Genesis: early life survived in the Polar Circles by precipitating banded iron formation (~ 3.7–1.85 Ga) followed by stratified ferruginous siliciclasts until ~ 580 Ma, when tectonically shifted to lower latitudes initiating the ‘Cambrian Explosion’

• Published in: International journal of earth sciences : Geologische Rundschau 2022, Vol.111 (5), p.1593-1607
• Main Author: Lewy, Zeev
• Format: Article
• Language: English
• Subjects: Anoxia; Axes of rotation; Bacteria; Biota; Cambrian; Chemical interactions; Chemical precipitation; Chemoautotrophic bacteria; Climate change; Climatic extremes; Convection; Convection currents; Darkness; Dilution; Earth and Environmental Science; Earth axis; Earth rotation; Earth Sciences; Environmental changes; Eukaryotes; Evaporation; Evaporation and condensation; Evolution; Extreme values; Fluids; Freezing; Geochemistry; Geology; Geophysics/Geodesy; Heat budget; Hydrothermal solutions; Iron; Iron ores; Iron oxides; Lakes; Meteoric water; Mineral Resources; Ores; Oxidation; Oxygen; Photosynthesis; Planetary rotation; Plate tectonics; Polar environments; Polar regions; Precambrian; Review Article; Sedimentology; Silica; Solar radiation; Structural Geology; Survival; Tectonics; Ultraviolet radiation
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-022-02194-1

The inclination of Planet Earth’s axis of rotation by 23½° resulted in extreme climatic changes. Weak, solar radiation upon the Polar Circles during half-a-year alternated with half-a-year of darkness, turning them into freezing terrains for nearly the whole Precambrian. Exhalant hydrothermal solutions formed huge lakes over Polar Regions, undergoing intensive evaporation and condensation. Chemical interactions incidentally created primitive live forms, surviving as chemoautotrophic bacteria under the weakest UV rays. Daily changing solar radiation emitting UV rays over low latitudes prevented any life form. Some of these polar bacteria developed photosynthesis, improving their nourishment simultaneously releasing oxygen. The high content of ferrous iron in the lakes absorbed toxic oxygen forming iron oxides as banded iron formation (BIF). Excess photosynthetic oxygen molecules escaped into the anoxic atmosphere. At ~ 1.8 Ga oxygenated meteoric water infiltrated the continental subsurface oxidizing hydrothermal fluids, precipitating underground layered iron-oxides followed by silica only during the dry summers. The dilution of the rising solutions terminated biologically induced BIF precipitation. Consequently, intensive evaporation cemented sililiciclasts into stratified ferruginous formations, becoming abundant in the Late Neoproterozoic as NIF. The co-occurrence of Paleoproterozoic BIF and Neoproterozoic NIF sites evidence the tectonic and climatic stability of the Polar Circles. Magmatic convection currents split them ~ 750 Ma ago, but only after 580 Ma shifted the individual plates radially to low latitudes with advance of ‘Plate Tectonics’. The polar bacteria connected with the open sterile sea for the first time had to adapt to daily changing ecosystems by combining into mobile primitive eukaryotes (Ediacaran Biota) and further diversify, erroneously referred to the ‘Cambrian Explosion’. Geological evidence corroborated the activity of convection currents since Earth’s consolidation controlling its inner heat budget and supplying hydrothermal solutions forming lakes on the Polar Circles where life originated and iron ores accumulated.