adjacent OMby the radioactive grains. The heat from the radioactive grains, however, found to have a negligible effect on the overall thermal maturity of these shales.

Kim, durans Kim, durans J., Chhetri, G., Kim, I., Kim, M.K., Seo, T., 2020. sp. nov., a radiation-resistant bacterium isolated from gamma ray-irradiated soil. Antonie van Leeuwenhoek 113, 211-220.

https://doi.org/10.1007/s10482-019-01331-2 A gamma radiation-resistant, Gram-stain negative, oxidase and catalase positive, aerobic, flagellated, rod- T shaped, methylotrophic and pink-pigmented bacterial strain designated 17SD2-17 was isolated from gamma- T ray-irradiated soil collected in Korea. The 16S rRNA gene sequence analysis showed that strain 17SD2-17 is T phylogenetically related to Methylobacterium organophilum DSM 760 (97.6%), Methylobacterium oxalidis T T 35a (97.4%) and Methylobacterium soli YIM 48816 (97.0%). The G+C content calculated based on the draft T genome sequence is 68.7 mol%. The DNA - DNA hybridisation between 17SD2-17 and its close relatives was found to be less than 40%. The predominant fatty acid was identified as summed feature 8 (C ω7c and/or 18:1 C ω6c) and the major respiratory quinone as Q -10. The major polar lipids were found to be 18:1 diphosphatidylglycerol, phosphatidylglycerol, and phosphatidylethanolamine. On the basis of the data from T phenotypic tests and genotypic differences between strain 17SD2-17 and its close phylogenetic relatives, strain T 17SD2-17 is concluded to represent a new species belonging to the genus Methylobacterium, for which the T T name Methylobacterium durans sp. nov. (= KCTC 52908 = NBRC 112876 ) is proposed.

King, S.D., 2020. Do impacts impact global tectonics? Geology 48, 205-206.

https://doi.org/10.1130/focus022020.1 Geodynamic calculations have become an important hypothesis-testing tool when combined with the Precambrian geological record (c.f., van Hunen and Moyen, 2012: O'Neill et al., 2018; Stern and Gerya, 2018). These models are based on basic laws of physics, including the conservation of mass and energy, as well as Newton's second law, sometimes misleadingly described as the conservation of momentum. To reduce the number of variables and create a set of equations that can be solved, a set of constitutive equations are required. For mantle convection, stress and strain rate are related through the viscosity. The viscosity of silicate minerals depends on temperature, pressure, composition, stress, grain size, water content, and history (c.f., King, 2016). Our understanding of viscosity is limited, in part due to the challenge of measuring the viscosity of silicate minerals at high pressures and temperatures, and the reality that the strain-rates achievable in such laboratory measurements must be extrapolated by orders of magnitude to mantle conditions. Geodynamic calculations are built upon solid physical principles; the calculations are limited in so far as our understanding of mantle viscosity is limited, and the appropriateness of the initial and boundary condition choices. Plate tectonics is the framework through which we understand the large-scale Phanerozoic history of Earth. The question of when and how plate tectonics began remains the subject of debate, in no small part because through subduction, plate tectonics destroys much of the evidence of its earlier activity. Estimates of the onset of plate tectonics vary from the Hadean (Hopkins et al., 2008), to the Archean (Brown, 2006), to the Neoproterozoic (Stern 2005, 2008). There is no rock record from the Hadean, and only a limited rock record from the Archean. Thus, it is unlikely that we will determine whether any deformation recorded during this time period was part of a globally connected plate boundary system or a regional, transient event. Spherule beds are preserved within Archean age rocks in the Barberton greenstone belt, South Africa (Lowe and Byerly, 1986; Lowe et al., 1989) and the Pilbara craton, Australia (Glikson et al., 2016). Archean spherule beds formed from the distal ejecta of large bolide impacts. These beds contain important clues regarding their formation - the thickness of the beds can be used to estimate the size of the impactor (Johnson and Melosh, 2012). Lowe et al. (2014) described four additional spherule beds and placed their formation at the same time as the first major episode of orogeny and crustal deformation in the Barberton greenstone belt (3.26 - 3.23 Ga). Lowe et al. further suggested that these impacts may have been the trigger that initiated the modern plate tecto nic regime. A new contribution by O'Neill et al. (2020, page 174 in this issue) uses the characteristics of these recently described spherule beds to constrain the size and velocity of the impactors that formed them,