Browsing by Author "Porter, Susannah M."

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    Atmosphere-ocean oxygen and productivity dynamics during the Cambrian explosion
    Dahl, Tais W.; Connelly, James N.; Li, Da; Kouchinsky, Artem; Gill, Benjamin C.; Porter, Susannah M.; Maloof, Adam C.; Bizzarro, Martin (2019-08-21)
    Large, motile animals proliferated during the Cambrian explosion,540–515 million years ago,and this period has been associated with both rising and declining O2levels on Earth [1–3]. To explore this conundrum, we reconstructed the global extent of seafloor oxygenation at ~sub-million year resolution based on U isotope compositions in 187 marine limestone samples from China, Siberia and Morocco,and coupled this record to simulations of atmospheric O2 levels using a mass balance model constrained by carbon, sulfur and strontium isotopes in the same rocks.The studied samples were investigated petrographically and geochemically to disentangle isotope fractionation processes occurring locally during diagenesis from secular changes in open seawater. We find that Sr/Ca, Mg/Ca and G18O help discriminate carbonate samples with a larger G238U offset from contemporaneous seawater, and decipher the signal that can be ascribed to global changes in the oceanic U pool. Our data demonstrate two significant expansions of seafloor anoxia in the aftermath of an interval with declining atmospheric pO2levels.The combination of atmospheric and oceanic O2records offers a self-consistent and highly dynamic picture of atmosphere-ocean oxygenation in which the evolving animal ecosystems might have both responded and contributed to global environmental change.Animals diversified possibly by a predator-prey arms race peaking in two pulses interrupted by these dramatic fluctuations in seafloor anoxia. When O2levels again rose, it occurred in concert with predicted high rates of photosynthetic production, both of which may have fueled more energy to predators and their armored prey in the evolving marine ecosystem.
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    Atmosphere–ocean oxygen and productivity dynamics during early animal radiations
    Dahl, Tais W.; Connelly, James N.; Li, Da; Kouchinsky, Artem; Gill, Benjamin C.; Porter, Susannah M.; Maloof, Adam C.; Bizzarro, Martin (National Academy of Sciences, 2019-09-24)
    The proliferation of large, motile animals 540 to 520 Ma has been linked to both rising and declining O₂ levels on Earth. To explore this conundrum, we reconstruct the global extent of seafloor oxygenation at approximately submillion-year resolution based on uranium isotope compositions of 187 marine carbonates samples from China, Siberia, and Morocco, and simulate O₂ levels in the atmosphere and surface oceans using a mass balance model constrained by carbon, sulfur, and strontium isotopes in the same sedimentary successions. Our results point to a dynamically viable and highly variable state of atmosphere–ocean oxygenation with 2 massive expansions of seafloor anoxia in the aftermath of a prolonged interval of declining atmospheric pO₂ levels. Although animals began diversifying beforehand, there were relatively few new appearances during these dramatic fluctuations in seafloor oxygenation. When O₂ levels again rose, it occurred in concert with predicted high rates of photosynthetic production, both of which may have fueled more energy to predators and their armored prey in the evolving marine ecosystem.
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    Biomineralization by particle attachment in early animals
    Gilbert, Pupa U. P. A.; Porter, Susannah M.; Sun, Chang-Yu; Xiao, Shuhai; Gibson, Brandt M.; Shenkar, Noa; Knoll, Andrew H. (National Academy of Sciences, 2019-08-19)
    Crystallization by particle attachment (CPA) of amorphous precursors has been demonstrated in modern biomineralized skeletons across a broad phylogenetic range of animals. Precisely the same precursors, hydrated (ACC-H₂O) and anhydrous calcium carbonate (ACC), have been observed spectromicroscopically in echinoderms, mollusks, and cnidarians, phyla drawn from the 3 major clades of eumetazoans. Scanning electron microscopy (SEM) here also shows evidence of CPA in tunicate chordates. This is surprising, as species in these clades have no common ancestor that formed a mineralized skeleton and appear to have evolved carbonate biomineralization independently millions of years after their late Neoproterozoic divergence. Here we correlate the occurrence of CPA from ACC precursor particles with nanoparticulate fabric and then use the latter to investigate the antiquity of the former. SEM images of early biominerals from Ediacaran and Cambrian shelly fossils show that these early calcifiers used attachment of ACC particles to form their biominerals. The convergent evolution of biomineral CPA may have been dictated by the same thermodynamics and kinetics as we observe today.
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    The Sedimentary Geochemistry and Paleoenvironments Project
    Farrell, Una C.; Samawi, Rifaat; Anjanappa, Savitha; Klykov, Roman; Adeboye, Oyeleye O.; Agic, Heda; Ahm, Anne-Sofie C.; Boag, Thomas H.; Bowyer, Fred; Brocks, Jochen J.; Brunoir, Tessa N.; Canfield, Donald E.; Chen, Xiaoyan; Cheng, Meng; Clarkson, Matthew O.; Cole, Devon B.; Cordie, David R.; Crockford, Peter W.; Cui, Huan; Dahl, Tais W.; Mouro, Lucas D.; Dewing, Keith; Dornbos, Stephen Q.; Drabon, Nadja; Dumoulin, Julie A.; Emmings, Joseph F.; Endriga, Cecilia R.; Fraser, Tiffani A.; Gaines, Robert R.; Gaschnig, Richard M.; Gibson, Timothy M.; Gilleaudeau, Geoffrey J.; Gill, Benjamin C.; Goldberg, Karin; Guilbaud, Romain; Halverson, Galen P.; Hammarlund, Emma U.; Hantsoo, Kalev G.; Henderson, Miles A.; Hodgskiss, Malcolm SW W.; Horner, Tristan J.; Husson, Jon M.; Johnson, Benjamin; Kabanov, Pavel; Brenhin Keller, C.; Kimmig, Julien; Kipp, Michael A.; Knoll, Andrew H.; Kreitsmann, Timmu; Kunzmann, Marcus; Kurzweil, Florian; LeRoy, Matthew A.; Li, Chao; Lipp, Alex G.; Loydell, David K.; Lu, Xinze; Macdonald, Francis A.; Magnall, Joseph M.; Mand, Kaarel; Mehra, Akshay; Melchin, Michael J.; Miller, Austin J.; Mills, N. Tanner; Mwinde, Chiza N.; O'Connell, Brennan; Och, Lawrence M.; Ossa Ossa, Frantz; Pages, Anais; Paiste, Kart; Partin, Camille A.; Peters, Shanan E.; Petrov, Peter; Playter, Tiffany L.; Plaza-Torres, Stephanie; Porter, Susannah M.; Poulton, Simon W.; Pruss, Sara B.; Richoz, Sylvain; Ritzer, Samantha R.; Rooney, Alan D.; Sahoo, Swapan K.; Schoepfer, Shane D.; Sclafani, Judith A.; Shen, Yanan; Shorttle, Oliver; Slotznick, Sarah P.; Smith, Emily F.; Spinks, Sam; Stockey, Richard G.; Strauss, Justin V.; Stueken, Eva E.; Tecklenburg, Sabrina; Thomson, Danielle; Tosca, Nicholas J.; Uhlein, Gabriel J.; Vizcaino, Maoli N.; Wang, Huajian; White, Tristan; Wilby, Philip R.; Woltz, Christina R.; Wood, Rachel A.; Xiang, Lei; Yurchenko, Inessa A.; Zhang, Tianran; Planavsky, Noah J.; Lau, Kimberly V.; Johnston, David T.; Sperling, Erik A. (Wiley, 2021-07-05)
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    A template for an improved rock-based subdivision of the pre-Cryogenian timescale
    Shields, Graham A.; Strachan, Robin A.; Porter, Susannah M.; Halverson, Galen P.; Macdonald, Francis A.; Plumb, Kenneth A.; de Alvarenga, Carlos J.; Banerjee, Dhiraj M.; Bekker, Andrey; Bleeker, Wouter; Brasier, Alexander; Chakraborty, Partha P.; Collins, Alan S.; Condie, Kent; Das, Kaushik; Evans, David AD D.; Ernst, Richard; Fallick, Anthony E.; Frimmel, Hartwig; Fuck, Reinhardt; Hoffman, Paul F.; Kamber, Balz S.; Kuznetsov, Anton B.; Mitchell, Ross N.; Poire, Daniel G.; Poulton, Simon W.; Riding, Robert; Sharma, Mukund; Storey, Craig; Stueeken, Eva; Tostevin, Rosalie; Turner, Elizabeth; Xiao, Shuhai; Zhang, Shuanhong; Zhou, Ying; Zhu, Maoyan (Geological Society of America, 2021-07-07)
    The geological timescale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current timescale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era-and period-level subdivisions. Our review leads to the following conclusions: (1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and (2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods ( pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.