Fragments of Rock Uncover the Moment the Moon Became Solid

The early history of the Moon remains a topic of scientific investigation. Despite extensive knowledge about Earth’s natural satellite, some pieces of its history are still being unraveled.

Recent studies of rock samples collected during the Apollo missions have provided new insights, revealing that the Moon solidified approximately 4.43 billion years ago—around the same time Earth became capable of sustaining life.

Team of Researchers Pinpoints the Solidification Timeline

A team led by Nicolas Dauphas from the University of Chicago analyzed the composition of Moon rock fragments. By studying the different proportions of elements in the rocks, they gained valuable information about the Moon’s early stages. Initially, the Moon was a molten mass, formed by a collision between two early Solar System bodies

As the Moon cooled, the molten material began to crystallize, eventually forming separate layers. Nearly 99 percent of the lunar magma ocean solidified, leaving behind a unique residual liquid known as KREEP, which stands for potassium (K), rare earth elements (REE), and phosphorus (P).

Dauphas and his team examined the KREEP in the rocks, discovering that it formed roughly 140 million years after the Solar System’s birth. This finding is based on Apollo rock samples, with scientists eager to further explore the South Pole-Aitken basin, a region set to be visited by Artemis astronauts. If KREEP is present there, it would suggest a consistent distribution of this material across the Moon’s surface.

The team identified key clues about the Moon’s cooling process in the decay of a rare earth element called lutetium. Over time, lutetium decays into hafnium, and its presence in rocks helps determine their age. The Moon’s solidification and formation of KREEP resulted in much less lutetium compared to other contemporaneous rocks.

Breakthrough in Understanding the Moon’s Early Cooling

By analyzing tiny samples of Moon rocks, Dauphas’ team measured the hafnium-lutetium ratio within lunar zircons. This analysis confirmed that the rocks formed in a KREEP-rich reservoir, with ages indicating the formation of these reservoirs around 4.43 billion years ago—roughly 140 million years after the Solar System’s formation.

Interestingly, the team’s findings suggest that the crystallization of the lunar magma ocean occurred during the period when leftover planetary embryos and planetesimals bombarded the Moon. These objects, remnants from the Solar System’s formation, continued to impact the early planets, including Earth and the Moon.

The Moon’s formation likely began around 60 million years after the Solar System’s birth, following a collision between a Mars-sized planet called Theia and the early Earth. This collision launched molten debris into space, eventually coalescing to form the Moon. As the Moon cooled, it developed KREEP layers, marking an essential milestone in its history.

The decay of lutetium into hafnium in KREEP rocks marks a significant step in understanding the Moon’s earliest phases. Future rock samples from the South Pole-Aitken basin will help scientists fill in more gaps in the Moon’s history, particularly regarding the formation of mare basalts and the cooling of lunar rock.

Timing of Lunar Cooling and Its Earthly Significance

Determining the exact timing of lunar cooling not only reveals the Moon’s history but also sheds light on Earth’s evolution. The impact that formed the Moon was likely the last major collision Earth experienced, marking a turning point toward a more stable environment capable of supporting life.

“This discovery aligns with other evidence,” said Dauphas. “It sets the stage for even more revelations about the Moon, especially as the Chang’e and Artemis missions move forward. There are still many unanswered questions waiting for us.”

Read the original article on: Science Alert

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