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One of the oldest rocks on Earth appeared on the Moon, from all places

According to the Giant Impact Hypothesis, the Earth-Moon system was created about 4.5 billion years ago when an object the size of Mars collided with Earth. This impact led to the release of huge amounts of material that eventually came together to form the Earth and the Moon. Over time, the Moon gradually migrated from Earth and assumed its present orbit.

Since then, there have been regular exchanges between Earth and Moon due to impacts on their surfaces. According to a recent study, an impact that occurred during Hadean Eon (about 4 billion years ago) may have been responsible for sending the earliest rock sample from Earth to the Moon, where it was recovered by rock. Apollo 14 astronauts

The study, which appeared recently in the journal Letters of the Earth and Planetary Sciencewas led by Jeremy Bellucci of the Swedish Museum of Natural History, and included members of the Lunar and Planetary Institute (LPI), various universities and the Center for Science and Lunar Exploration (CLSE), which is part of the NASA. Virtual Institute.

This finding was made possible by a new technique developed by the study team to locate impactor fragments in lunar regolith. The development of this technique led Dr. David A. Kring – the principal investigator of the CLSE and a scientist from the University Space Research Association (USRA) of the LPI – to challenge them to locate a piece of the Earth on the Moon.

The resulting investigation led them to find a 2 g (0.07 oz) rock fragment composed of quartz, feldspar and zircon. Rocks of this type are commonly found on Earth, but are highly unusual on the Moon. In addition, a chemical analysis revealed that the rock crystallized in an oxidized system and at temperatures consistent with the Earth during the Hadean; instead of the Moon, which was experiencing higher temperatures at the time.

As Dr Kring pointed out in a recent LPI press release:

"It's an extraordinary find that helps paint a better picture of the early Earth and the bombardment that changed our planet during the dawn of life."

Based on their analysis, the team concluded that the rock was formed in the Hadean Eon and was launched from Earth when a large asteroid or comet impacted the surface. This impact would have released material in space where it collided with the surface of the Moon, which was three times closer to Earth at the time. Eventually, this rocky material mixed with the lunar regolith to form a single sample.

The Moon was much closer The Earth is what it is today when the rock fragment was produced and ejected from Earth to the Moon in a major impact event. Credit: LPI / David A. Kring.

The team can also learn a lot about the history of sample rock from their analysis. On the one hand, they concluded that the rock crystallized to a depth of about 20 km below the surface of the Earth, between 4.0. and 4.1 billion years ago, and was then excavated by one or more large impact events that sent it into the cis-lunar space.

This is consistent with previous team research that showed how impacts during this period – that is, Late Heavy Bombardment (which occurred about 4.1 to 3.8 billion years ago) – produced craters thousands of kilometers in diameter , more than enough to eject material from a depth of 20 km (12.4 mi) in space.

They also determined that several other impact events affected him when they hit the lunar surface. One of them caused the sample to merge about 3.9 billion years ago, and could have buried it below the surface. After this period, the Moon was subjected to smaller and less frequent impacts, giving it the bumpy surface it has today.

The final impact event affecting this sample occurred about 26 million years ago during the Paleogene period on Earth. This impact produced the Cone Crater of 340 m (1082 ft) in diameter and excavated the sample rock back to the lunar surface. This crater was the landing place of the Apollo 14 mission in 1971, where mission astronauts obtained rock samples to bring back to Earth for study (which included Earth rock).

The artists impression of the period of the late heavy bombardment, which occurred ca. 4.1 to 3.6 billion years ago. Credit: NASA

The research team recognizes that it is possible that the sample has crystallized on the Moon. However, this would require conditions that have yet to be observed in all the lunar samples obtained so far. For example, the sample would have to crystallize very deeply into the lunar mantle. In addition, it is believed that the composition of the Moon at these depths is quite different from that observed in the sample rock.

As a result, the simplest explanation is that this is a land rock that ended on the Moon, a discovery that is likely to generate some controversy. This is unavoidable, since this is the first Hadean sample of this type to be found, and the location of its discovery can also increase the factor of unbelief.

However, Kring anticipates that more samples will be found, since the hadean rocks would probably have splashed the lunar surface during the Late Heavy Bombardment. Perhaps when manned missions begin to travel to the Moon in the next decade, they will find more of the oldest rock samples on Earth.

The research was made possible by support provided by the NASA Solar System Exploration Virtual Research Institute (SSERVI) as part of a joint venture between LPI and the NASA Johnson Space Center.

Additional Reading: LPI, Letters of the Earth and Planetary Science

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