The Moon was volcanically active as late as 120 million years ago

Unlike today, the Moon was once volcanically active. But exactly how long this period of volcanism persisted remains unclear.

New analysis of lunar samples returned by the Chang’e-5 mission by the China National Space Administration suggest volcanic eruptions were occurring on the Moon as little as about 120 million years ago.

The new findings, published in a paper in Science, represents the youngest instance of lunar volcanism confirmed by radiometric dating so far.

Dating of lunar volcanic rocks, “basalts”, from the Apollo and Luna missions indicates that the Moon was volcanically active as early as 4.4 billion years ago. Previous analysis of samples returned to Earth by the Chang’e-5 Lunar mission provided evidence of volcanic activity 2 billion years ago.

For this new study, researchers analysed approximately 3,000 microscopic glass beads handpicked from Chang’e-5 lunar soil samples.

These beads can be created by 2 distinct processes: the intense heat and pressure of meteorite impacts, or from lava fountains generated by the eruption of gas-rich magma.

Based on their textures, major- and trace-element compositions, and sulphur isotope analyses, the researchers identified 3 glass beads of volcanic origin.

Radiometric uranium-lead dating – a technique that measures the ratio of uranium isotopes to stable lead isotopes – revealed the beads formed 123 million years ago (plus or minus 15 million years).

“That date is consistent with indications of young volcanic activity on the Moon from remote sensing observations, which did not provide absolute dates,” the authors write in the paper.

They say it is unclear how the Moon could have remained volcanically active at such a late stage.

“As the interior cooled and the lithosphere thickened, volcanic activity would have become less likely,” they write.

A low and continually declining rate of volcanism may explain the roughly 1.9-billion-year gap between eruptions recorded at the Chang’e-5 landing site.

“The effort that Wang et al. put into finding the volcanic “needle” in the impact-generated “haystack” has paid off,” write Yuro Amelin of the Korea Basic Science Institute, and Qing-Zhu Yin of the University of California at Davis in the US, in a related Perspective.

“It will add to the ongoing debates about thermal evolution of planetary bodies and the question of how planets cool, which is not yet known.”