October 26, 2021

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The rocks brought by China show that the moon maintained its volcanic activity until more recent dates. Science

The rocks brought by China show that the moon maintained its volcanic activity until more recent dates. Science

Since 1976, when the Soviet Lunik 24 mission returned from the moon with a few grams of soil, no one has gone to the satellite for more. were the Chinese, with your probe Chang’e-5, those who returned from there in December of last year with about two kilograms of lunar material. Now the magazine Science The results of a study of two of those rocks are published. It is volcanic, similar in composition to Earth, and has been shown to be much newer than previously thought. This changes the date of the neighboring star and they have connections to Earth.

The Apollo missions of the United States brought nearly 400 kilograms between Earth and lunar rocks. Analyze the first, such as baptismal stone origin, allowed to date the origin of the moon about 4500 million years ago. Despite its variable composition, its constituent elements are also present on Earth. Most of them are of volcanic origin, from magma that emerged through cracks, crystallized and cooled long ago.

All this led to the rewriting of the history of the satellite, which, like many other celestial bodies, was thought to have been formed by particle accretion. But, as I said in This article is from 2019 Rick Carlson, a geochemist and director of the Geomagnetic Division at the Carnegie Institution for Science, “with the first samples of Apollo 11, we realized that the moon formed hot, perhaps completely melted. Upon cooling from this initial state, it generated a thick crust by means of crystals floating in the cooled magma.” The Americans estimated that the basaltic rocks that were brought to Earth originated about 3 billion years ago, at which time the hot lunar phase transitioned to the present cold age, where A reduced mineral core and a thermally dead mantle complete the internal structure, but now Chinese and American researchers have found smaller volcanic rocks.

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Scientists from the Institute of Geology of the Chinese Academy of Geosciences published in Science Petrographic and geochemical analysis of two small rocks carried out by the space probe they change It was brought from the moon. The first thing they discovered was that it crystallized in its solid state 1963 million years ago, 50 million above or below. This means that the Moon’s surface was still, at least partially, molten, or had a thermally active mantle about a billion years later than previously thought.

One of the moon rocks analyzed in the study. Both were collected from the northern Oceanus Procellarum.

Director of the McDonnell Center for Space Science at Washington University in St. Louis (US) Brad Jolev A decade of collaboration with Chang’e . Expedition Scholars. Jolliff, co-author of this study, recalls that “All the volcanic rocks I collected Apollo They were more than 3000 million years old.” He adds at the same time that “all the impact craters dated from the analysis of these samples are less than 1000 million years old.” Therefore, he concludes, “Samples from Chang’e-5 They fill a critical void.”

In fact, to write the history of the moon, scientists relied on two components: on the one hand, the age of the rocks, which is estimated by differences in some of the radioactive elements present in them, such as isotopes of lead. Another mainstay of the lunar chronology is the craters. In a simple version of this dating technique, the greater the effects on a particular area of ​​a satellite, the older it must be. In fact, those responsible for the mission Chang’e-5 They chose the area north of Oceanus Procellarum for landing on the moon because it is one of the areas with the least cratering density, that is, it is newer. Now, with the new samples, they will be able to improve knowledge of the lunar past.

The study also details the moon’s rock formation. The most abundant mineral is pyroxene, followed by plagioclase (something similar to terrestrial basalt, but with greater abundances of ilmenite, iron oxide and titanium) than these, which is a natural thing in lunar basalt. Actually a rock not much different from the lava that forms in the La Palma eruption.

But these two pebbles, less than four millimeters in size, could also shed light on still-dark periods in Earth’s evolution. On the planet, the Earth’s crust is floating on a more or less liquid cover. This one cracks in tectonic plates and is found in it, like oceanic ridges or subduction zones, where one plate sinks under the other, where magma emerges. But there are other ways in which the mantle releases heat and pressure: so-called hot spots (Attractions, In English). These are areas of high volcanic activity but are far from the ridges and collisions between the plates. On them and because of them, a significant part of the oceanic islands was formed: Hawaii, Easter, Azores or Canary Islands.

Domingo Gimeno, professor of petrology at the University of Barcelona, ​​“Everyone thought they died from a thermal point of view a billion years ago from these rocks. So, what happened to the 1,000 million reactivation later? The authors do not provide a conclusive answer, but it is possible that hotspots similar to those on Earth have been preserved in highly localized regions of the mantle, giving rise to these igneous rocks.

“thanks for the tectonic plates You can go back about a billion years, but there will come a time when we don’t have proof of how things work here. on the moon [donde no hay placas tectónicas] You have something similar to Hotspot Which is two billion years old. These give you an idea of ​​what the flow of heat and matter toward the Earth’s crust might have been like when it was still not working with plate tectonics,” says Jimeno. For him, in his assessment of this research, “It’s not about what they found, but what others will see.” [en estas rocas]As a key to reading the ancient land of which we have hardly any evidence.”

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