This project is triggered by the recent discovery of extreme oxygen (-26 per mil) and hydrogen (-233 per mil) isotope depletion for Paleoproterozoic metamorphic rocks in the Belomorian Belt in Karelia, Russia that represent the world's lowest values found so far. This project requests funding to extend a preliminary study that demonstrates that these depleted ratios are present in a large geographical area (over 200 km long and several tens of kilometers wide). The current hypothesis to be tested is that these rocks inherited their low isotopic values through high-temperature water-rock interaction in rift zone that existed 2.4 billion years ago. Oxygen and hydrogen stable isotope compositions of less than 0 per mil (relative to the isotopic standard SMOW) exist only in meteoric water that went through the Rayleigh evaporation-precipitation cycle, and such negative isotopic values are characteristic of ice from polar regions. Current paleogeographic and paleomagnetic models suggest that Karelia was located near the equator throughout the Paleoproterozoic, and such low isotopic ratios are consistent with an interpretation that they formed during the first known panglacial episode in the Paleoproterozoic. In order to achieve such isotopic depletion through vapor distillation a liquid reservoir of water/oceans must remain unfrozen. This so-called 'Slushball Earth' model contrasts with the more commonly accepted Snowball Earth model where no unfrozen water remains on the surface of the planet. The climate stability and the albedo effects of a Slushball Earth have been discussed and questioned. Current climate models suggest that if 2/3 of the high latitude surface is frozen, the runaway effect will lead to a hard Snowball Earth outcome. If this depleted stable isotope composition of the Karelian rocks can be shown to be extensive, it may signify that the hydrologic meteoric water cycle must be in operation during the panglacial episodes, thus serving as the first material evidence of the stability of the Slushball Earth climate model.
The scope of this project will include further characterization and isotopic mapping of the anomalously depleted area, determination of the time of oxygen isotope depletion via combination of in situ isotopic and geochronologic methods, as well as field and trace element investigation of samples to identify their protolith, and geochronologic and geochemical correlation with the lower metamorphic grade, early Paleoproterozoic Sariolian, and Sumian sedimentary sequences in the Fennoscandia. The proposal will explore extreme climate condition happening just before or during the rise of atmospheric oxygen and diversification of primitive life forms. This project will promote international collaboration, involve and support students traditionally underrepresented in geosciences, involve undergraduate and community college students in research and expose them to science and international collaboration, and support the analytical infrastructure of the stable isotope lab at the University of Oregon.
" PI: Ilya Bindeman, University of Oregon Geologic records of Earth’s hydrosphere and meteoric precipitation older than 2 billon years (Ga) are very rare, although they provide insight into the past climate, rates of water-rock interaction, and intensity of plate tectonics. The period of Earth’s history from 2.5 to 2.1 Ga is likely the most important in understanding the evolution of our planet. By 2.3 Ga, the Earth had enough free oxygen in the air, after so-called the Great Oxidation Event. This was preceded by a series of at least three glaciations, of still unconstrained age and extent. By studying volcanic and now metamorphic rocks from Karelia, Fennoscadian Shield, we discovered first isotopic evidence of glaciers that were present at low to mid latitudes from 2.5 to 2.2 Ga. The extremely oxygen 18-O depleted (-27.3‰) and deuterium depleted (-233‰) isotopic record (the world’s lowest measured in rocks) unequivocally suggests that the oxygen in these rocks was derived from glacial meltwaters, and that process of water rock interaction proceeded in subglacial rift zones, creating these depletions. Paleogeographic reconstructions indicate that Karelia was at low to middle latitudes throughout the Paleoproterozoic Era. We have now characterized 11 localities of over 450 km long belt suggesting that glaciations were extensive in space, and dating of zircons preliminary suggested that we have found evidence of at least two pan-global glaciations at 2.4 and 2.23 billion years ago. Additionally, ultradepleted 18-O-waters outside of polar regions or the interiors of large landmasses provide independent evidence for a moderately glaciated, so called "slushball" Earth climate between 2.45 and 2.2 billion years ago, in which low- or mid-latitude, midsize continents were covered with glaciers while the ocean remained at least partially unfrozen to allow for intracontinental isotopic distillation in a large temperature gradient. The climate stability and albedo effects of the "hard snowball" vs "slushball" have been discussed and questioned and an intermediate Jormangund climate model has been proposed. Our collaborators are testing isotopic distillation models using global circulation models. The proposal may prove to be critical in deciding which of the three Paleoproterozoic glaciations caused the Global Oxidation Event, and precisely determine its timing. The proposal promoted international collaboration and supported students traditionally underrepresented in geosciences, involved undergraduate and community college students in research and expose them to science and international collaboration. The proposal supported analytical infrastructure of the recently established stable isotope lab at the University of Oregon, through work done by the PI and members of the research group and collaborators.
