middle of the century, when it's gone. "We are starting to see signs of improvement over Antarctica," said Paul Newman, an atmospheric scientist at NASA's Goddard Space Flight Center in Maryland who monitors the hole but was not involved in the study.

Earth wears the ozone layer like a thick blanket. The invisible gas blocks the majority of the sun's harmful ultraviolet radiation. Without that shield, life as we know it would not be possible.

The hole in the ozone layer comes and goes over the course of each year. The conditions for creating it begin in late August, and it reaches its maximum size in October.

Study leader Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology, and her colleagues examined data going back to 1970 to see whether ozone levels had improved. Although they didn't see that much difference from one October to the next, they could see that between 2000 and 2014, ozone levels during September had improved.

Then came 2015. The size of the ozone hole in October broke a record, even though levels of CFC byproducts in the atmosphere were still falling. "Could it be that the volcanoes are holding back the ozone from recovering?" Solomon said.

When the researchers considered the effects of the sulfur particles, they could see that the answer was yes. In fact, the Calbuco eruption in Chile increased the size of the ozone hole in September by 2.7 million square miles. Without the volcano, the researchers said the hole would have continued to heal. "We took action, and here we are 30 years later," Solomon said, "seeing that that action has produced the positive result that we hoped for."