More Like this

1. A new model of the Earth system nitrogen cycle: how plates and life affect the atmosphere

   Johnson, Benjamin W.; Goldblatt, Colin (January 2017, AGU Fall Meeting)

   Nitrogen is the main component of Earth’s atmosphere. It plays a key role in the evolution of the biosphere and surface of Earth [1]. There are contrasting views, however, on how N has evolved on the surface of the Earth over time. Some modeling efforts [e.g., 2] indicate a steady-state level of N in the atmosphere over geologic time, while geochemical [e.g., 3], other proxies [e.g., 4], and more recent models [5] indicate the mass of N in the atmosphere can change dramatically over Earth history. This conundrum, and potential solutions to it, present distinct interpretations of the history of Earth, and teleconnections between the surface and interior of the planet have applications to other terrestrial bodies as well. To help investigate this conundrum, we have constructed an Earth-system N cycle box model. To our knowledge, this is the most capable model for addressing evolution of the N reservoirs of Earth through time. The model combines biologic and geologic processes, driven by a mantle cooling history, to more fully describe the N cycle through geologic history. In addition to a full biologic N cycle (fixing, nitrification, denitrification), we also dynamically solve for PO4 through time and we have a prescribed O2 history. Results indicate that the atmosphere of Earth could have experienced major changes in mass over geologic time. Importantly, the amount of N in the atmosphere today appears to be directly related to the total N budget of the silicate Earth. For example, high initial atmospheric mass, suggested as a solution to the Faint Young Sun Paradox [1], is drawn down over time. This supports work that indicates the mantle has significantly more N than the atmosphere does today [6]. Contrastingly, model runs with low total N result in a crash in atmospheric mass. In nearly all model runs the bulk silicate Earth contains the majority of the planet's N. [1] Goldblatt et al. (2009) Nat. Geosci., 2, 891-896. [2] Berner, R. (2006) Geology., 34, 413-415. [3] Barry, P.H. and Hilton (2016) Geochem. Persp. Letters, 2, 148-159. [4] Som, S.M. et al. (2016) Nat. Geosci., 9, 448-451. [5] Stueken et al. (2016) Astrobiology, 16, in press. [6] Johnson et al. (2015) Earth Science Reviews, 148,150-173. 

   more » « less
2. A new model of the Earth system nitrogen cycle: how plates and life affect the atmosphere

   Johnson, Benjamin W; Goldblatt, Colin (October 2017, Habitable Worlds 2017)

   Nitrogen is the main component of Earth’s atmosphere. Nitrogen plays a key role in the evolution of the biosphere and surface of Earth [1]. There are contrasting views, however, on how N has evolved on the surface of the Earth over time. Some modeling efforts [e.g., 2] indicate a steady-state level of N in the atmosphere over geologic time, while geochemical [e.g., 3], other proxies [e.g., 4], and more recent models [5] indicate the mass of N in the atmosphere can change dramatically over Earth history. This conundrum, and potential solutions to it, present distinct interpretations of the history of Earth, and teleconnections between the surface and interior of the planet have applications to other terrestrial bodies as well. To help investigate this conundrum, we have constructed an Earth-system N cycle box model. To our knowledge, this is the most capable model for addressing evolution of the N reservoirs of Earth through time. The model combines biologic and geologic processes, driven by a mantle cooling history, to more fully describe the N cycle through geologic history. In addition to a full biologic N cycle (fixing, nitrification, denitrification), we also dynamically solve for PO4 through time and we have a prescribed O2 history. Initial model results indicate that the atmosphere of Earth could have experienced major changes in mass over geologic time. High initial atmospheric mass, suggested as a solution to the Faint Young Sun Paradox [1], is drawn down over time, supports work that indicates the mantle has significantly more N than the atmosphere does today [6]. Importantly, the amount of N in the atmosphere today is directly dependent on the total N mass in the silicate Earth. Thus, given some assumptions, the atmosphere itself may be a proxy for total planetary N. References: Use the brief numbered style common in many abstracts, e.g., [1], [2], etc. References should then appear in numerical order in the reference list, and should use the following abbreviated style: [1] Goldblatt et al. (2009) Nat. Geosci., 2, 891-896. [2] Berner, R. (2006) Geology., 34, 413-415. [3] Barry, P.H. and Hilton (2016) Geochem. Persp. Letters, 2, 148-159. [4] Som, S.M. et al. (2016) Nat. Geosci., 9, 448-451. [5] Stueken et al. (2016) Astrobiology, 16, in press. [6] Johnson et al. (2015) Earth Science Reviews, 148,150-173. 

   more » « less
3. Sedimentary record of oceanic plateau accretion: Revisiting the Eocene to Miocene stratigraphy of the northern Olympic Peninsula, Washington (USA)

   https://doi.org/10.1130/GES02778.1  

   Donaghy, Erin E; Eddy, Michael P; Ridgway, Kenneth D; Ickert, Ryan B (November 2024, Geosphere)

   Abstract Oceanic plateaus are common in modern oceanic basins and will ultimately collide with continental subduction zones. Despite the frequency of these events, complete sedimentary records of oceanic plateau collision and accretion have remained limited to only a few Cenozoic examples with excellent exposure and tectonic context. Our study focuses on building a stratigraphic record of plateau collision using the sedimentary strata deposited on the Siletzia oceanic plateau, which accreted to the Pacific Northwest at ca. 50 Ma. By combining previously published provenance and stratigraphic data with new lithofacies and geologic mapping, measured stratigraphic sections, conglomerate clast counts, and U-Pb zircon geochronology, we were able to divide the strata of the northern Olympic Peninsula in Washington, USA, into precollisional, syn-collisional, and postcollisional stages. Precollisional strata include early Eocene deep-marine hemipelagic to pelagic mudstones of the Aldwell Formation that were deposited directly on Siletzia basalts. These strata were deformed during collision and are separated from the overlying syn-collisional middle Eocene sandstone and conglomerate of the marine (?) Lyre Formation by an angular unconformity. Postcollisional strata were deposited by submarine fans and include interbedded sandstone and siltstone of the Hoko River and Makah formations. These units initially record the filling of isolated trench-slope basins by late Eocene time before eventual integration into an Oligocene regional forearc basin as the accreted Siletzia plateau began to subside. Our chronostratigraphy permits the correlation of basin strata across tectonic domains and provides more general insight into how forearc sedimentary systems evolve following the accretion of a young, buoyant oceanic plateau. 

   more » « less
4. Deep Dust: An ICDP Drilling Project to Probe Continental Climate from the Late-Paleozoic Icehouse to the end-Permian Hothouse

   https://doi.org/10.5194/egusphere-egu25-8251  

   Feulner, Georg; Soreghan, Gerilyn S; Bedle, Heather; Benison, Kathleen; Bourquin, Sylvie; Hamamura, Natsuko; Hinnov, Linda; Moscariello, Andrea; Noren, Anders; Pfeifer, Lily; et al (March 2025, European Geophysical Union)

   The Permian witnessed some of the most profound climatic, biotic, and tectonic events in Earth’s history. Global orogeny leading to the assembly of Pangea culminated by middle Permian time, and included multiple orogenic belts in the equatorial Central Pangean Mountains, from the Variscan-Hercynian system in the East to the Ancestral Rocky Mountains in the West. Earth’s penultimate global icehouse peaked in early Permian time, transitioning to full greenhouse conditions by late Permian time, constituting the only example of icehouse collapse on a fully vegetated Earth. The Late Paleozoic Ice Age was the longest and most intense glaciation of the Phanerozoic. Reconstructions of atmospheric composition in the Permian record the lowest CO2 and highest O2 levels of the Phanerozoic, with average CO2 levels comparable to the Quaternary, rapidly warming climate. Fundamental shifts occurred in atmospheric circulation: a global megamonsoon developed, and the tropics became anomalously arid with time. Extreme environments are well documented in the form of voluminous dust deposits, acid-saline lakes and groundwaters, extreme continental temperatures and aridity, and major shifts in biodiversity, ultimately culminating in the largest extinction of Earth history at the Permian-Triassic boundary.The Deep Dust project seeks to elucidate paleoclimatic conditions and forcings through the Permian at temporal scales ranging from millennia to Milankovitch cycles and beyond by acquiring continuous core in continental lowlands known to harbor stratigraphically complete records dominated by loess and lacustrine strata. Our initial site is in the midcontinental U.S.— the Anadarko Basin (Oklahoma), which harbors a complete continental Permian section from western equatorial Pangaea. We will also address the nature and character of the modern and fossil microbial biosphere, the chemistry of saline lake waters and groundwaters, Mars-analog conditions, and exhumation histories of source regions. Importantly, data from Deep Dust will be integrated with Earth-system modelling. This is crucial for putting the (necessarily local) drill core data into the broader global context and for understanding relevant mechanisms and feedbacks of the Permian Earth system. 

   more » « less
5. 86Kr excess and other noble gases identify a billion-year-old radiogenically-enriched groundwater system

   https://doi.org/10.1038/s41467-022-31412-2  

   Warr, O.; Ballentine, C. J.; Onstott, T. C.; Nisson, D. M.; Kieft, T. L.; Hillegonds, D. J.; Sherwood Lollar, B. (June 2022, Nature Communications)

   Abstract Deep within the Precambrian basement rocks of the Earth, groundwaters can sustain subsurface microbial communities, and are targets of investigation both for geologic storage of carbon and/or nuclear waste, and for new reservoirs of rapidly depleting resources of helium. Noble gas-derived residence times have revealed deep hydrological settings where groundwaters are preserved on millions to billion-year timescales. Here we report groundwaters enriched in the highest concentrations of radiogenic products yet discovered in fluids, with an associated⁸⁶Kr excess in the free fluid, and residence times >1 billion years. This brine, from a South African gold mine 3 km below surface, demonstrates that ancient groundwaters preserved in the deep continental crust on billion-year geologic timescales may be more widespread than previously understood. The findings have implications beyond Earth, where on rocky planets such as Mars, subsurface water may persist on long timescales despite surface conditions that no longer provide a habitable zone. 

   more » « less