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1. The role of impacts on Archaean tectonics

   https://doi.org/10.1130/G46533.1  

   O’Neill, C.; Marchi, S.; Bottke, W.; Fu, R. (November 2019, Geology)

   Abstract Field evidence from the Pilbara craton (Australia) and Kaapvaal craton (South Africa) indicate that modern tectonic processes may have been operating at ca. 3.2 Ga, a time also associated with a high density of preserved Archaean impact indicators. Recent work has suggested a causative association between large impacts and tectonic processes for the Hadean. However, impact flux estimates and spherule bed characteristics suggest impactor diameters of <100 km at ca. 3.5 Ga, and it is unclear whether such impacts could perturb the global tectonic system. In this work, we develop numerical simulations of global tectonism with impacting effects, and simulate the evolution of these models throughout the Archaean for given impact fluxes. We demonstrate that moderate-size (∼70 km diameter) impactors are capable of initiating short-lived subduction, and that the system response is sensitive to impactor size, proximity to other impacts, and also lithospheric thickness gradients. Large lithospheric thickness gradients may have first appeared at ca. 3.5–3.2 Ga as cratonic roots, and we postulate an association between Earth’s thermal maturation, cratonic root stability, and the onset of widespread sporadic tectonism driven by the impact flux at this time. 

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2. Archaean seafloors shallowed with age due to radiogenic heating in the mantle

   https://doi.org/10.1038/s41561-020-00673-1  

   Rosas, Juan Carlos; Korenaga, Jun (January 2021, Nature Geoscience)

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3. A multiple sulfur record of super-large volcanic eruptions in Archaean pyrite nodules

   https://doi.org/10.1016/j.epsl.2022.117737  

   Agangi, Andrea; Hofmann, Axel; Eickmann, Benjamin; Ossa Ossa, Frantz; Tyler, Perinne; Wing, Boswell; Bekker, Andrey (September 2022, Earth and Planetary Science Letters)
4. Water and Rock Chemistry Inform Our Understanding of the Deep Biosphere: Case Study in an Archaean Banded Iron Formation

   https://doi.org/10.3389/feart.2022.803250  

   Schuler, Cristopher J.; Briscoe, Lindsey J.; Alexander, Scott C.; Alexander, E. Calvin; Gralnick, Jeffrey A.; Santelli, Cara M.; Toner, Brandy M. (March 2022, Frontiers in Earth Science)

   Research into the deep biosphere requires an understanding of both the microbial community at a given site and the geochemical and hydrological factors that support that microbial community. To highlight the interplay between geochemistry and microbiology in these deep environments, we characterized the hydrogeologic and geochemical systems of a 2.7 Ga banded iron formation within the Canadian Shield in the Soudan Underground Mine State Park in Minnesota, United States, a site known to host a lithotrophic microbial community. Calcium-sodium-chloride brines, characteristic of deep groundwaters throughout the Canadian Shield, were found in the site with total dissolved constituents (<0.2 micron) as high as 116,000 mg/L (ppm) in one borehole. Comparison of the Soudan waters to those found at other sites in the Canadian Shield or other sites of deep biosphere research indicate that they are notable for their high magnesium concentrations relative to total salinity. Additionally, the most saline Soudan waters have distinct 2 H and 18 O water isotope values suggesting long periods of isolation from the surface, which would allow for the evolution of a distinctive subsurface community. The presence of the banded iron formation along with the long-term isolation of the shield waters make Soudan a site of great potential for future research into deep crustal life. Furthermore, our work at Soudan highlights how geochemical data can inform future research into the deep biosphere and highlights a path for future research at the mine. 

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