On the basis of these crystals the researchers have gained important new insights into the history of the moon's development. Their results are presented in the latest issue of the prestigious Nature Geoscience magazine.
Dr. Thorsten Geisler-Wierwille from the Institute of Mineralogy at the University of Münster has been examining tiny zircon crystals with his colleagues from Australia and the USA. The crystals come from moonrock already collected 36 years ago on the Apollo 17 mission. With the the help of modern microanalytical processes and uranium-lead dating the scientists have ascertained the age of the crystals. The oldest zircon they found is about 4.4 billion years old.
This very precise dating of the crystals' age enables the scientists to reconstruct for the first time, and more accurately, the crystallization and cooling history of the magma ocean on the moon. This magma ocean was formed after a collision around 4.5 billion years ago between the young Earth and a proto-planet the size of Mars.
"Any reconstruction of the cooling history was only possible to a limited extent before this," says Geisler-Wierwille, "because isotope systems that could have been used to ascertain age were badly damaged by intense meteorite impacts on the moon around 3.9 billion years ago. However, the uranium-lead dating system is very stable in the face of extreme pressures and temperatures and is therefore highly suitable for establishing how long ago things were formed."
The crystallization of zircon in the lunar magma indicates that at this point there was only a small quantity of magma still in existence. The scientists conclude that almost the entire magma ocean was solidified 100 million years after the moon was formed.
Dr. Geisler-Wierwille made the headlines once before with the discovery of especially old crystals. He and Martina Menneken from the WWU's Institute of Mineralogy belong to a team of researchers who in 2007 found the oldest diamonds in the world.
Dr. Christina Heimken | idw
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