Is the moon older than expected?

New analyzes of Apollo samples suggest that they were formed 4.51 billion years ago

The moon may have originated earlier than previously thought - 4.51 billion years ago. © NASA
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Early Origin: Researchers have re-dated the formation of the moon. Thus, the catastrophic collision that emerged from the Earth's Grave occurred 4.51 billion years ago - only about 50 million years after the solar system was born. The evidence for this dating provided, inter alia, isotope ratios in lunar rock samples that were returned 50 years ago by the Apollo astronauts to Earth.

The earth's moon is the result of a cosmic catastrophe - the collision of the young earth with a protoplanets of the size of Mars. This left a glowing, damaged earth and a circle of debris around it, from which the moon formed. According to popular belief, the earth's moon was initially covered by a magma ocean, which then gradually cooled.

But when did this big catastrophe happen? So far, researchers are at odds: Some date the lunar origin to a good 4.5 billion years, younger studies, however, report evidence for an age of just under 4.4 billion years. In both cases, the dating is based on the chemical and isotopic composition of moon rock samples returned by the Apollo astronauts some 50 years ago.

Moonstone: This sample is an ilmenite basalt collected during the Apollo 12 mission. Maxwell Thiemens 2019

R tsel to tungsten excess

Now Maxwell Thiemens from the University of K ln and his team have re-examined some of the Apollo samples. Their dating is based on the ratio of the radioactive isotope hafnium-182 to tungsten-182. It has long been known that some lunar basalts have a higher proportion of tungsten compared to the earth.

In previous studies, some researchers had explained this excess by saying that the young earth was more frequently hit by meteorites than the moon because of its larger surface area. These were rather tungsten-poor and thus changed the element ratio stronger than the moon. According to another theory, the increased tungsten content of the lunar rock could also be one
Indica- tion that these rocks were formed at a time when there was still a lot of hafnium-182 that could decay to tungsten. display

Test with isotope analyzes and model simulations

Which of these theories might be correct has now been checked by Thiemens and his team. They analyzed different rock samples from the Moon to the ratio of hafnium to tungsten and from uranium to tungsten. The result: The combined isotope shares confirm that especially the lunar basalts have a significantly higher proportion of tungsten than the terrestrial mantle rocks.

Using a model, the researchers then determined whether these isotope ratios can be explained by meteorite impacts or by a young age of the moon. For this they simulated a scenario with a late formation of the moon and a strong meteor bombardment and two different variants of an early moon formation.

Why the moon could be older than thought. Universit t to K ln

50 million years after the formation of the solar system

After evaluating all the results, the researchers come to the conclusion: "The lunar differentiation must have occurred 40 to 60 million years after the formation of the solar system, " said Thiemens and his team. It is believed that the solar system was born 4.56 billion years ago. According to this, the moon must be around 4.51 billion years old. It could therefore be significantly older than the previously assumed 4.36 or 4.4 billion years.

"That may sound very similar for an outsider, but it is striking for us geoscientists, " explains senior author Carsten M nker from the University of K ln, "Because that also changes models, for example, as to when the earth originated." (Nature Geoscience, 2019; doi: 10.1038 / s41561-019-0398-3)

Source: University of Cologne

- Nadja Podbregar