The moon volcanoes would have deposited uranium into the samples collected by Chang’e 5, making it possible for scientists to measure the element’s radioactive decay.

The uranium is found coupled with lead in the rocks, and slowly leaves behind only the latter element over time. Simply put, the greater the ratio of lead to uranium, the older the rock.

As revolutionary as China’s discovery of moon volcanoes might be, it’s not the first time that recent eruptions have been speculated about. In 2014, a Lunar Reconnaissance Orbiter launched by NASA showed dozens of irregular surface features on the moon, suggesting that some volcanic activity has possibly occurred in the not-so-distant past (in the geological sense of time, anyway).