The age of the Moon has been called into question by Apollo samples

New post in Geochemical Perspectives Letters It shows that the legacy of the Apollo missions is still very much alive, even more than 50 years after the unforgettable arrival of representatives of the nucleosphere to the planet’s surface. moonmoon. Therefore, hundreds of lunar rocks and soil samples have been brought back by cosmochemists and planetary scientists in the field AstronautsAstronauts toApollo 11Apollo 11 on Apollo 17. They have always been sources of inspiration for these researchers, who take advantage of modern tools to analyze the planet’s isotopic composition. MetalsMetals These rocks are formed.

Indeed, in the early 1970s, lunar samples were being studied by the famous “four horsemen” of the Apollo program, geochemists by training – Gerald Wasserburg Along with Bob Walker, Jim Arnold and Paul Werner Gast – they really began to appear gossip. Gerald Wasserberg and his colleagues had done work that would lead to the development of today’s generally accepted model for the origin of the Moon, which was the collision between a Mars-sized planet called Theia and a young Earth.

This collision must have occurred no more than a few hundred million years after the planet’s formation Solar systemSolar system Including study MeteoritesMeteorites It indicates that it must be 4.56 billion years old, give or take a few million years.

Study of lunar rocks tells us that shortly after its birth, the Moon must have been covered by a massive global ocean of… The son-in-lawThe son-in-law Which, as they cool, crystallize according to various processes that we know how to reproduce on Earth by studying the magmatic processes that lead to terrestrial igneous rocks.

Have you ever wondered how the dark and bright areas of the moon are formed? In this short video you’ll learn how they emerged from an ancient moon, surrounded by an ocean of magma. The video was produced by Professor Tim Swindle, of the Lunar and Planetary Laboratory at the University of Arizona, part of the LPI-JSC Lunar Science and Exploration Center. For a fairly accurate French translation, click on the white rectangle at the bottom right. The English translation should appear next. Then click on the nut to the right of the rectangle, then on “Translations” and finally on “Translate automatically.” Select “French”. © Lunar and Planetary Laboratory, University of Arizona

Zircon memory

However, among the samples returned by Apollo 17 in 1972, a group of researchers found crystals that were produced during the cooling of the magma ocean. These are zircons and we know them well on Earth. These are the minerals that make up a group of SilicatesSilicatesmore accurate NisosilicatesNisosilicatesIts chemical formula is ZrSiO₄. It appears as one of the early products of the initial crystallization of Igneous rocksIgneous rocks It is particularly stable, which means that it not only passes for long periods of time without changing, but above all, it maintains an amount of…IsotopesIsotopes Which it contained during its formation, along with radioactive decay products of course. Thus we can date zircon faithfully and accurately. On our blue planet, this also provides information about ancient plate tectonics and other processes that may date back to the Paleocene, or even the Hadean Era.

In this case, the zircon that was found and studied analytically, using the so-called tomographic atomic probe, pushes the age of the Moon back by 40 million years, to at least 4.46 billion years. They were necessarily formed during the crystallization of the lunar magma ocean.

Radioactive dating of uranium and lead

” These crystals are the oldest solidsolid It is known that it was formed after a giant collision. Because we know the age of these crystals, they serve as an anchor to the lunar timeline », explains in a press release Philip Heck, curator of the museum Field Museum Robert A. Pritzker For meteorites, she is a professor at the University of Chicago and lead author of the study published with Jenica Greer, when she was a doctoral student at the University of Chicago. Field Museum And the University of Chicago.

The dating conducted by the researchers is typical of that used with isotopesUraniumUranium And leads, the former disintegrates into the latter RadioactivityRadioactivity. As it crystallizes, the zircon crystals will be held firmly and loosely Radioactive contaminationRadioactive contamination The outer layer over several billion years is a mixture of different isotopes. That uranium will behave next sandsand Of the hourglass in front of the lead cores. The more time passes, the more lead cores we have. This is a classic example, among others, of radiometric dating.

This is the ratio of lead isotopes found by the researchers, which indicates that the age of the sample studied was about 4.46 billion years, and therefore the moon must be at least this age.