Scientists have determined that our moon once had an atmosphere about three or four billion years ago, which formed when volcanic eruptions spewed gas too quickly for it to leak into space. Researchers studied impact basins filled with volcanic basalt that are on the surface of the moon to come to this conclusion.

Scientists think that the basalt plains, which are known as maria, were caused from magma bursting from the moon’s surface and causing lava flows. Thanks to the Apollo missions, we know these lava flows were made up of carbon monoxide and other gas components, as well as sulfur and some of the building blocks of water.

Our moon has no atmosphere currently, as it doesn’t have a strong enough magnetic field to sustain one, nor does it have enough mass to have one. But the new research indicates that it did at least briefly have an atmosphere thanks to these volcanic events.

“A new study shows that an atmosphere was produced around the ancient Moon, 3 to 4 billion years ago, when intense volcanic eruptions spewed gases above the surface faster than they could escape to space,” reads a USRA statement. “The study, supported by NASA’s Solar System Exploration Research Virtual Institute, was published in Earth and Planetary Science Letters. When one looks up at the Moon, dark surfaces of volcanic basalt can be easily seen to fill large impact basins. Those seas of basalt, known as maria, erupted while the interior of the Moon was still hot and generating magmatic plumes that sometimes breached the lunar surface and flowed for hundreds of kilometers. Analyses of Apollo samples indicate those magmas carried gas components, such as carbon monoxide, the ingredients for water, sulfur, and other volatile species.”