Something big is happening to the ozone layer, and it could have huge ramifications for our planet.

In a miraculous turnaround, scientists have found that the massive hole in the ozone layer over Antarctica has started to heal, according to a MIT statement.

The hole had been cited for decades as a major problem for our planet and indicative of of the damage being done by human actions, so such a turnaround is an incredible discovery.

A new study published this past week in the journal Science credits the 1987 Montreal Protocol, an international treaty that phased out chemicals responsible for damaging the ozone layer, with helping to reverse the problem. Since 2000, the ozone hole has shrunk by more than 1.5 million square miles since 2000, which is about half of the size of the contiguous United States.

While eliminating chemicals like chlorine certainly helped, scientists also acknowledge that other factors were likely at play. For example, the eruption of the Andean volcano Calbuco likely resulted in a widening of the hole.

But if nothing had been done about the chemicals, it’s possible we would have lost two-thirds of the ozone layer by 2065 worldwide. Instead, if things keep going as they are, the ozone hole could heal over in a matter of decades.

“We can now be confident that the things we’ve done have put the planet on a path to heal,” said lead author Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT. “Which is pretty good for us, isn’t it? Aren’t we amazing humans, that we did something that created a situation that we decided collectively, as a world, ‘Let’s get rid of these molecules’? We got rid of them, and now we’re seeing the planet respond.”

Scientists first discovered the ozone hole in the 1950s.

Scientists have measured ozone in October typically because that is when the ozone level is at its lowest. However, researchers in this study believe September may actually be the better time, which is when the latest measurements were taken.

“I think people, myself included, had been too focused on October, because that’s when the ozone hole is enormous, in its full glory,” Solomon says. “But October is also subject to the slings and arrows of other things that vary, like slight changes in meteorology. September is a better time to look because chlorine chemistry is firmly in control of the rate at which the hole forms at that time of year. That point hasn’t really been made strongly in the past.”