The Americans brought from the moon the oldest known rock on Earth. Scientists suggest that the substance formed on Earth, and then was thrown out by the impact of an asteroid and ended up on the Moon.
The oldest terrestrial rock known to scientists has been discovered, and it is probably found on the moon. The rock is contained among the samples of lunar soil delivered during the third landing of American astronauts on the moon as part of the Apollo 14 expedition.
The study, published in the journal Earth and Planetary Science Letters, involved scientists from Australia, Sweden, Britain, the Netherlands and the United States, including researchers from NASA's scientific departments.
In their study, scientists found evidence that one of the samples collected by astronauts is in fact of terrestrial origin and was thrown from our planet in the early era of its formation - in a geological period called Katarchea, which is counted from the time of the formation of the Earth (approximately 4.6 billion years) up to 4 billion years.
This is a sample of lunar breccia, which was delivered to Earth under the number 14321. Of particular interest in the sample under study were quartz, zircon (ZrSiO4) and feldspar, which are widespread in terrestrial rocks and are extremely rare on the Moon.
The chemical analysis carried out showed that, with a high probability, crystallization of these minerals occurred precisely in terrestrial conditions in the presence of oxygen, at relatively low terrestrial temperatures and not at higher lunar temperatures, which are believed to have been in that era.
“This is an outstanding find that allows us to paint a picture of the early Earth and the bombardment that reshaped our planet at the dawn of life,” explained David King of the University Space Research Association (USA).
According to scientists, the material could be thrown out of the Earth when hitting its surface by a meteorite or comet. Having overcome the layers of the ancient primitive Earth's atmosphere and got into space, this material, in the end, ended up on the surface of the Moon, which at that time was about three times closer to the Earth than it is today. Later, this substance mixed with other lunar rocks and was among the samples delivered by astronauts to Earth.
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Scientists admit that it is not completely certain that the samples studied are of terrestrial origin, and in fact did not crystallize on the Moon. However, in the case of lunar origin on the Moon, such conditions must have existed in the distant past, evidence of which was never found in samples delivered from the Earth's satellite.
Such conditions could exist only at very great depths on the Moon, in the mantle, where scientists assume a completely different mineralogical composition of rocks.
“Thus, the simplest explanation is that the sample got there from the Earth,” the researchers conclude.
The analysis revealed something more about the sample. These rocks crystallized at a depth of about 20 kilometers under the Earth's surface 4-4.1 billion years ago and were thrown out and into the near-earth space after the impact of some cosmic body.
Past studies have shown that during that era, asteroid collisions were quite frequent, and they could form craters on the Earth's surface thousands of kilometers in diameter, which is enough to lift rocks from such a depth to the surface.
The study showed that, having hit the surface of the moon, the material experienced several more impacts, as a result of one of them, 3.9 billion years ago, it partially melted again and ended up under the surface.
All of this indicates that the collected material is a direct witness to the era of the late heavy bombardment, which in the first billion years shaped the appearance of the future solar system.
According to modern concepts, the Moon was formed about 4.5 billion years ago as a result of a collision of proto-earth with another planet about the size of Mars.
In the subsequent epoch, the Earth was bombarded by celestial bodies called planetesimals, which the young solar system was rich in, and which, due to the attraction of new material to themselves, became the embryos of future planets.
After this era, the Moon was hit by much smaller asteroids and much less frequently. The last impact of the studied sample experienced 26 million years ago, when the impact of a meteorite formed the Cone crater with a diameter of 340 meters, where it was picked up by the crew of the Apollo 14 lunar expedition almost 48 years ago (January 31 - February 6, 1971).