We know that the moon once had a lot of volcanic activity. The most common rock on the moon’s surface is basalt, a well-known igneous rock. However, a new study suggests that this volcanic activity might have continued far longer than we previously thought. Researchers analyzing samples collected by China’s Chang’e-5 mission say they were “surprised” and “excited” to find evidence of volcanism as recently as 120 million years ago — well into the age of the dinosaurs on Earth.

For decades, scientists believed volcanic activity on the Moon had ceased billions of years ago. During the Apollo missions of the 1960s and 1970s, astronauts brought back lunar samples that indicated the Moon experienced widespread volcanic activity between 4.4 billion and 2.0 billion years ago. These eruptions were primarily responsible for creating the dark, basaltic plains — known as lunar maria — that are visible from Earth.

Researchers believed that after that, volcanism on the moon slowly petered out. That changed when the Chang’e-5 mission returned to Earth with fresh samples from the lunar surface in 2020.

New volcanic evidence

The Chang’e 5 lunar mission brought back the first samples from the moon since the Apollo program and the Soviet Union’s Luna 24 mission in the 1970s. China also became the first country to bring back rocks from the far side of the moon with its subsequent Chang’e-6 mission.

Researchers from the Institute of Geology and Geophysics at the Chinese Academy of Sciences (IGGCAS) began examining the new samples in search of volcanic evidence. Among the approximately 3,000 tiny glass beads found in the lunar soil, only three stood out. These beads were volcanic, formed from the molten rock that erupted and cooled rapidly, showing distinct chemical compositions and textures.

Now, the challenge was to determine when they were formed.

To determine the age of the glass beads, scientists used uranium-lead dating, a radiometric technique that measures the decay of uranium isotopes into lead. The results were surprising. The volcanic beads were dated to 123 ± 15 million years ago, making them the youngest evidence of volcanic activity on the Moon to date. This finding significantly extends the known timeline of lunar volcanism, which was previously thought to have ended around 2 billion years ago.

This is weirder than you think

The research team behind the study said they were “surprised and excited” by the findings. So you may think okay, but what’s the big deal if the moon’s volcanoes lasted a longer?

Well, volcanoes don’t just happen. You need heat in order for volcanoes to happen, and 120 million years ago, the moon shouldn’t have had enough heat — or so we thought.

The heat for the Moon’s original volcanic activity primarily came from its formation. The Moon formed about 4.5 billion years ago, likely from debris ejected when a Mars-sized body collided with Earth. The intense heat generated during this violent impact, combined with the subsequent accumulation of molten material, created a molten, magma-filled Moon.

Over time, as the Moon began to cool, radioactive decay of elements like uranium, thorium, and potassium within its interior also contributed to sustaining volcanic activity for billions of years. This combination of residual heat from its formation and radioactive decay powered the Moon’s early volcanic eruptions.

The volcanic beads identified in the Chang’e-5 samples were found to contain high levels of potassium, phosphorus, and rare-earth elements, collectively known as KREEP elements. These elements are known to produce heat through radioactive decay, so the heat for this volcanism did come from radioactive materials.

Researchers suspect that even as the moon cooled down, concentrations of KREEP elements could have sustained smaller-scale volcanic eruptions much later into the Moon’s geological history. The heat generated by these radioactive elements might have been sufficient to produce small pockets of molten rock, leading to isolated volcanic eruptions, like those evidenced by the glass beads in the Chang’e-5 samples.

But this is far from confirmed.

New missions, new findings

The findings are so surprising that they may force us to rethink not just our moon, but moons in general. If they can maintain sufficient heat to sustain volcanism for so long, it could change our understanding of the evolution of moons.

Understanding the source of these volcanic eruptions could drive future missions to investigate the Moon’s interior and surface in greater detail. Thankfully, we’ve got a few of those lined up.

The Chang’e-5 mission marked China’s first successful return of lunar samples, but it is just one step in a series of planned missions. The Chang’e-6 mission, which retrieved samples from the far side of the Moon in June 2023, could provide additional data on volcanic activity in other regions of the lunar surface. With continued exploration and sample return missions, scientists hope to build a more comprehensive picture of the Moon’s volcanic history. India’s Chandrayaan-3 mission has also contributed to this growing body of knowledge. In 2023, its Pragyan rover discovered anorthosite rocks that scientists believe formed in an ancient ocean of magma, further supporting the idea that the Moon had a molten interior during much of its early history.

At the end of the day, it’s telling that even the moon (which is so in our solar “neighborhood” and which we’ve visited more than once) can surprise us so much. Who knows what other secrets hide in other moons?

The study was published in Science.