Volcanic moon rocks brought back to earth from the NASA Apollo missions have isotopic signatures that offer insights into our Moon's early history, a new analysis reveals.
The events in question include the formation of the Moon's dense and metallic core and the crystallization of the lunar magma ocean - a sea of molten rock and metal believed to cover the Moon's surface for about a hundred million years after its formation.
Researchers reported their findings in the latest journal Science Advances, titled "Large sulfur isotope fractionation in lunar volcanic glasses reveals the magmatic differentiation and degassing of the Moon." They detail using a method called secondary ion mass spectrometry (SIMS) to conduct the new analysis of the volcanic glass specimens taken back to Earth by the Apollo 15 and 17 missions. These samples are believed to be among the oldest materials from the Moon.
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Isotopes on Volcanic Rocks: Hints at the Moon's Early History
The study particularly focuses on the sulfur isotope concentrations, which could offer insights into the chemical changes that occur on Moon lava from their generation, transport, and eruption.
"For many years, it appeared as though the lunar basaltic rock samples analyzed had a very limited variation in sulfur isotope ratios," explains Alberto Saal, co-author of the study and a geology professor at Brown University, in a press release from the University. He adds that this finding suggests the Moon interior having a "basically homogenous sulfur isotopic composition."
He adds that with the use of modern analytical techniques, they demonstrated that the isotope ratios of the volcanic glass samples have a wide range, with these differences corresponding to events in the Moon's history.
Researchers compared the ratio between the "heavy" sulfur-34 isotope with the "lighter" sulfur--32. Initial analyses of the moon rock samples showed tendencies towards the heavier sulfur isotope. Furthermore, the most homogenous sulfur isotope ratio was also contrasting with the large variations in other isotopes found in the moon rock samples.
Examining Pure Lava Within The Moon Rocks
Researchers examined 67 individual volcanic glass samples and melt inclusions in the new study, which are small blobs of molten lava trapped inside the glass. These melt inclusions preserve lava samples before the release of sulfur, and other chemicals are released in gaseous forms during an eruption in a process called degassing. Therefore, these samples are valuable since they are unadulterated samples of the original lava source.
Using the SIMS located at the Carnegie Institution for Science, researchers measured the sulfur isotopes, which were then used to calibrate an existing model of lava degassing to be used across all samples.
"Once we know the degassing, then we can estimate back the original sulfur isotope composition of the sources that produced these lavas," Saal added.
Based on their calculations, the lava recovered from the samples was found to have come from different reservoirs in the Moon's interior with different sulfur isotope ratios. This, in turn, could offer insights as to which early Moon history event caused the creation of these samples.
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