Global volatile cycles on early Earth

• Applicant: Professorin Dr. Lena Noack
• Subject Area: Geophysics
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 404674808

While Earth is a planet where for present-day processes in the interior and at the surface we have a wealth of information, data for the early evolution of the planet is sparse. Apart from few zircon inclusions that date back to Hadean times, first rock samples are limited to the end of the Eoarchaean and to the Archean time. These rock samples, while providing interesting single observations of early Earth’s surface, are only some pieces of a much larger puzzle that we still need to solve to be able to explain why Earth developed to the unique habitable planet that we know. One of the questions that still remain to be answered is by which mechanisms volatiles could be recycled into the upper mantle before the on-set of plate tectonics as it operates today. Subsequent melting of recycled, hydrated crust is needed to explain the chemical composition of Earth’s earliest crust. On the other hand, it is not clear how representative the surviving Archean crust is. Geological measurements can therefore only be interpreted correctly in a global context, if they are combined with a general understanding of early Earth processes. This can be obtained by making use of computational models that can then complement the geological record to constrain evolution scenarios of early Earth. In the proposed project, we will enhance a thermo-chemical model of Earth’s mantle, lithosphere and crust by including volatile cycles (focussing mainly on H, C and N that form greenhouse gases, but also Xe, Ar and Ne as trace elements) from interior to surface and vice versa. The cycles operate via outgassing, condensation and crustal recycling. We will then compare our model predictions with respect to volatiles to the collected early Earth data. Such a model approach allows to investigate the evolution of volatile reservoirs and isotope relations over time. Using a Monte-Carlo method, we will then model different evolution scenarios for early Earth for random initial thermal and compositional (in terms of volatiles) states of Earth’s interior after the Moon-forming impact. The resulting evolution scenarios can then be matched with field data (especially concerning isotope ratios of noble gases). Constraints set by the Archaean geological record can also help to indicate how the earliest evolution of Earth needed to evolve to explain the later available geological and geochemical samples.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1833: Building a Habitable Earth