\n<\/p>\n
What\u2019s the story of our Moon\u2019s early history? Despite all we know about our closest natural satellite, scientists are still figuring out bits of its history. New measurements of rocks gathered during the Apollo missions now show it solidified some 4.43 billion years ago. It turns out that\u2019s about the time Earth became a habitable world.<\/p>\n
<\/p>\n University of Chicago scientist Nicolas Dauphas and a team of researchers made the measurements. They looked at different proportions of elements inside Moon rocks. They provide a window into the Moon\u2019s early epochs. It started out as a fully molten blob after a collision between two early solar system bodies. <\/p>\n As it cooled and crystallized, the molten proto-moon separated into layers. Eventually, about 99% of the lunar magma ocean had solidified. The rest was a unique residual liquid called KREEP. That acronym stands for the elements potassium (K), rare earth elements (REE), and phosphorus (P).<\/p>\n Dauphas and his team analyzed this KREEP and found that it formed about 140 million years after the birth of the Solar System. It\u2019s in the Apollo rocks and scientists hope to find it in samples from the South Pole-Aitken basin. This is the region where Artemis astronauts will eventually explore. If analysis confirms it there, then it indicates a uniform distribution of this KREEP layer across the lunar surface.<\/p>\n The clues to the Moon\u2019s ultimate \u201ccooling off period\u201d lie in a faintly radioactive rare earth element called \u201clutetium\u201d. Over time, it decays to become hafnium. In the early Solar System, all rocks had about the same amounts of lutetium. Its decay process helps determine the age of the rocks where it exists.<\/p>\n However, the Moon\u2019s solidification and subsequent formation of KREEP reservoirs didn\u2019t result in a lot of lutetium compared to other rocks created at the same time. So, the scientists wanted to measure the proportions of lutetium and hafnium in Moon rocks and compare them to other bodies created around the same time\u2014such as meteorites. That would allow them to calculate a more precise time for when the KREEP formed on the Moon.<\/p>\n They tested tiny samples of Moon rocks and looked at the ratio of hafnium in embedded lunar zircons. Through that analysis, they found that the rock ages are consistent with formation in a KREEP-rich reservoir. Those ages are consistent with the formation of KREEP reservoirs about 140 million years after the birth of the solar system, or about 4.43 billion years ago. \u201cIt took us years to develop these techniques, but we got a very precise answer for a question that has been controversial for a long time,\u201d said Dauphas.<\/p>\n Interestingly, the team\u2019s results showed that lunar magma ocean crystallization occurred while leftover planetary embryos and planetesimals bombarded the Moon. Those objects were the birth \u201cseeds\u201d of the planets and Moon, which began after the Sun coalesced starting some 4.6 billion years ago. What remained from the formation of the planets continued to batter the already-formed planets.<\/p>\n The formation of the Moon itself began some 60 million years after the solar system itself was born. The most likely event was the collision of a Mars-sized world called Theia with the infant Earth. That sent molten debris into space and it began to coalesce to make the Moon. \u201cWe must imagine a big ball of magma floating in space around Earth,\u201d said Dauphas. Shortly thereafter, that ball began to cool. That process eventually resulted in the formation of the lunar KREEP layers.<\/p>\nUnderstanding KREEP\u2019s History on the Moon<\/h3>\n
Placing KREEP in Perspective<\/h3>\n