Low oxygen and argon in the Neoproterozoic atmosphere at 815 Ma

Simple item page
dc.citation.firstpage66en_US
dc.citation.journalTitleEarth and Planetary Science Lettersen_US
dc.citation.lastpage74en_US
dc.citation.volumeNumber480en_US
dc.contributor.authorYeung, Laurence Y.en_US
dc.date.accessioned2018-06-27T14:39:40Zen_US
dc.date.available2018-06-27T14:39:40Zen_US
dc.date.issued2017en_US
dc.description.abstractThe evolution of Earth's atmosphere on >106-yr timescales is tied to that of the deep Earth. Volcanic degassing, weathering, and burial of volatile elements regulates their abundance at the surface, setting a boundary condition for the biogeochemical cycles that modulate Earth's atmosphere and climate. The atmosphere expresses this interaction through its composition; however, direct measurements of the ancient atmosphere's composition more than a million years ago are notoriously difficult to obtain. Gases trapped in ancient minerals represent a potential archive of the ancient atmosphere, but their fidelity has not been thoroughly evaluated. Both trapping and preservation artifacts may be relevant. Here, I use a multi-element approach to reanalyze recently collected fluid-inclusion data from halites purportedly containing snapshots of the ancient atmosphere as old as 815 Ma. I argue that those samples were affected by the concomitant trapping of air dissolved in brines and contaminations associated with modern air. These artifacts lead to an apparent excess in O2 and Ar. The samples may also contain signals of mass-dependent fractionation and biogeochemical cycling within the fluid inclusions. After consideration of these artifacts, this new analysis suggests that the Tonian atmosphere was likely low in O2, containing ≤10% present atmospheric levels (PAL), not ∼50% PAL as the data would suggest at face value. Low concentrations of O2 are consistent with other geochemical constraints for this time period and further imply that the majority of Neoproterozoic atmospheric oxygenation occurred after 815 Ma. In addition, the analysis reveals a surprisingly low Tonian Ar inventory—≤60% PAL—which, if accurate, challenges our understanding of the solid Earth's degassing history. When placed in context with other empirical estimates of paleo-atmospheric Ar, the data imply a period of relatively slow atmospheric Ar accumulation in the Paleo- and Meso-Proterozoic, followed by extensive degassing in the late Neoproterozoic or early Cambrian, before returning to a relatively quiescent state by the Devonian. This two-step structure resembles that for the evolution of atmospheric O2, hinting at a common driving force from the deep Earth. Some caution is warranted, however, because still more enigmatic contaminations than the ones presented here may be relevant. Gases trapped in minerals may offer important constraints on the evolution of Earth's surface, climate, and atmosphere, but potential contaminations and other confounding factors need to be considered carefully before these records can be considered quantitative.en_US
dc.identifier.citationYeung, Laurence Y.. "Low oxygen and argon in the Neoproterozoic atmosphere at 815 Ma." <i>Earth and Planetary Science Letters,</i> 480, (2017) Elsevier: 66-74. https://doi.org/10.1016/j.epsl.2017.09.044.en_US
dc.identifier.doihttps://doi.org/10.1016/j.epsl.2017.09.044en_US
dc.identifier.urihttps://hdl.handle.net/1911/102301en_US
dc.language.isoengen_US
dc.publisherElsevieren_US
dc.rightsThis is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier.en_US
dc.subject.keywordatmospheric oxygenationen_US
dc.subject.keywordfluid inclusionsen_US
dc.subject.keywordgas analysisen_US
dc.subject.keywordsolid earth degassingen_US
dc.titleLow oxygen and argon in the Neoproterozoic atmosphere at 815 Maen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpost-printen_US
Files
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
ArgonEvolution-v2.pdf
Size:
374.96 KB
Format:
Adobe Portable Document Format
Description:
Download
Collections
Faculty Publications
Earth, Environmental and Planetary Sciences Publications