Mare volcanics on the Moon are the key record of thermo-chemical evolution throughout most of lunar history1–3. Young mare basalts—mainly distributed in a region rich in potassium, rare-earth elements and phosphorus (KREEP) in Oceanus Procellarum, called the Procellarum KREEP Terrane (PKT)4—were thought to be formed from KREEP-rich sources at depth5–7. However, this hypothesis has not been tested with young basalts from the PKT. Here we present a petrological and geochemical study of the basalt clasts from the PKT returned by the Chang’e-5 mission8. These two-billion-year-old basalts are the youngest lunar samples reported so far9. Bulk rock compositions have moderate titanium and high iron contents  with KREEP-like rare-earth-element and high thorium concentrations. However, strontium–neodymium isotopes indicate that these basalts were derived from a non-KREEP mantle source. To produce the high abundances of rare-earth elements and thorium, low-degree partial melting and extensive fractional crystallization are required. Our results indicate that the KREEP association may not be a prerequisite for young mare volcanism. Absolving the need to invoke heat-producing elements in their source implies a more sustained cooling history of the lunar interior to generate the Moon’s youngest melts.

The effects of oxygen radicals on sterilization were studied using a 2.45 GHz surface-wave oxygen plasma. A population of 1.5ϫ 10 6 Bacillus stearothermophilus spores was irradiated for 3 min or more with oxygen plasma, generated at pressures between 6 and 14 Pa. The decimal reduction value ͑D value͒, a measure of the effectiveness of sterilization, was determined to be about 15-25 s. Using only oxygen radicals, excluding all charged particles, the 1.5ϫ 10 6 spores were sterilized with a D value of 30-45 s after 5 min or more of irradiation. On scanning electron microscopy, the length and width of the spores changed significantly due to chemical etching by oxygen radicals.

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The CF 2 density and etch rate of SiO 2 , Si 3 N 4 and Si are investigated as a function of gas pressure and O 2 flow rate in fluorocarbon plasma. As the pressure increases, the self-bias voltage decreases whereas the SiO 2 etch rate increases. Previous study has shown that SiO 2 etch rate is proportional to the self-bias voltage. This result indicates that other etching parameters contribute to the SiO 2 etching. Generally, the CF 2 radical is considered as a precursor for fluorocarbon layer formation. At a given power, defluorination of fluorocarbon under high-energy ion bombardment is a main source of fluorine for SiO 2 etching. When more CF 2 radical in plasma, SiO 2 etch rate is increased because more fluorine can be provided. In this case, CF 2 is considered as a reactant for SiO 2 etching. The etch rate of Si 3 N 4 and Si is mainly determined by the polymer thickness formed on its surface which is dominated by the CF 2 density in plasma. Etching results obtained by varying O 2 flow rate also support the proposition.

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