Three small glass beads taken from the surface month It turns out that Earth’s largest natural satellite’s turbulent past wasn’t all that long ago after all.
These once-molten minerals provide evidence of lunar volcanic activity that occurred just 120 million years ago, according to a thorough and careful new analysis of material collected by the China National Space Administration’s Chang’e-5 mission.
This is much later than expected for such activity on the Moon, which was very volcanically active between about 4.4 billion and 2 billion years ago, after which it is thought the Moon cooled too much for any significant volcanic activity to occur.
This discovery makes it clear that the Moon still has many secrets to reveal — and we may need to go to the Moon to find out.
“Radioisotope dating of the three volcanic glass beads from Chang’e-5 has revealed the truth that volcanic activity occurred on the moon’s surface 120 million years ago,” He Yuyang, a geophysicist at the Institute of Geology and Geophysics, Chinese Academy of Sciences, told Science Alert.
“There is a gap of about 1.9 billion years between eruptions recorded at the landing site. The presence of volcanism on such a young Moon implies that a small body like the Moon can retain enough heat to sustain internal vitality until very late stages.”
When Chang’e-5’s lunar dust samples are delivered to Earth’s surface in late 2020, they will be the first lunar material made available to humanity since the last Soviet lunar probe returned in 1976. Scientists around the world are sifting through this new lunar debris using a variety of analytical techniques to dig into it and gain new insights into the moon’s geology and history.
One particularly interesting component of the sample is the minuscule glass spheres, which form when minerals melt and then harden back into glass under harsh conditions. The glass particles may be contaminated with other lunar materials, which could be used to study the conditions under which the glass formed, including the composition of surrounding lunar rocks at the time.
A team led by geophysicists Wang Biwen and Zhang Qian WL of the Chinese Academy of Sciences sifted through about 3 grams (0.1 ounce) of lunar dust from Chang’e 5. From just a teaspoon of the material, they were able to isolate about 3,000 glass spheres.
Most of these are the result of meteorite impacts, and the volcanic particles are the real needles in the haystack: Because the Moon is prone to many impacts but very little volcanism, researchers have had a hard time identifying which, if any, spherical particles are the product of the latter.
“First, we used backscattered electron imaging to identify approximately 800 glass beads without obvious compositional changes or undigested inclusions that are characteristic of an impact,” he explained.
“We then analyzed selected beads using an electron probe microanalyzer. Only 13 glass beads had similar major element compositions to the Apollo volcanic glass beads. Based on trace element composition, 6 of the 13 glasses have correlations of magnesium oxide and nickel abundances that tend to be the same as the volcanic glasses identified in the Apollo samples. All of the above evidence is inconclusive.”
Finally, they performed sulfur isotope analysis using secondary ion mass spectrometry. Three of the last six spherules showed sulfur ratios that didn’t match impact glass. They had a hit: this was volcanic glass.
But then Radiometric dating The globules were dated to 123 million years ago (with a margin of error of 15 million years), much younger than the moon’s last volcanic activity.
It’s unclear how this happened, as the Moon has long been too cold for volcanic activity, but clues may lie in the chemicals trapped in the three spheres: They contain high concentrations of so-called KREEP elements, including potassium, rare earth elements, and phosphorus.
These high KREEP levels can cause radioactive heating, the heat generated by radioactive decay. This heating can be significant. About half of the Earth’s internal heat is It is caused by radioactive decay.On the Moon, radioactive heating could theoretically lead to localized volcanic activity.
Further research may reveal whether there is enough KREEP material in the lunar mantle to form these pockets.
“It is unclear why the Moon was able to sustain volcanic activity so late in its lifespan. As the interior cools and the lithosphere thickens, volcanism should become less likely,” he said.
“Where did these volcanic glass beads come from? Was there other volcanic activity between 2 billion and 120 million years ago? What caused it? Further research is needed.”
This study Science.
