In-situ dating of the Earth's oldest trace fossil at 3.34 Ga

Paleoarchean trace fossils in altered volcanic glass

“…The 85-m-thick dolerite-diorite dike and the pillow lavas 18-19 m away from the dike yielded a nicely clustering U/Pb titanite age distribution at ca. 2.9 Ga, about 450 Ma later than earlier studies of biotexturereplacing titanites from a sample that was taken 55-60 m away from this dike (24). Grosch and McLoughlin (6) interpreted these data such that these titanites were formed as a retrograde mineral subsequent to contact metamorphism from the dike intrusion and rejected earlier interpretations that the more distant samples reflect biotexture replacements shortly after formation of these pillow lavas.…”

“…Then they were uplifted and eroded to within 70 m below a regional unconformity and then overlain by shallow water to subaerial terrestrial sediments dated at ca. 3.458 Ga. U/Pb titanite ages for biotexture replacements in samples in the BGB yielded an age of 3.342 ± 0.068 Ba (24), postdating the Hooggenoeg eruption age by a time period that is consistent with the duration of bioalteration of in situ oceanic crust. During this time, the BGB is likely to have been submerged based on global heat loss arguments (28) and the geology of overlying sediment (29).…”

“…Recent U/Pb isotopic ages of titanite microstructures in the BGB pillow lavas (6) yielded much younger ages than an earlier study (24), and this discrepancy was used to reject biogenicity of putative biotextures in BGB pillow lavas (6). To explore these issues, we have to understand the duration of glass bioalteration in Cenozoic ocean crust, the age differences between BGB pillow lavas and their titanite biotextures, and how titanite ages may or may not be used to understand their biogenicity.…”

“…Much of the current discussion revolves around the geological history of the BGB and how to interpret the recently emerging discrepancies in titanite U/Pb geochronological data (6,24). The early geological history of Hooggenoeg pillow lavas is well known (12,27): They erupted at >2 km ocean depth between 3.47 and 3.46 Ga and underwent in situ hydrothermal metamorphism.…”

Ultra-Deep Drilling through 3.5-Billion-Year-Old Crust in South Africa

“…In view of these uncertainties and controversies, it is clear that elucidating how and when life may have originated on Earth requires first to understand the conditions that prevailed early in Earth's history and the environments in which life may have appeared and later evolved. The recent discovery (Furnes et al, 2004) and in situ dating of ichnofossils in the rims of the world's oldest pillow lavas in Barberton (Fliegel et al, 2010) has dramatically shown that rocks previously ignored in studies of early life (e.g., basaltic igneous rocks) now offer a new paleoenvironment as habitats for early life. This holds great potential to track life back even further in time and must be considered a promising focus for such early life studies in places like the Barberton Greenstone Belt.…”