The Moon’s youngest mare volcanism required a KREEP-rich mantle source enriched in heat-producing elements.

The dark plains visible across much of the Moon are ancient lava flows. Some of these mare basalts are much younger than most lunar volcanism, raising a basic question: what kept parts of the Moon hot enough to melt so late in its history?

One leading explanation focused on KREEP. Its radioactive elements release heat as they decay, and many young mare basalts occur in the Procellarum KREEP Terrane. It was therefore reasonable to suspect that this extra heat was directly tied to their source.

Chang’e-5 made that idea testable by returning rocks from one of the Moon’s youngest volcanic regions. The basalts are about 2 billion years old, but their isotope signatures point to a chemically depleted part of the lunar mantle with little KREEP contribution.

KREEP still matters to the Moon’s thermal and chemical history. What changed was the narrower claim that a KREEP-rich mantle source was required for very late lunar volcanism. The Chang’e-5 samples show that some young lunar lava came from somewhere else, so other processes must also have helped the Moon remain volcanically active.